MacLochlainns Weblog

Michael McLaughlin's Technical Blog

Site Admin

Archive for the ‘MySQL Development’ tag

Learning SQL Exercise

without comments

I’ve been using Alan Beaulieu’s Learning SQL to teach my SQL Development class with MySQL 8. It’s a great book overall but Chapter 12 lacks a complete exercise. Here’s all that the author provides to the reader. This is inadequate for most readers to work with to solve the concept of a transaction.

Exercise 12-1

Generate a unit of work to transfer $50 from account 123 to account 789. You will need to insert two rows into the transaction table and update two rows in the account table. Use the following table definitions/data:

                      Account:
account_id     avail_balance    last_activity_date
-----------    --------------   ------------------
       123               450    2019-07-10 20:53:27
       789               125    2019-06-22 15:18:35
 
                      Transaction:
txn_id    txn_date      account_id    txn_type_cd    amount
------    ----------    -------+--    -----------    ------
  1001    2019-05-15           123    C                 500
  1002    2019-06-01           789    C                  75

Use txn_type_cd = ‘C” to indicate a credit (addition), and use txn_type_cd = ‘D’ to indicate a debit (substraction).

New Exercise 12-1

The problem with the exercise description is that the sakila database, which is used for most of the book, doesn’t have transaction or account tables. Nor, are there any instructions about general accounting practices or principles. These missing components make it hard for students to understand how to build the transaction.

The first thing the exercise’s problem defintion should qualify is how to create the account and transaction tables, like:

  1. Create the account table, like this with an initial auto incrementing value of 1001:

    -- +--------------------+--------------+------+-----+---------+----------------+
    -- | Field              | Type         | Null | Key | Default | Extra          |
    -- +--------------------+--------------+------+-----+---------+----------------+
    -- | account_id         | int unsigned | NO   | PRI | NULL    | auto_increment |
    -- | avail_balance      | double       | NO   |     | NULL    |                |
    -- | last_activity_date | datetime     | NO   |     | NULL    |                |
    -- +--------------------+--------------+------+-----+---------+----------------+
  2. Create the transaction table, like this with an initial auto incrementing value of 1001:

    -- +----------------+--------------+------+-----+---------+----------------+
    -- | Field          | Type         | Null | Key | Default | Extra          |
    -- +----------------+--------------+------+-----+---------+----------------+
    -- | txn_id         | int unsigned | NO   | PRI | NULL    | auto_increment |
    -- | txn_date       | datetime     | YES  |     | NULL    |                |
    -- | account_id     | int unsigned | YES  |     | NULL    |                |
    -- | txn_type_cd    | varchar(1)   | NO   |     | NULL    |                |
    -- | amount         | double       | YES  |     | NULL    |                |
    -- +----------------+--------------+------+-----+---------+----------------+

Checking accounts are liabilities to banks, which means you credit a liability account to increase its value and debit a liability to decrease its value. You should insert the initial rows into the account table with a zero avail_balance. Then, make these iniitial deposits:

  1. Credit transaction table with an account_id column value of 123 with $500 and a txn_type_cd column value of ‘C’.
  2. Credit transaction table with an account_id column value of 789 with $75 and a txn_type_cd column value of ‘C’.

Write an update statement to set the avail_balance column values equal to the aggregate sum of the transaction table’s rows, which treats credit transacctions (those with a ‘C’ in the txn_type_cd column as a positive number and thos with a ‘D’ in the txn_type_cd column as a negative number).

Generate a unit of work to transfer $50 from account 123 to account 789. You will need to insert two rows into the transaction table and update two rows in the account table. Use the following table definitions/data:

  1. Debit transaction table with an account_id column value of 123 with $50 and a txn_type_cd column value of ‘D’.
  2. Credit transaction table with an account_id column value of 789 with $50 and a txn_type_cd column value of ‘C’.

Apply the prior update statement to set the avail_balance column values equal to the aggregate sum of the transaction table’s rows, which treats credit transacctions (those with a ‘C’ in the txn_type_cd column as a positive number and thos with a ‘D’ in the txn_type_cd column as a negative number).

Here’s the solution to the problem:

-- +--------------------+--------------+------+-----+---------+----------------+
-- | Field              | Type         | Null | Key | Default | Extra          |
-- +--------------------+--------------+------+-----+---------+----------------+
-- | account_id         | int unsigned | NO   | PRI | NULL    | auto_increment |
-- | avail_balance      | double       | NO   |     | NULL    |                |
-- | last_activity_date | datetime     | NO   |     | NULL    |                |
-- +--------------------+--------------+------+-----+---------+----------------+
 
DROP TABLE IF EXISTS account, transaction;
 
CREATE TABLE account
( account_id          int unsigned PRIMARY KEY AUTO_INCREMENT
, avail_balance       double       NOT NULL
, last_activity_date  datetime     NOT NULL )
 ENGINE=InnoDB 
 AUTO_INCREMENT=1001 
 DEFAULT CHARSET=utf8mb4 
 COLLATE=utf8mb4_0900_ai_ci;
 
-- +----------------+--------------+------+-----+---------+----------------+
-- | Field          | Type         | Null | Key | Default | Extra          |
-- +----------------+--------------+------+-----+---------+----------------+
-- | txn_id         | int unsigned | NO   | PRI | NULL    | auto_increment |
-- | txn_date       | datetime     | YES  |     | NULL    |                |
-- | account_id     | int unsigned | YES  |     | NULL    |                |
-- | txn_type_cd    | varchar(1)   | NO   |     | NULL    |                |
-- | amount         | double       | YES  |     | NULL    |                |
-- +----------------+--------------+------+-----+---------+----------------+
 
CREATE TABLE transaction
( txn_id         int unsigned  PRIMARY KEY AUTO_INCREMENT
, txn_date       datetime      NOT NULL
, account_id     int unsigned  NOT NULL
, txn_type_cd    varchar(1)
, amount         double
, CONSTRAINT transaction_fk1 FOREIGN KEY (account_id)
 REFERENCES account(account_id))
 ENGINE=InnoDB
 AUTO_INCREMENT=1001
 DEFAULT CHARSET=utf8mb4
 COLLATE=utf8mb4_0900_ai_ci;
 
-- Insert initial accounts.
INSERT INTO account
( account_id
, avail_balance
, last_activity_date )
VALUES
( 123
, 0
,'2019-07-10 20:53:27');
 
INSERT INTO account
( account_id
, avail_balance
, last_activity_date )
VALUES
( 789
, 0
,'2019-06-22 15:18:35');
 
-- Insert initial deposits.
INSERT INTO transaction
( txn_date
, account_id
, txn_type_cd
, amount )
VALUES
( CAST(NOW() AS DATE)
, 123
,'C'
, 500 );
 
INSERT INTO transaction
( txn_date
, account_id
, txn_type_cd
, amount )
VALUES
( CAST(NOW() AS DATE)
, 789
,'C'
, 75 );
 
UPDATE account a
SET    a.avail_balance = 
 (SELECT  SUM(
            CASE
              WHEN t.txn_type_cd = 'C' THEN amount
              WHEN t.txn_type_cd = 'D' THEN amount * -1
            END) AS amount
 FROM     transaction t
 WHERE    t.account_id = a.account_id
 AND      t.account_id IN (123,789)
 GROUP BY t.account_id);
 
SELECT * FROM account;
SELECT * FROM transaction;
 
-- Insert initial deposits.
INSERT INTO transaction
( txn_date
, account_id
, txn_type_cd
, amount )
VALUES
( CAST(NOW() AS DATE)
, 123
,'D'
, 50 );
 
INSERT INTO transaction
( txn_date
, account_id
, txn_type_cd
, amount )
VALUES
( CAST(NOW() AS DATE)
, 789
,'C'
, 50 );
 
UPDATE account a
SET    a.avail_balance = 
 (SELECT  SUM(
            CASE
              WHEN t.txn_type_cd = 'C' THEN amount
              WHEN t.txn_type_cd = 'D' THEN amount * -1
            END) AS amount
 FROM     transaction t
 WHERE    t.account_id = a.account_id
 AND      t.account_id IN (123,789)
 GROUP BY t.account_id);
 
SELECT * FROM account;
SELECT * FROM transaction;

The results are:

+------------+---------------+---------------------+
| account_id | avail_balance | last_activity_date  |
+------------+---------------+---------------------+
|        123 |           450 | 2019-07-10 20:53:27 |
|        789 |           125 | 2019-06-22 15:18:35 |
+------------+---------------+---------------------+
2 rows in set (0.00 sec)
 
+--------+---------------------+------------+-------------+--------+
| txn_id | txn_date            | account_id | txn_type_cd | amount |
+--------+---------------------+------------+-------------+--------+
|   1001 | 2024-04-01 00:00:00 |        123 | C           |    500 |
|   1002 | 2024-04-01 00:00:00 |        789 | C           |     75 |
|   1003 | 2024-04-01 00:00:00 |        123 | D           |     50 |
|   1004 | 2024-04-01 00:00:00 |        789 | C           |     50 |
+--------+---------------------+------------+-------------+--------+
4 rows in set (0.00 sec)

As always, I hope this helps those trying to understand how CTEs can solve problems that would otherwise be coded in external imperative languages like Python.

Written by maclochlainn

April 1st, 2024 at 12:32 am

Ruby+MySQL on Ubuntu

without comments

This post goes through installing and configuring Ruby and Ruby on Rails for MySQL. The first step requires updating the Ubuntu OS:

sudo apt-get update

Interestingly, I found that the man-db service had inadvertently stopped. It raised the following error:

E: dpkg was interrupted, you must manually run 'sudo dpkg --configure -a' to correct the problem.

You run this command to find the problem with the dpkg utility:

sudo dpkg --configure -a

It returned:

Setting up man-db (2.10.2-1) ...
Updating database of manual pages ...
man-db.service is a disabled or a static unit not running, not starting it.

The following command started the man-db service:

sudo systemctl start man-db.service

Next, you install the prerequisite packages with this command:

sudo apt-get install -y git-core zlib1g-dev build-essential libssl-dev libreadline-dev libyaml-dev libsqlite3-dev sqlite3 libxml2-dev libxslt1-dev libcurl4-openssl-dev software-properties-common libffi-dev

Use the cd command to change to the student home directory. Clone the asdf as the multiple runtime version manager with this command:

git clone https://github.com/excid3/asdf.git ~/.asdf

The following is the output of the git clone command:

Cloning into '/home/student/.asdf'...
remote: Enumerating objects: 8756, done.
remote: Counting objects: 100% (829/829), done.
remote: Compressing objects: 100% (476/476), done.
remote: Total 8756 (delta 428), reused 657 (delta 334), pack-reused 7927
Receiving objects: 100% (8756/8756), 3.10 MiB | 4.29 MiB/s, done.
Resolving deltas: 100% (5148/5148), done.

Next, you fix your .bashrc file by adding the following components:

echo '. "$HOME/.asdf/asdf.sh"' >> ~/.bashrc
echo '. "$HOME/.asdf/completions/asdf.bash"' >> ~/.bashrc
echo 'legacy_version_file = yes' >> ~/.asdfrc
echo 'export EDITOR="code --wait"' >> ~/.bashrc

Source the modifies shell, which you can do like this:

exec $SHELL

or, like:

. ${HOME}/.bashrc

Add the following asdf plug-ins:

asdf plugin add ruby
asdf plugin add nodejs

Install Ruby with the following command:

asdf install ruby 3.3.0

Install Ruby Global with this syntax:

asdf global ruby 3.3.0

Update the Ruby Gems with this command:

gem update --system

You can confirm your Ruby install with two commands. First, use the which utility to check the Ruby install:

which -a ruby

It should return:

/home/student/.asdf/shims/ruby

Then, check the Ruby version:

ruby -v

It should return:

ruby 3.3.0 (2023-12-25 revision 5124f9ac75) [x86_64-linux]

Assuming you’ve installed and configured MySQL 8 on Ubuntu, you need this additional library to support the necessary Ruby Gem:

sudo apt-get install -y libmysqlclient-dev

Now, you can install the current MySQL Ruby Gem:

gem install mysql2

You can now write a mysql_connection.rb program to verify a connection to the MySQL 8 database, like:

# Include Ruby Gem libraries.
require 'rubygems'
require 'mysql2'
 
begin
  # Create new database connection.
  db = Mysql2::Client.new( :host     => 'localhost' \
                         , :username => 'student'   \
                         , :password => 'student'   \
                         , :database => 'studentdb')
 
  # Create a result set.
  stmt = db.query('SELECT version() AS version')
 
  # Read through the result set hash.
  stmt.each do | row |
    puts "#{row['version']}"
  end
  # Release the result set resources.
  stmt.free
 
rescue Mysql2::Error => e
  # Print the error.
  puts "ERROR #{e.errno} (#{e.sqlstate}): #{e.error}"
  puts "Can't connect to the MySQL database specified."
  # Signal an error.
  exit 1
 
ensure
  # Close the connection when it is open.
  db.close if db
end

Call the program with this syntax:

ruby mysql_connection.rb

It should return:

Connected to the MySQL database server.

You can verify the version with this mysql_version.rb program:

# Include Ruby Gem libraries.
require 'rubygems'
require 'mysql2'
 
begin
  # Create new database connection.
  db = Mysql2::Client.new( :host     => 'localhost' \
                         , :username => 'student'   \
                         , :password => 'student'   \
                         , :database => 'studentdb')
 
  # Create a result set.
  rs = db.query('SELECT version() AS version')
 
  # Read through the result set hash.
  rs.each do | row |
    puts "#{row['version']}"
  end
 
  # Release the result set resources.
  rs.free
 
rescue Mysql2::Error => e
  # Print the error.
  puts "ERROR #{e.errno} (#{e.sqlstate}): #{e.error}"
  puts "Can't connect to the MySQL database specified."
  # Signal an error.
  exit 1
 
ensure
  # Close the connection when it is open.
  db.close if db
end

On Ubuntu, it should return:

8.0.35-0ubuntu0.22.04.1

If you don’t know anything about the mysql2 Ruby Gem, you should read the documentation. It’s very concise and requires a basic understanding of Ruby programming. The two specific pages who may want to check for the next examples are:

The mysql_version.rb version uses the known string literal for columns or column aliases returned by the SQL statement, which becomes the stmt (or statement) in the program. The next program eliminates the need to enumerate with the text-based columns from the query by using the Statement#fields array values by use of a numeric index. The numeric index returns the field names from the Statement#fields class to use in as the name for values in the Result#fields value found in the row variable of the for loop.

# Include Ruby Gem libraries.
require 'rubygems'
require 'mysql2'
 
# Begin block.
begin
  # Create a new connection resource.
  db = Mysql2::Client.new( :host     => 'localhost' \
                         , :username => 'student'   \
                         , :password => 'student'   \
                         , :database => 'studentdb')
 
  # Create a result set.
  stmt = db.query("SELECT   DISTINCT i.item_title, ra.rating " +       \
                  "FROM     item i INNER JOIN rating_agency ra " +     \
                  "ON       i.item_rating_id = ra.rating_agency_id " + \
                  "WHERE    ra.rating_agency = 'MPAA'" +               \
                  "ORDER BY 1")
 
  # Read through the result set hash.
  stmt.each do | row |
    out = ""
    i = 0
    while i < stmt.fields.count()
      # Check when not last column and use the:
      #   - Hash returned by the result set for the value, and
      #   - String array value returned by the statement object
      #     as the name value of the hash by leveraging its 
      #     numeric index.
      if i < stmt.fields.count() - 1
        out += "#{row[stmt.fields[i]]}"
        out += ", "
      else
        out += "#{row[stmt.fields[i]]}"
      end
      i += 1
    end
    puts "#{out}"
  end
 
  # Release the result set resources.
  stmt.free
 
rescue Mysql2::Error => e
  # Print the error.
  puts "ERROR #{e.errno} (#{e.sqlstate}): #{e.error}"
  puts "Can't connect to MySQL database specified."
  # Signal an error.
  exit 1
 
ensure
  # Close the connection when it is open.
  db.close if db
end

It returns the select two columns from the query:

A Man for All Seasons, G
Around the World in 80 Days, G
Beau Geste, PG
Brave Heart, R
Camelot, G
Casino Royale, PG-13
...
Tomorrow Never Dies, PG-13
Tora! Tora! Tora!, G
Tron, PG

The following mysql_query_params.rb Ruby example accepts a single argument to leverage a wild card query in MySQL:

require 'rubygems'
require 'mysql2'
 
# Input external arguments.
arguments = ARGV
 
# Check for one input parameter and substitute an empty string
# when one isn't found.
if arguments.length == 1
  argument = arguments[0]
else
  argument = ""
end
 
# Begin block.
begin
  # Create a new connection resource.
  db = Mysql2::Client.new( :host     => 'localhost' \
                         , :username => 'student'   \
                         , :password => 'student'   \
                         , :database => 'studentdb')
 
  # Create a result set.
  stmt = db.prepare("SELECT   DISTINCT i.item_title, ra.rating " +       \
                    "FROM     item i INNER JOIN rating_agency ra " +     \
                    "ON       i.item_rating_id = ra.rating_agency_id " + \
                    "WHERE    ra.rating_agency = 'MPAA'" +               \
                    "AND      i.item_title LIKE CONCAT(?,'%')" +         \
                    "ORDER BY 1")
 
  # Bind the variable into the query.
  rs = stmt.execute(argument)
 
  # Read through the result set hash.
  rs.each do | row |
    out = ""
    i = 0
    while i < rs.fields.count()
      # Check when not last column and use the:
      #   - Hash returned by the result set for the value, and
      #   - String array value returned by the statement object
      #     as the name value of the hash by leveraging its 
      #     numeric index.
      if i < rs.fields.count() - 1
        out += "#{row[rs.fields[i]]}"
        out += ", "
      else
        out += "#{row[rs.fields[i]]}"
      end
      i += 1
    end
    puts "#{out}"
  end
 
  # Release the result set resources.
  rs.free
 
rescue Mysql2::Error => e
  # Print the error.
  puts "ERROR #{e.errno} (#{e.sqlstate}): #{e.error}"
  puts "Can't connect to MySQL database specified."
  # Signal an error.
  exit 1
 
ensure
  # Close the connection when it is open.
  db.close if db
end

If you call the mysql_query_params.rb program with this syntax:

ruby mysql_aquery_params.rb Harry

It’ll return the following from the studentdb database:

Harry Potter and the Chamber of Secrets, PG
Harry Potter and the Deathly Hallows, Part 1, PG-13
Harry Potter and the Deathly Hallows, Part 2, PG-13
Harry Potter and the Goblet of Fire, PG-13
Harry Potter and the Half Blood Prince, PG
Harry Potter and the Order of the Phoenix, PG-13
Harry Potter and the Prisoner of Azkaban, PG
Harry Potter and the Sorcerer's Stone, PG

After that, you should install Rails (check for current version beyond 1/2024). Install Ruby Global with this syntax:

gem install rails -v 7.1.3

Check the version installed:

rails -v

It should return:

Rails 7.1.3

Run this command to enable Rails for MySQL 8:

rails new myapp -d mysql

If you want to configure a username and password for MySQL, edit the config/database.yml file.

As always, I hope this helps somebody looking for step-by-step guide.

Written by maclochlainn

February 3rd, 2024 at 4:57 pm

Ubuntu, Perl & MySQL

without comments

Configuring Perl to work with MySQL is straight forward. While Perl is installed generally, you may need to install the libdbd-mysql-perl library.

You install it as a sudoer user with this syntax:

sudo apt install -y libdbd-mysql-perl

You can find the Perl version with the following version.pl program:

1
2
3
4
#!/usr/bin/perl -w
 
# Print the version.
print "Perl ".$]."\n";

The first line lets you call the program without prefacing the program name with perl. The first line invokes a subshell of perl by default. You just need to ensure the file has read and execute privileges to run by using the

chmod 755 version.pl

You call it with this:

./version.pl

It prints:

Perl 5.034000

The following static_query.pl Perl program uses the Perl DBI library to query and return a data set based on a static query.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
#!/usr/bin/perl -w
 
# Use the DBI library.
use DBI;
use strict;
use warnings;
 
# Create a connection.
my $dbh = DBI->connect("DBI:mysql:database=studentdb;host=localhost:3306"
                      ,"student","student",{'RaiseError' => 1});
 
# Create SQL statement.
my $sql = "SELECT i.item_title
           ,      ra.rating
           ,      cl.common_lookup_meaning
           FROM   item i INNER JOIN common_lookup cl
           ON     i.item_type = cl.common_lookup_id INNER JOIN rating_agency ra
           ON     i.item_rating_id = ra.rating_agency_id
           WHERE  i.item_title LIKE 'Harry%'
           AND    cl.common_lookup_type = 'BLU-RAY'";
 
# Prepare SQL statement.
my $sth = $dbh->prepare($sql);
 
# Execute statement and read result set.
$sth->execute() or die $DBI::errstr;
 
# Read through returned rows, assign elements explicitly to match SELECT-list.
while (my @row = $sth->fetchrow_array()) {
  my $item_title = $row[0];
  my $rating = $row[1];
  my $lookup_meaning = $row[2];
  print "$item_title, $rating, $lookup_meaning\n";
}
 
# Close resources.
$sth->finish();

It returns the following rows from the sample database:

Harry Potter and the Sorcerer's Stone, PG, Blu-ray
Harry Potter and the Chamber of Secrets, PG, Blu-ray
Harry Potter and the Prisoner of Azkaban, PG, Blu-ray
Harry Potter and the Goblet of Fire, PG-13, Blu-ray

The following dynamic_query.pl Perl program uses the Perl DBI library to prepare a query, bind a local variable into the query, and return a data set based on a dynamic query.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
#!/usr/bin/perl -w
 
# Use the DBI library.
use DBI;
use strict;
use warnings;
 
# Mimic a function parameter by using a local variable.
my $item_title_in = 'Star';
 
# Create a connection.
my $dbh = DBI->connect("DBI:mysql:database=studentdb;host=localhost:3306"
                      ,"student","student",{'RaiseError' => 1});
 
# Create SQL statement.
my $sql = "SELECT i.item_title
           ,      ra.rating
           ,      cl.common_lookup_meaning
           FROM   item i INNER JOIN common_lookup cl
           ON     i.item_type = cl.common_lookup_id INNER JOIN rating_agency ra
           ON     i.item_rating_id = ra.rating_agency_id
           WHERE  i.item_title LIKE CONCAT(?,'%')
           AND    cl.common_lookup_type = 'BLU-RAY'";
 
# Prepare SQL statement.
my $sth = $dbh->prepare($sql);
 
# Bind a variable to first parameter in the query string.
$sth->bind_param(1, $item_title_in);
 
# Execute statement and read result set.
$sth->execute() or die $DBI::errstr;
 
# Read through returned rows, assign elements explicitly to match SELECT-list.
while (my @row = $sth->fetchrow_array()) {
  my $item_title = $row[0];
  my $rating = $row[1];
  my $lookup_meaning = $row[2];
  print "$item_title, $rating, $lookup_meaning\n";
}
 
# Close resources.
$sth->finish();

It returns the following rows from the sample database:

Star Wars II, PG, Blu-ray

You can replace lines 34 through 40 with the following to read any number of columns into a comma-delimited row return:

34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
# Read through returned rows, assign elements explicitly to match SELECT-list.
while (my @row = $sth->fetchrow_array()) {
 
  # Read through a dynamic column list for column separated display.
  my $result = '';
  foreach(@row) {
    if (length($result) == 0) {
      $result = $_; }
    else {
      $result .= ", " . $_; }
  } 
 
  # Print comma-separted values by row.
  print $result . "\n"
}

It returns the following rows from the sample database:

Star Wars II, PG, Blu-ray

As always, I hope this helps the reader solve a problem.

Written by maclochlainn

January 8th, 2024 at 10:37 pm

MySQL RegExp Default

with 4 comments

We had an interesting set of questions regarding the REGEXP comparison operator in MySQL today in both sections of Database Design and Development. They wanted to know the default behavior.

For example, we built a little movie table so that we didn’t change their default sakila example database. The movie table was like this:

CREATE TABLE movie
( movie_id     int unsigned primary key auto_increment
, movie_title  varchar(60)) auto_increment=1001;

Then, I inserted the following rows:

INSERT INTO movie 
( movie_title )
VALUES
 ('The King and I')
,('I')
,('The I Inside')
,('I am Legend');

Querying all results with this query:

SELECT * FROM movie;

It returns the following results:

+----------+----------------+
| movie_id | movie_title    |
+----------+----------------+
|     1001 | The King and I |
|     1002 | I              |
|     1003 | The I Inside   |
|     1004 | I am Legend    |
+----------+----------------+
4 rows in set (0.00 sec)

The following REGEXP returns all the rows because it looks for a case insensitive “I” anywhere in the string.

SELECT movie_title
FROM   movie
WHERE  movie_title REGEXP 'I';

The implicit regular expression is actually:

WHERE  movie_title REGEXP '^.*I.*$';

It looks for zero-to-many of any character before and after the “I“. You can get any string beginning with an “I” with the “^I“; and any string ending with an “I” with the “I$“. Interestingly, the “I.+$” should only match strings with one or more characters after the “I“, but it returns:

+----------------+
| movie_title    |
+----------------+
| The King and I |
| The I Inside   |
| I am Legend    |
+----------------+
3 rows in set (0.00 sec)

This caught me by surprise because I was lazy. As pointed out in the comment, it only appears to substitute a “.*“, or zero-to-many evaluation for the “.+” because it’s a case-insensitive search. There’s another lowercase “i” in the “The King and I” and that means the regular expression returns true because that “i” has one-or-more following characters. If we convert it to a case-sensitive comparison with the keyword binary, it works as expected because it ignores the lowercase “i“.

WHERE  binary movie_title REGEXP '^.*I.*$';

This builds on my 10-year old post on Regular Expressions. As always, I hope these notes helps others discovering features and behaviors of the MySQL database, and Bill thanks for catching my error.

Written by maclochlainn

April 29th, 2022 at 11:50 pm

MySQL Floating Types

with 2 comments

I’m glad that testing new MySQL releases is so frequent for me. Each testing cycle let me catch warning messages about deprecated behaviors before they’re removed. This one announced the deprecation of digits for floating point data types, like double. The following column definition for a table in my code tree triggered the warning message:

, amount                DOUBLE(10,2)

MySQL 8 (8.0.21) raised the following warning message:

Warning (code 1681): Specifying number of digits for floating point data types is deprecated and will be removed in a future release.

Recognizing the deprecation, I redefined the column as:

, amount                DOUBLE

I’m glad the MySQL development team is focused on alerting us to deprecations through warning messages. Naturally, I fixed all of the tables proactively. If you want more detail you can read this MySQL web page on Problems with Floating Point Values.

Written by maclochlainn

October 8th, 2020 at 12:06 pm

Posted in MySQL,MySQL 8,sql

Tagged with ,

MySQL Provisioning

with one comment

I’ve been using MySQL 8 on Linux for a couple years but the Linux repository version didn’t install the new MySQL Shell. So, I discovered the new MySQL Shell when I installed MySQL 8 (8.0.21) on Windows to teach my student how to use it to learn SQL commands. I encourage you to read the full MySQL Shell document.

The following is a tutorial to provision a student user and studentdb database in MySQL. It uses the MySQL Shell (mysqlsh) and stages for uploads of comma-separated values files.

After installing MySQL on the Windows 10 OS, open the Window OS Command Line Interface (CLI) shell by entering the following in the search field at the bottom left:

cmd

It launches a CLI interface to the Windows OS. The cmd (command) utility opens the CLI in the following directory (where you substitute your user’s name for the username placeholder below):

C:\Users\username

At the command prompt, you would enter mysql to launch the old MySQL CLI. Instead of that, you enter mysqlsh to launch the new MySQL CLI as the root user. The command to launch the MySQL Shell as the root user is:

mysqlsh -uroot -p

It should return the following and prompt you for a single character entry to save the password for the Operating System user. As a rule, in a development instance that’s a good idea and practice.

MySQL Shell 8.0.21
 
Copyright (c) 2016, 2020, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its affiliates.
Other names may be trademarks of their respective owners.
 
Type '\help' or '\?' for help; '\quit' to exit.
Creating a session to 'root@localhost'
Please provide the password for 'root@localhost:33060': ********
Save password for 'root@localhost:33060'? [Y]es/[N]o/Ne[v]er (default No): y
Fetching schema names for autocompletion... Press ^C to stop.
Your MySQL connection id is 9 (X protocol)
Server version: 8.0.21 MySQL Community Server - GPL
No default schema selected; type \use <schema> to set one.
 MySQL  localhost:33060+ ssl  JS >

The prompt will not accept SQL commands because it always initializes in the JavaScript (JS) context. The MySQL Shell supports three interactive interfaces: JavaScript, Python, and SQL.

You can verify the integrity of the shell from the JavaScript (JS) context as the root user with the following command:

 MySQL  localhost:33060+ ssl  JS > shell.status()

As the root user, it should return something like this:

MySQL Shell version 8.0.21
 
Connection Id:                9
Default schema:
Current schema:
Current user:                 root@localhost
SSL:                          Cipher in use: TLS_AES_256_GCM_SHA384 TLSv1.3
Using delimiter:              ;
Server version:               8.0.21 MySQL Community Server - GPL
Protocol version:             X protocol
Client library:               8.0.21
Connection:                   localhost via TCP/IP
TCP port:                     33060
Server characterset:          utf8mb4
Schema characterset:          utf8mb4
Client characterset:          utf8mb4
Conn. characterset:           utf8mb4
Result characterset:          utf8mb4
Compression:                  Enabled (DEFLATE_STREAM)
Uptime:                       20 hours 4 min 19.0000 sec

You can switch to the SQL context as the root or any other user with this command. The switch only changes your form of interaction with the server and you remain connected as the root user:

 MySQL  localhost:33060+ ssl  JS > \sql

You can verify that your session is still owned by the root user with the following SELECT statement:

 MySQL  localhost:33060+ ssl  SQL > SELECT user();

It returns:

+----------------+
| user()         |
+----------------+
| root@localhost |
+----------------+
1 row in set (0.0005 sec)

The next step shows you how to setup a sample studentdb database. Some syntax has changed from prior MySQL releases. Here are the three steps:

  1. Create the studentdb database with the following command as the MySQL root user:

     MySQL  localhost:33060+ ssl  SQL > CREATE DATABASE studentdb;
  2. Grant the root user the privilege to grant to others, which root does not have by default. You use the following syntax as the MySQL root user:

     MySQL  localhost:33060+ ssl  SQL > GRANT ALL ON *.* TO 'root'@'localhost';
  3. Create the user with a clear English password and grant the user student full privileges on the studentdb database:

     MySQL  localhost:33060+ ssl  SQL > CREATE USER 'student'@'localhost' IDENTIFIED WITH mysql_native_password BY 'student';
     MySQL  localhost:33060+ ssl  SQL > GRANT ALL ON studentdb.* TO 'student'@'localhost';
  4. Our sample database uses large file uploads with MySQL’s LOAD command, which means you need to grant one additional global privilege:

     MySQL  localhost:33060+ ssl  SQL > GRANT FILE ON *.* TO 'student'@'localhost';

The MySQL FILE privilege is a global privilege to read and write files on the local server. MySQL 8 installation on Windows 10 sets the following directory as the target for uploading files in the my.ini file:

# Secure File Priv.
secure-file-priv="C:/ProgramData/MySQL/MySQL Server 8.0/Uploads"

You can find the setting in the C:\ProgramData\MySQL\MySQL Server 8.0\my.ini file. You can find this value without referencing the my.ini file by querying the data:

show variables like 'secure_file_priv';

A new installation should return:

+------------------+------------------------------------------------+
| Variable_name    | Value                                          |
+------------------+------------------------------------------------+
| secure_file_priv | C:\ProgramData\MySQL\MySQL Server 8.0\Uploads\ |
+------------------+------------------------------------------------+
1 row in set (0.2253 sec)

You can test the ability to use the LOAD command with the following avenger.csv test file. Copy it into the C:\ProgramData\MySQL\MySQL Server 8.0\Uploads directory and make sure the directory permissions are set to read-only for Everyone (check the Microsoft OS documentation if these concepts are new to you).

1,'Anthony','Stark','Iron Man'
2,'Thor','Odinson','God of Thunder'
3,'Steven','Rogers','Captain America'
4,'Bruce','Banner','Hulk'
5,'Clinton','Barton','Hawkeye'
6,'Natasha','Romanoff','Black Widow'

Open another cmd (command) CLI and put the following code into a file that you save as avenger.sql in the C:\Users\username directory.

-- Conditionally drop objects.
SELECT 'AVENGER' AS "Drop Table";
DROP TABLE IF EXISTS avenger;
 
-- Create an avenger table.
CREATE TABLE avenger
( avenger_id      INT UNSIGNED PRIMARY KEY AUTO_INCREMENT
, first_name      VARCHAR(20)
, last_name       VARCHAR(20)
, character_name  VARCHAR(20)) ENGINE=InnoDB DEFAULT=utf8;
 
-- Load the data from a file, don't forget the \n after the \r on Windows or it won't work.
LOAD DATA INFILE 'C:/ProgramData/MySQL/MySQL Server 8.0/Uploads/avenger.csv'
-- LOAD DATA INFILE 'avenger.csv'
INTO TABLE avenger
FIELDS TERMINATED BY ','
ENCLOSED BY '"'
ESCAPED BY '/'
LINES TERMINATED BY '\r\n';
 
-- Select the uploaded records.
SELECT * FROM avenger;

From the cmd (command) shell, launch the MySQL Shell as the student user with the following syntax:

mysqlsh -ustudent -p -Dstudentdb

At the MySQL Shell (mysqlsh) prompt switch from the default JavaScript (JS) context to SQL context and run the following query:

 MySQL  localhost:33060+ ssl  studentdb  SQL > \sql
 MySQL  localhost:33060+ ssl  studentdb  SQL > SELECT user(), database();

If you did everything above correctly, it should return:

+-------------------+------------+
| user()            | database() |
+-------------------+------------+
| student@localhost | studentdb  |
+-------------------+------------+
1 row in set (0.0003 sec)

Again, assuming you did everything above correctly, you should be able to run your avenger.sql script file from the MySQL Shell (mysqlsh) prompt, like:

 MySQL  localhost:33060+ ssl  studentdb  SQL > source avenger.sql

It should return output like the following:

Query OK, 0 rows affected (0.0003 sec)
+------------+
| Drop Table |
+------------+
| AVENGER    |
+------------+
1 row in set (0.0003 sec)
Query OK, 0 rows affected (0.0595 sec)
Query OK, 0 rows affected (0.0002 sec)
Query OK, 0 rows affected (0.1293 sec)
Query OK, 0 rows affected (0.0002 sec)
Query OK, 6 rows affected (0.0046 sec)
 
Records: 6  Deleted: 0  Skipped: 0  Warnings: 0
Query OK, 0 rows affected (0.0004 sec)
+------------+------------+------------+-------------------+
| avenger_id | first_name | last_name  | character_name    |
+------------+------------+------------+-------------------+
|          1 | 'Anthony'  | 'Stark'    | 'Iron Man'        |
|          2 | 'Thor'     | 'Odinson'  | 'God of Thunder'  |
|          3 | 'Steven'   | 'Rogers'   | 'Captain America' |
|          4 | 'Bruce'    | 'Banner'   | 'Hulk'            |
|          5 | 'Clinton'  | 'Barton'   | 'Hawkeye'         |
|          6 | 'Natasha'  | 'Romanoff' | 'Black Widow'     |
+------------+------------+------------+-------------------+
6 rows in set (0.0005 sec)

You now have a student user and studentdb database like my students. I hope it was fun to build.

You can find the my.ini file in the C:\ProgramData\MySQL\MySQL Server 8.0 directory of a standard Windows 10 file system. Its a good idea not to change anything unless you know what you’re doing, and remember you need to restart the Microsoft MySQL80 Service for any change to be made effective in your database operations.

Written by maclochlainn

September 28th, 2020 at 7:26 am

MySQL JSON Server

with one comment

A student question: Does JavaScript make context switching for web-based applications obsolete? Wow! I asked what that meant. He said, it means JavaScript replaces all other server-side programming languages, like PHP, C#, or Python. I asked the student why he believed that. His answer was that’s what two interviewing managers told him.

I thought it would be interesting to put the idea to a test. Below is a Node.js script that acts as a utility that queries the MySQL database with substitution variables in query. It also returns a standard out (stdout) stream of the MySQL query’s results. It also supports three flag and value pairs as arguments, and optionally writes the results of the MySQL query to a log file while still returning result as the stdout value. All errors are written to the standard error (stderr) stream.

The Node.js solution is completely portable between Windows and Linux. You can deploy it to either platform without any edits for Windows case insensitive Command-Line Interface (CLI). Clearly, Node.js offers a replacement for direct interaction with the .NET components in PowerShell. This appears to mean basic Linux shell or PowerShell knowledge is all that’s required to write and deploy JavaScript programs as server-side programming solutions. It means anything that you would have done with the .NET you can do with JavaScript. Likewise, you can replace PHP, C#, Python, or Ruby server-side scripts with JavaScript programs.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
// Declare constants. 
const fs = require('fs') 
const util = require('util') 
const express = require('express') 
const mysql = require('mysql') 
const connection = mysql.createConnection({ 
  host: 'localhost', 
  user: 'student', 
  password: 'student', 
  database: 'studentdb' 
}) 
 
// Declare local variables for case insensitive use. 
var data = '' 
var buffer = Buffer.alloc(0) 
var path = '' 
 
// Declare default query variables dates. 
var startDate = new Date('1980-01-01') 
var endDate = new Date() 
 
// Set default endDate value as tomorrow. 
endDate.setDate(new Date().getDate() + 1) 
 
// Define a regular expression for valid file names. 
var regexp = /^([0-9a-zA-Z]+|[0-9a-zA-Z]+\.+[0-9a-zA-Z]{3})$/ 
 
// Assign dynamic variables from arguments. 
var argv = process.argv.slice(2) 
 
// Check for paired values, evaluate and assign them to local variables. 
if ((argv.length % 2) == 0) { 
 for (let i = 0; i < argv.length; i += 2) { 
   // Assign a file name to write to the output path. 
   if ((argv[i].toLowerCase() == '-f') && (regexp.test(argv[i+1]))) { 
     // Assign present working for Windows or Linux. 
     if (process.platform == 'win32') 
       path = '.\\' + argv[1] 
     else 
       path = './' + argv[1] 
   } 
   // Assign a start date from the input string. 
   else if (argv[i].toLowerCase() == '-b') { 
     startDate = new Date(argv[i+1]) 
   } 
   // Assign a end date from the input string. 
   else if (argv[i].toLowerCase() == '-e') { 
     endDate = new Date(argv[i+1]) 
   } 
 } 
} 
else { 
 console.error('Arguments must be in pairs: flag and value.') 
} 
 
// Define and run MySQL query. 
connection.query("SELECT   i.item_title " + 
                 ",        date_format(i.release_date,'%d-%M-%Y') AS release_date " + 
                 "FROM     item i JOIN common_lookup cl " + 
                 "ON       i.item_type = cl.common_lookup_id " + 
                 "WHERE    cl.common_lookup_type = 'BLU-RAY' " + 
                 "AND      i.release_date BETWEEN ? AND ? " + 
                 "ORDER BY i.release_date" 
                ,[startDate, endDate], function (err, result) { 
 if (err) { 
   console.error('Query contains error ...') 
   console.error('-> ' + err) 
 } 
 else { 
   // Prints the index value in the RowDataPacket. 
   for(let element in result) { 
     data += result[element].item_title + ', ' + result[element].release_date + '\n' 
   } 
   // Write file when data string is not empty. 
   if (data.length > 0 ) { 
     buffer = Buffer.alloc(data.length,data) 
 
     // Check for a defined path before writing a file. 
     if (path.length > 0) { 
       // Open the file. 
       fs.open(path, 'w', function(err, fd) { 
         if (err) { 
           console.error('Could not open [' + path + '] file [' + err + ']') 
         } 
         else { 
           // Write the file. 
           fs.write(fd, buffer, 0, buffer.length, null, function(err) { 
             if (err) 
               console.error('Error writing [' + path + '] file [' + err + ']') 
             fs.close(fd, function() { 
               if (fs.existsSync(path)) { 
                 process.exit(0) 
               } 
             }) 
           }) 
         }   
       }) 
     } 
     // Set standard out (stdout). 
     console.log(data) 
   } 
   else { 
     console.error('Query returned no rows.') 
   } 
 } 
}) 
 
// Close MySQL connection. 
connection.end()

You can call this code with the default values, like

node app.js

You can call this code with a user defined file name, and a custom start and end date values, like

node app.js -f output.csv -b '2001-01-01' -e '2004-12-31'

The latter command returns the following by querying my MySQL studentdb video store:

Star Wars II, 16-May-2002 
Harry Potter and the Chamber of Secrets, 28-May-2002 
Harry Potter and the Sorcerer's Stone, 28-May-2002 
Die Another Day, 03-June-2003 
Harry Potter and the Prisoner of Azkaban, 23-October-2004

As always, I hope this helps somebody trying to sort it out.

Written by maclochlainn

August 1st, 2020 at 1:05 am

MySQL Insert from Query

with 4 comments

While working with an error that my students surfaced in the Oracle Database 12c, I blogged about the limit of using a subquery in an Oracle INSERT statement, and I discovered something when retesting it in MySQL. It was a different limitation. I was also surprised when I didn’t find any mention of it through a Google search, but then I may just not have the right keywords.

The original test case uses a subquery to create a multiple row result set for an INSERT statement. Unfortunately, I discovered that you can’t always embed a UNION or UNION ALL inside a subquery. At least, you can’t when you call the subquery inside an INSERT statement. For example, let’s create a DESTINATION table and then we’ll try to insert records with a query that fabricates a result set.

-- Drop the destination table.
DROP TABLE IF EXISTS destination;
 
-- Create the destination table.
CREATE TABLE destination
( destination_id    int unsigned
, destination_name  varchar(30));

Now let’s try the subquery:

1
2
3
4
INSERT INTO destination
( SELECT 1,'Sample1'
  UNION ALL
  SELECT 2,'Sample2' );

It raises the following error message:

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'UNION ALL
  SELECT 2,'Sample2' )' at line 3

I wasn’t sure if I missed something. It turned out that I did. While you can put a subquery inside an INSERT statement, you can’t embed it inside a set of parentheses when it contains a UNION ALL set operator. Other statements work with or without parentheses.

1
2
3
4
INSERT INTO destination
  SELECT 1,'Sample1'
  UNION ALL
  SELECT 2,'Sample2';

If somebody has any more to add, I look forward to reading it.

Written by maclochlainn

June 15th, 2014 at 12:19 am

Posted in MySQL,sql

Tagged with