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Title Case Anyone?

Sometimes life is too surreal. Like when somebody says, “How do you get title case in an Oracle database?” That’s when you know three things about the individual, while suppressing laughter. They’re not very experienced with SQL, likely lazy, and don’t read the documentation.

I had a little fun with somebody today by taking them down a small rat-hole. “Oh, gosh … ” I said, “… let’s write a function for that.” Here’s the joke function, like:

CREATE OR REPLACE
FUNCTION title_case
( string VARCHAR2 ) RETURN VARCHAR2 IS
BEGIN
  /* Change upper case to title case. */
  RETURN UPPER(SUBSTR(string,1,1)) || LOWER(SUBSTR(string,2,LENGTH(string)));
END title_case;
/

Then, we tested it with a query from the pseudo dual table:

SELECT title_case('incredible') AS "Proper Name" FROM dual;

It returned:

Proper Name
----------
Incredible

Then, I said “Oh, that’s not his proper name in the Pixar World.” It should be: Mr. Incredible. Let’s try that:

SELECT title_case('mr. incredible') AS "Proper Name" FROM dual;

It returned:

Proper Name
--------------
Mr. incredible

Then, I said: “That’s not what we want at all. Should we rewrite our function or simply use the INITCAP built-in function?” Then, I wrote:

SELECT INITCAP('mr. incredible') AS "Proper Name" FROM dual;

It returned:

Proper Name
--------------
Mr. Incredible

Well, needless to say my acquaintance got it immediately and said “I should have Googled it or read the documentation.” I concurred with his observation.

Just sharing a cute day’s event that made me laugh and cry at the same time because there are too many who say SQL isn’t worth learning.

Written by maclochlainn

June 30th, 2021 at 11:49 am

Posted in Linux,MySQL,MySQL 8,Oracle,Oracle 18c,sql,Unix,Windows 10

Tagged with MySQL Developer, Oracle Developer

MySQL PHP Transaction

without comments

My students liked the MySQL Transaction post but wanted one that showed how an external web application would interact with MySQL in the scope of a transaction. So, I put a little PHP function together that write across two related tables in the context of a transaction. It uses mysqli (MySQL Improved Extension) to connect PHP to the MySQL database.

The function is barebones and uses the oldest approach of hidden inputs to maintain context between rendered forms using an HTML POST method. The hidden inputs are preceded with “h_” and snake case is used for variable names.

The function only writes to two tables. It writes to the member table and when that completes successfully to the contact table. The function:

Submits credentials from a file and raises an error when they don’t work.
Initializes a SQL statement.
Disables auto commit.
Starts a transaction.
Defines a first SQL statement with placeholders.
Binds local variables to the first SQL statement’s placeholders.
Rolls back the transaction when the first statement fails and continues to the next SQL statement when first statement succeeds.
Defines a second SQL statement with placeholders.
Binds local variables to the second SQL statement’s placeholders.
Rolls back the transaction when the second statement fails and commits the work when the second statement succeeds.
Closes a SQL statement.

The code for the PHP function is:

/*
||  Function Name: update_membership
|| ----------------------------------------------------------------------
||  No return, treated as a procedure, or method returning a void.
|| ----------------------------------------------------------------------
*/
function update_membership(
    $h_account_number
  , $h_member_type
  , $h_credit_card_number
  , $h_credit_card_type
  , $account_number
  , $member_type
  , $credit_card_number
  , $credit_card_type
  , $h_first_name
  , $h_middle_name
  , $h_last_name
  , $h_contact_type
  , $first_name
  , $middle_name
  , $last_name
  , $contact_type) {
 
  // Include the credentials file if omitted.
  include_once("MySQLCredentials.inc");
 
  // Assign credentials to connection.
  $mysqli = new mysqli(HOSTNAME, USERNAME, PASSWORD, DATABASE);
 
  // Check for connection error and print message.
  if ($mysqli->connect_errno) {
    print $mysqli->connect_error."<br />";
    print "Connection not established ...<br />";
  }
  else {
    // Initial statement.
    $stmt = $mysqli->stmt_init();
 
    // Disable auto commit when you want two plus statements run.
    $mysqli->autocommit(FALSE);
 
    // Set the transaction guarantee.
    $mysqli->begin_transaction(MYSQLI_TRANS_START_READ_WRITE);
 
    // Declare a static query.
    $sql = "UPDATE   member\n"
         . "SET      member_type = ?\n"
         . ",        credit_card_number = ?\n"
         . ",        credit_card_type = ?\n"
         . "WHERE    account_number = ?\n"
         . "AND      member_type = ?\n"
         . "AND      credit_card_number = ?\n"
         . "AND      credit_card_type = ?\n";
 
    // Prepare statement.
    if ($stmt->prepare($sql)) {
      $stmt->bind_param(
          "sssssss"
         , $member_type
         , $credit_card_number
         , $credit_card_type
         , $account_number
         , $h_member_type
         , $h_credit_card_number
         , $h_credit_card_type); } 
 
    // Attempt query and exit with failure before processing.
    if (!$stmt->execute()) {
 
      // Rollback or undo the transaction.
      $mysqli->rollback();
 
      // Print failure to resolve query message.
      print $mysqli->error."<br />\n";
      print "Failed to resolve query ...<br />\n";
    }
 
    // Declare a static query.
    $sql = "UPDATE   contact\n"
         . "SET      first_name = ?\n"
         . ",        middle_name = ?\n"
         . ",        last_name = ?\n"
         . ",        contact_type = ?\n"
         . "WHERE    first_name = ?\n"
         . "AND      middle_name = ?\n"
         . "AND      last_name = ?\n"
         . "AND      contact_type = ?\n";
 
    // Prepare statement.
    if ($stmt->prepare($sql)) {
      $stmt->bind_param(
          "ssssssss"
        , $first_name
        , $middle_name
        , $last_name
        , $contact_type
        , $h_first_name
        , $h_middle_name
        , $h_last_name
        , $h_contact_type); } 
 
    // Attempt query and exit with failure before processing.
    if (!$stmt->execute()) {
 
      // Rollback or undo the transaction.
      $mysqli->rollback();
 
      // Print failure to resolve query message.
      print $mysqli->error."<br />";
      print "Failed to resolve query ...<br />";
    }
    else {   
      /*  Manually commiting writes when you have disabled the
      ||  default auto commit setting, explained above.
      || ------------------------------------------------------------
      ||  You would add the following command to commit the 
      ||  transaction.
      ||  ------------------------------
      ||   $mysqli->commit();
      || ------------------------------------------------------------
      */
      $mysqli->commit();
 
      // Close the transaction.
      $mysqli->close();
    }
  }
}

/* || Function Name: update_membership || ---------------------------------------------------------------------- || No return, treated as a procedure, or method returning a void. || ---------------------------------------------------------------------- */ function update_membership( $h_account_number , $h_member_type , $h_credit_card_number , $h_credit_card_type , $account_number , $member_type , $credit_card_number , $credit_card_type , $h_first_name , $h_middle_name , $h_last_name , $h_contact_type , $first_name , $middle_name , $last_name , $contact_type) { // Include the credentials file if omitted. include_once("MySQLCredentials.inc"); // Assign credentials to connection. $mysqli = new mysqli(HOSTNAME, USERNAME, PASSWORD, DATABASE); // Check for connection error and print message. if ($mysqli->connect_errno) { print $mysqli->connect_error." "; print "Connection not established ... "; } else { // Initial statement. $stmt = $mysqli->stmt_init(); // Disable auto commit when you want two plus statements run. $mysqli->autocommit(FALSE); // Set the transaction guarantee. $mysqli->begin_transaction(MYSQLI_TRANS_START_READ_WRITE); // Declare a static query. $sql = "UPDATE member\n" . "SET member_type = ?\n" . ", credit_card_number = ?\n" . ", credit_card_type = ?\n" . "WHERE account_number = ?\n" . "AND member_type = ?\n" . "AND credit_card_number = ?\n" . "AND credit_card_type = ?\n"; // Prepare statement. if ($stmt->prepare($sql)) { $stmt->bind_param( "sssssss" , $member_type , $credit_card_number , $credit_card_type , $account_number , $h_member_type , $h_credit_card_number , $h_credit_card_type); } // Attempt query and exit with failure before processing. if (!$stmt->execute()) { // Rollback or undo the transaction. $mysqli->rollback(); // Print failure to resolve query message. print $mysqli->error." \n"; print "Failed to resolve query ... \n"; } // Declare a static query. $sql = "UPDATE contact\n" . "SET first_name = ?\n" . ", middle_name = ?\n" . ", last_name = ?\n" . ", contact_type = ?\n" . "WHERE first_name = ?\n" . "AND middle_name = ?\n" . "AND last_name = ?\n" . "AND contact_type = ?\n"; // Prepare statement. if ($stmt->prepare($sql)) { $stmt->bind_param( "ssssssss" , $first_name , $middle_name , $last_name , $contact_type , $h_first_name , $h_middle_name , $h_last_name , $h_contact_type); } // Attempt query and exit with failure before processing. if (!$stmt->execute()) { // Rollback or undo the transaction. $mysqli->rollback(); // Print failure to resolve query message. print $mysqli->error." "; print "Failed to resolve query ... "; } else { /* Manually commiting writes when you have disabled the || default auto commit setting, explained above. || ------------------------------------------------------------ || You would add the following command to commit the || transaction. || ------------------------------ || $mysqli->commit(); || ------------------------------------------------------------ */ $mysqli->commit(); // Close the transaction. $mysqli->close(); } } }

Line 41 disables auto commit and line 44 starts the transaction. Each statement is managed with the subsequent statement nested inside a block of code that is only reachable when the prior statement succeeds. While this only uses the member and contact table, it could use any number of tables. The natural alternative is building an updatable view.

As always, I hope this helps anybody looking for a code complete example.

Written by maclochlainn

June 29th, 2021 at 5:23 pm

Posted in LAMP,Linux,MySQL,MySQL 8,mysqli,sql

Tagged with MySQL DBA, MySQL Developer

SQL Handling Nulls

without comments

Interesting questions always come via my students. For example, “Why does the selective aggregation sample return null values as totals from the SUM() function in MySQL?”

First, here’s the code to build the sample table for the problem:

DROP TABLE IF EXISTS transaction;
CREATE TABLE transaction
( transaction_id      int unsigned primary key auto_increment
, transaction_date    date
, transaction_amount  double );
 
INSERT INTO transaction
( transaction_date, transaction_amount )
VALUES
 ('2021-01-10', 56)
,('2021-02-14',23.02)
,('2021-03-31',31.06)
,('2021-01-01',.25)
,('2020-01-02', 52)
,('2020-02-08',22.02)
,('2020-03-26',32.06)
,('2020-01-12',.75);;

Now, here’s the selective aggregation query:

SELECT   EXTRACT(YEAR FROM transaction_date) AS "Year"
,        SUM(
           CASE
             WHEN EXTRACT(MONTH FROM transaction_date) = 1 THEN transaction_amount
            END) AS "Jan"
,        SUM(
           CASE
             WHEN EXTRACT(MONTH FROM transaction_date) = 2 THEN transaction_amount
           END) AS "Feb"
,        SUM(
           CASE
             WHEN EXTRACT(MONTH FROM transaction_date) = 3 THEN transaction_amount
           END) AS "Mar"
,        SUM(
           CASE
             WHEN EXTRACT(MONTH FROM transaction_date) IN (1,2,3) THEN transaction_amount
           END) AS "1FQ"
FROM     transaction
WHERE    transaction_date BETWEEN '2020-01-15' AND '2021-03-15'
GROUP BY EXTRACT(YEAR FROM transaction_date)
ORDER BY 1;

It produces the following correct results (at least in response to the query above):

+------+-------+-------+-------+-------+
| Year | Jan   | Feb   | Mar   | 1FQ   |
+------+-------+-------+-------+-------+
| 2020 |  NULL | 22.02 | 32.06 | 54.08 |
| 2021 | 56.25 | 23.02 |  NULL | 79.27 |
+------+-------+-------+-------+-------+
2 rows in set (0.02 sec)

Why do you get null values for January 2020 and March 2021? That’s because the query returns null values when the conditions in the SELECT-list aren’t met for a row return. This happens:

When a row is returned for the month of February or March a null is returned in the January column.
When a row is returned for the month of January or March a null is returned in the February column.
When a row is returned for the month of January or February a null is returned in the March column.

That means there needs to be an ELSE clause in each of the CASE statements that sets the return value to zero. For example, the following query includes the ELSE clause and some nice formatting tricks:

SELECT   EXTRACT(YEAR FROM transaction_date) AS "Year"
,        CONCAT('$',LPAD(FORMAT(SUM(
           CASE
             WHEN EXTRACT(MONTH FROM transaction_date) = 1 THEN transaction_amount
             ELSE 0
            END),2),8,' ')) AS "Jan"
,        LPAD(FORMAT(SUM(
           CASE
             WHEN EXTRACT(MONTH FROM transaction_date) = 2 THEN transaction_amount
             ELSE 0
           END),2),8,' ') AS "Feb"
,        LPAD(FORMAT(SUM(
           CASE
             WHEN EXTRACT(MONTH FROM transaction_date) = 3 THEN transaction_amount
             ELSE 0
           END),2),8,' ') AS "Mar"
,        LPAD(FORMAT(SUM(
           CASE
             WHEN EXTRACT(MONTH FROM transaction_date) IN (1,2,3) THEN transaction_amount
             ELSE 0
           END),2),8,' ') AS "1FQ"
FROM     transaction
WHERE    transaction_date BETWEEN '2020-01-15' AND '2021-03-15'
GROUP BY EXTRACT(YEAR FROM transaction_date)
ORDER BY 1;

It returns:

+------+-----------+----------+----------+----------+
| Year | Jan       | Feb      | Mar      | 1FQ      |
+------+-----------+----------+----------+----------+
| 2020 | $    0.00 |    22.02 |    32.06 |    54.08 |
| 2021 | $   56.25 |    23.02 |     0.00 |    79.27 |
+------+-----------+----------+----------+----------+
2 rows in set (0.01 sec)

As always, I hope this helps answer a question that somebody is trying to sort out.

Written by maclochlainn

June 23rd, 2021 at 12:23 pm

Posted in MySQL,MySQL 8,MySQL Client,MySQL Workbench

Tagged with MySQL DBA, MySQL Developer

MySQL Outer Joins

without comments

The students needed yet another example of LEFT JOIN, RIGHT JOIN, and FULL JOIN syntax (by combining a left and right join with the UNION set operator). To that end, I put this set of examples together.

The example also shows how to order the result set from a derived table with the UNION operator. It uses the WITH clause to build a Common Table Expression (CTE), which allows the query to order the UNION set operator’s product based on the left and right join queries. It uses a CASE statement to order the result sets. The left_table is the parent table and the right_table is the child table in the relationship, which means the right_table holds a left_id foreign key column that lets you connect matching rows in the left_table.

You build the little model with the following script:

-- -----------------------------------------------------------------
-- Drop the demonstration tables.
-- -----------------------------------------------------------------
DROP TABLE IF EXISTS left_table, right_table;
 
-- -----------------------------------------------------------------
-- Create left_table.
-- -----------------------------------------------------------------
CREATE TABLE left_table
( left_id        int unsigned primary key auto_increment
, leftstring     varchar(10));
 
-- -----------------------------------------------------------------
-- Create left_table.
-- -----------------------------------------------------------------
CREATE TABLE right_table
( right_id       int unsigned primary key auto_increment
, left_id        int unsigned
, rightstring         varchar(10));
 
-- -----------------------------------------------------------------
-- Insert five rows to the left table, which holds a 
-- left_id primary key column.
-- -----------------------------------------------------------------
INSERT INTO left_table (leftstring) values ('One');
INSERT INTO left_table (leftstring) values ('Two');
INSERT INTO left_table (leftstring) values ('Three');
INSERT INTO left_table (leftstring) values ('Four');
INSERT INTO left_table (leftstring) values ('Five');
 
-- -----------------------------------------------------------------
-- Delete row four to create a gap.
-- -----------------------------------------------------------------
DELETE FROM left_table where left_id = 4;
 
-- -----------------------------------------------------------------
--  Insert four rows, skipping a foreign key value for the 
--  left_id primary key value of 2.
-- -----------------------------------------------------------------
 
INSERT INTO right_table (rightstring,left_id) values ('One',1);
INSERT INTO right_table (rightstring,left_id) values ('Three',3);
INSERT INTO right_table (rightstring,left_id) values ('Four',4);
INSERT INTO right_table (rightstring,left_id) values ('Five',5);

-- ----------------------------------------------------------------- -- Drop the demonstration tables. -- ----------------------------------------------------------------- DROP TABLE IF EXISTS left_table, right_table; -- ----------------------------------------------------------------- -- Create left_table. -- ----------------------------------------------------------------- CREATE TABLE left_table ( left_id int unsigned primary key auto_increment , leftstring varchar(10)); -- ----------------------------------------------------------------- -- Create left_table. -- ----------------------------------------------------------------- CREATE TABLE right_table ( right_id int unsigned primary key auto_increment , left_id int unsigned , rightstring varchar(10)); -- ----------------------------------------------------------------- -- Insert five rows to the left table, which holds a -- left_id primary key column. -- ----------------------------------------------------------------- INSERT INTO left_table (leftstring) values ('One'); INSERT INTO left_table (leftstring) values ('Two'); INSERT INTO left_table (leftstring) values ('Three'); INSERT INTO left_table (leftstring) values ('Four'); INSERT INTO left_table (leftstring) values ('Five'); -- ----------------------------------------------------------------- -- Delete row four to create a gap. -- ----------------------------------------------------------------- DELETE FROM left_table where left_id = 4; -- ----------------------------------------------------------------- -- Insert four rows, skipping a foreign key value for the -- left_id primary key value of 2. -- ----------------------------------------------------------------- INSERT INTO right_table (rightstring,left_id) values ('One',1); INSERT INTO right_table (rightstring,left_id) values ('Three',3); INSERT INTO right_table (rightstring,left_id) values ('Four',4); INSERT INTO right_table (rightstring,left_id) values ('Five',5);

Here are the join statements:

INNER JOIN

The INNER JOIN only returns those rows that match between a primary and foreign key column or set of columns.

SELECT l.left_id
,      l.leftstring
,      r.left_id
,      r.right_id
,      r.rightstring
FROM   left_table l INNER JOIN right_table r
ON     l.left_id = r.left_id;