Archive for the ‘MySQL Client’ Category
MySQL+Credentials
The first tutorial supplementing the MySQL Connector/NET Developer Guide showed you how to connect and run static INSERT statement. It was a barebones PowerShell script with the MySQL Connector. This post shows you how to run a PowerShell script that uses a dynamic form to gather the MySQL credentials and then run a static query. Below is the MySQL Credentials form.
You enter the correct user name, password, hostname (or IP address), port, and database, like this:
Here’s the complete code for this staticQuery.ps1 PowerShell script:
# Add libraries for form components. Add-Type -AssemblyName System.Windows.Forms Add-Type -AssemblyName System.Drawing # Define a user credential form. $form = New-Object System.Windows.Forms.Form $form.Text = 'User Credential Form' $form.Size = New-Object System.Drawing.Size(300,240) $form.StartPosition = 'CenterScreen' # Define a button and assign it and its controls to a form. $loginButton = New-Object System.Windows.Forms.Button $loginButton.Location = New-Object System.Drawing.Point(60,160) $loginButton.Size = New-Object System.Drawing.Size(75,23) $loginButton.Text = 'Login' $loginButton.DialogResult = [System.Windows.Forms.DialogResult]::OK $form.AcceptButton = $loginButton $form.Controls.Add($loginButton) # Define a button and assign it and its controls to a form. $cancelButton = New-Object System.Windows.Forms.Button $cancelButton.Location = New-Object System.Drawing.Point(155,160) $cancelButton.Size = New-Object System.Drawing.Size(75,23) $cancelButton.Text = 'Cancel' $cancelButton.DialogResult = [System.Windows.Forms.DialogResult]::Cancel $form.CancelButton = $cancelButton $form.Controls.Add($cancelButton) # Define a label and assign it and its controls to a form. $userLabel = New-Object System.Windows.Forms.Label $userLabel.Location = New-Object System.Drawing.Point(30,15) $userLabel.Size = New-Object System.Drawing.Size(100,20) $userLabel.Text = 'Enter User Name:' $form.Controls.Add($userLabel) # Define a TextBox and assign it and its controls to a form. $userTextBox = New-Object System.Windows.Forms.TextBox $userTextBox.Location = New-Object System.Drawing.Point(140,15) $userTextBox.Size = New-Object System.Drawing.Size(100,20) $form.Controls.Add($userTextBox) # Define a label and assign it and its controls to a form. $pwdLabel = New-Object System.Windows.Forms.Label $pwdLabel.Location = New-Object System.Drawing.Point(30,40) $pwdLabel.Size = New-Object System.Drawing.Size(100,20) $pwdLabel.Text = 'Enter Password:' $form.Controls.Add($pwdLabel) # Define a TextBox and assign it and its controls to a form. $pwdTextBox = New-Object System.Windows.Forms.TextBox $pwdTextBox.Location = New-Object System.Drawing.Point(140,40) $pwdTextBox.Size = New-Object System.Drawing.Size(100,20) $pwdTextBox.PasswordChar = "*" $form.Controls.Add($pwdTextBox) # Define a label and assign it and its controls to a form. $hostLabel = New-Object System.Windows.Forms.Label $hostLabel.Location = New-Object System.Drawing.Point(30,65) $hostLabel.Size = New-Object System.Drawing.Size(100,20) $hostLabel.Text = 'Enter Hostname:' $form.Controls.Add($hostLabel) # Define a TextBox and assign it and its controls to a form. $hostTextBox = New-Object System.Windows.Forms.TextBox $hostTextBox.Location = New-Object System.Drawing.Point(140,65) $hostTextBox.Size = New-Object System.Drawing.Size(100,20) $form.Controls.Add($hostTextBox) # Define a label and assign it and its controls to a form. $portLabel = New-Object System.Windows.Forms.Label $portLabel.Location = New-Object System.Drawing.Point(30,90) $portLabel.Size = New-Object System.Drawing.Size(100,20) $portLabel.Text = 'Enter Port #:' $form.Controls.Add($portLabel) # Define a TextBox and assign it and its controls to a form. $portTextBox = New-Object System.Windows.Forms.TextBox $portTextBox.Location = New-Object System.Drawing.Point(140,90) $portTextBox.Size = New-Object System.Drawing.Size(100,20) $form.Controls.Add($portTextBox) # Define a label and assign it and its controls to a form. $dbLabel = New-Object System.Windows.Forms.Label $dbLabel.Location = New-Object System.Drawing.Point(30,115) $dbLabel.Size = New-Object System.Drawing.Size(100,20) $dbLabel.Text = 'Enter DB Name:' $form.Controls.Add($dbLabel) # Define a TextBox and assign it and its controls to a form. $dbTextBox = New-Object System.Windows.Forms.TextBox $dbTextBox.Location = New-Object System.Drawing.Point(140,115) $dbTextBox.Size = New-Object System.Drawing.Size(100,20) $form.Controls.Add($dbTextBox) $form.Topmost = $true $form.Add_Shown({$userTextBox.Select()}) $result = $form.ShowDialog() if ($result -eq [System.Windows.Forms.DialogResult]::OK) { # Assign inputs to connection variables. $uid = $userTextBox.Text $pwd = $pwdTextBox.Text $server = $hostTextBox.Text $port= $portTextBox.Text $dbName = $dbTextBox.Text # Declare connection string. $credentials = 'server=' + $server + ';port=' + $port + ';uid=' + $uid + ';pwd=' + $pwd + ';database=' + $dbName # Connect to the libaray MySQL.Data.dll Add-Type -Path 'C:\Program Files (x86)\MySQL\Connector NET 8.0\Assemblies\v4.5.2\MySql.Data.dll' # Create a MySQL Database connection variable that qualifies: # [Driver]@ConnectionString # ============================================================ # You can assign the connection string before using it or # while using it, which is what we do below by assigning # literal values for the following names: # - server=<ip_address> or 127.0.0.1 for localhost # - port=<port #> # - uid=<user_name> # - pwd=<password> # - database=<database_name> # ============================================================ $Connection = [MySql.Data.MySqlClient.MySqlConnection]@{ConnectionString=$credentials} $Connection.Open() # Define a MySQL Command Object for a non-query. $sqlCommand = New-Object MySql.Data.MySqlClient.MySqlCommand $sqlDataAdapter = New-Object MySql.Data.MySqlClient.MySqlDataAdapter $sqlDataSet = New-Object System.Data.DataSet # Assign the connection and command text to the MySQL command object. $sqlCommand.Connection = $Connection $sqlCommand.CommandText = 'SELECT CONCAT(first_name," ",last_name) AS full_name ' + ', avenger ' + 'FROM avenger' # Assign the connection and command text to the query method of # the data adapter object. $sqlDataAdapter.SelectCommand=$sqlCommand # Assign the tuples of data to a data set and return the number of rows fetched. $rowsFetched=$sqlDataAdapter.Fill($sqlDataSet, "data") # Print to console the data returned from the query. foreach($row in $sqlDataSet.tables[0]) { write-host "Avenger:" $row.avenger "is" $row.full_name } # Close the MySQL connection. $Connection.Close() } |
I created an avenger table and populated it with six rows of data:
-- Create the avenger table. CREATE TABLE db_connect ( db_connect_id INT UNSIGNED PRIMARY KEY AUTO_INCREMENT , version VARCHAR(10) , user VARCHAR(24) , db_name VARCHAR(10)); -- Seed the avenger table with data. INSERT INTO avenger ( first_name, last_name, avenger ) VALUES ('Anthony', 'Stark', 'Iron Man') ,('Thor', 'Odinson', 'God of Thunder') ,('Steven', 'Rogers', 'Captain America') ,('Bruce', 'Banner', 'Hulk') ,('Clinton', 'Barton', 'Hawkeye') ,('Natasha', 'Romanoff', 'Black Widow'); |
You run the staticQuery.ps1 PowerShell script from the Windows command shell with the following syntax:
powershell .\staticQuery.ps1 |
After running the staticQuery.ps1 PowerShell script, it writes the following to the local console but with minimal effort you can redirect it to a file:
Avenger: Iron Man is Anthony Stark Avenger: God of Thunder is Thor Odinson Avenger: Captain America is Steven Rogers Avenger: Hulk is Bruce Banner Avenger: Hawkeye is Clinton Barton Avenger: Black Widow is Natasha Romanoff |
As always, I hope this helps those looking to use this technology. My guess is the principal uses will be DevOps and Data Engineers.
MySQL Script Test
There are many ways to test and edit files. A lot of developers only use their favorite Integrated Developer Environment (IDE) but I find testing script files within the scope of a pipelined set of scripts much faster.
The ability to edit a script from within the MySQL Command-Line Interface (CLI) or MySQL Shell would be nice but unfortunately, doesn’t exist. You can always subshell to edit a file or list files in the present working directory, like:
mysql> \! vi task.sql |
I prefer to test at the OS level while leveraging the up-arrow key for command history. Here’s my quick edit and test script technique from your present working directory:
- Assume you create a
task.sqltest file, like:SELECT user() AS "Current User"\G
- You can edit with
vioremacand test the script interactively from the present working directory.- You can edit the file with the following syntax:
vi task.sql -
then, you can test the
task.sqlfile:mysql -ustudent -p -Dstudentdb < task.sql
- It returns the following:
Enter password: *************************** 1. row *************************** Current User: student@localhost
- If you have the desired outcome, you’re done. However, if you need further change you repeat the process.
- You can edit the file with the following syntax:
As always, I hope this helps those looking for a quick way to accomplish a task.
MySQL Transaction Scope
The idea of ACID transactions are a basic feature of SQL’s individual Data Manipulation Language (DML) commands, like the INSERT, UPDATE, and DELETE statements. Transactions across two or more tables are a natural extension of ACID compliance features provided by DML commands. However, they require a structured programming approach, like a store procedure or like API implemented in an imperative language.
Surprisingly, transaction management wasn’t covered well in Alan Beaulieu’s Learning SQL because he only provided pseudo code logic. While I thought troubleshoot some broken MySQL SQL/PSM logic would be a good learning experience for students, it wasn’t. So, I wrote this sample code to show how to achieve an all or nothing transaction across four tables.
The code for this example on transaction management lets you perform the important tasks necessary to effect transaction management:
- You must disable autocommit in the scope of the session.
- You must use an imperative programming language like SQL/PSM or Python, et cetera.
- You must identify an error thrown in a series of DML transactions, rollback all completed work, and exit the scope of the program unit.
This SQL defines the four tables:
/* Drop and create four tables. */ DROP TABLE IF EXISTS one, two, three, four; CREATE TABLE one ( id int primary key auto_increment, msg varchar(10)); CREATE TABLE two ( id int primary key auto_increment, msg varchar(10)); CREATE TABLE three ( id int primary key auto_increment, msg varchar(10)); CREATE TABLE four ( id int primary key auto_increment, msg varchar(10)); |
Unfortunately, there’s no way to simply transaction management from the MySQL Command-Line Interface (CLI) because you need to build the logic that manages success and failure. It requires that you create a procedure using MySQL’s SQL/PSM (Persistent Stored Module) or another imperative programming language. You might think why can’t you just write an anonymous block program, like you can do in other stored procedural languages. The answer is simple. You can’t write anonymous blocks in MySQL’s SQL/PSM because they adhere to ANSI SQL-2003 (or more accurately ISO/IEC 9075-4:2003).
The following code block does:
- Conditionally drops the locking() procedure.
- Sets the default semicolon (
;) delimiter to a double-dollar ($$), which lets you use the semicolon as statement and block terminators. - Declares a
locking()procedure with the following:- Sets a parameter list with four IN-mode parameters.
- Declares an
EXIThandler that undoes any writes before an error in a sequence of DDL commands, like theINSERT,UPDATE, orDELETEstatements. TheEXIThandler then aborts completion of the rest of the procedure. (MySQL 13.6.7.2 Declare … Handler Statement) - Disables autocommit in the scope of the session.
- Starts a transaction context and inserts data into four tables as a transaction. The continue handler picks up processing when one of the
INSERTstatements fails with a 1406 error code. The 1406 error code represents an error that occurs because the data is too long for a column’s width. - When all elements of the procedure complete, you commit the work.
/* Conditionally drop procedure. */ DROP PROCEDURE IF EXISTS locking; /* Set delimiter to $$ to allow ; inside the procedure. */ DELIMITER $$ /* Create a transaction procedure. */ CREATE PROCEDURE locking(IN pv_one varchar(10) ,IN pv_two varchar(10) ,IN pv_three varchar(10) ,IN pv_four varchar(10)) BEGIN /* Declare an EXIT Handler when a string is too long for a column. Undo all prior writes with a ROLLBACK statement. */ DECLARE EXIT HANDLER FOR 1406 BEGIN ROLLBACK; END; /* Disable autocommit. */ SET AUTOCOMMIT=0; /* Start transaction scope. */ START TRANSACTION; /* A series of INSERT statement. */ INSERT INTO one (msg) VALUES (pv_one); INSERT INTO two (msg) VALUES (pv_two); INSERT INTO three (msg) VALUES (pv_three); INSERT INTO four (msg) VALUES (pv_four); /* Commit transaction set. */ COMMIT; END; $$ /* Reset delimiter to ; for SQL statements. */ DELIMITER ; |
The next block tests the locking() procedure. The first and third calls are successful but the second one fails because the third parameter is too long for the msg column in the three table. The error triggers the EXIT handler in the locking() procedure.
/* Call locking procedure. */ CALL locking('Donald','Goofy','Mickey','Pluto'); CALL locking('Squirrel','Chipmunk','Monkey business','Raccoon'); CALL locking('Curly','Larry','Moe','Shemp'); |
The query block below:
/* Select from tables, which should be empty. */ SELECT * FROM one; SELECT * FROM two; SELECT * FROM three; SELECT * FROM four; |
Returns the following, which shows only the first and third test cases succeed:
+----+--------+ | id | msg | +----+--------+ | 1 | Donald | | 2 | Curly | +----+--------+ 2 rows in set (0.01 sec) +----+-------+ | id | msg | +----+-------+ | 1 | Goofy | | 2 | Larry | +----+-------+ 2 rows in set (0.00 sec) +----+--------+ | id | msg | +----+--------+ | 1 | Mickey | | 2 | Moe | +----+--------+ 2 rows in set (0.00 sec) +----+-------+ | id | msg | +----+-------+ | 1 | Pluto | | 2 | Shemp | +----+-------+ 2 rows in set (0.00 sec) |
As always, I hope this helps those trying to write transactions across multiple tables.
MySQL macOS Docker
While you can download MySQL as a DMG package, a number of users would prefer to install it as a Docker instance. You won’t find the macOS downloads on the same web site as other downloads. You can use the following macOS download site.
After installing Docker on your macOS, you can pull a copy of the current MySQL Server with the following command:
docker pull mysql/mysql-server |
You should create a mysql directory inside your ~/Documents directory with this command:
mkdir ~/Documents/mysql |
Then, you should use the cd command to change into the ~/Documents/mysql directory and run this command:
pwd |
It should return the following directory:
/Users/<user_name>/Documents/mysql |
Use the /Users/<user_name>/Documents/mysql as the
docker run --name=mysql1 --volume=<path_to_folder>:/var/lib/mysql -p 33060:3306/tcp -d mysql/mysql-server |
The --name option value is mysql1 and it becomes the container value. Docker mounts the column in the ~/Documents/mysql folder. All data from the Docker container under the /var/lib/mysql directory will persist in this directory. This directory will still contain the database when the container is shut down.
The docker run command maps the localhost’s 33060 port to the 3306 port on the Docker container. You will use the 33060 port to connect to the Docker instance of MySQL. It raises a dialog box asking for permission to access the directory. You need to allow Docker to write to the ~/Documents/mysql directory.
You can verify that the Docker container is running with the following command:
docker ps |
It should return:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 142b5c491cd8 mysql/mysql-server "/entrypoint.sh mysq…" 7 minutes ago Up 6 minutes (healthy) 33060-33061/tcp, 0.0.0.0:33060->3306/tcp mysql1 |
You can get the MySQL generated root password with this Docker command:
docker logs mysql1 2>&1 | grep GENERATED |
It returns something like the following:
[Entrypoint] GENERATED ROOT PASSWORD: vop#3GNYqK3nC@S@N3haf3nox5E |
Use the following Docker command to connect to the Docker container:
docker exec -it mysql1 /bin/bash |
It launches a Bash shell inside the Docker container:
bash-4.2# |
Start the mysql Command-Line Interface (CLI):
mysql -uroot -p |
You are then prompted for a password:
Enter password: |
After successfully entering the password, you’ll see the following:
Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 55 Server version: 8.0.22 Copyright (c) 2000, 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 '\h' for help. Type '\c' to clear the current input statement. mysql> |
Unless you want to remember that hugely complex root password, you should consider changing it to something simple like, 'cangetin' with the following command:
ALTER USER 'root'@'localhost' IDENTIFIED WITH MYSQL_NATIVE_PASSWORD BY 'cangetin'; |
Next, you should check for the installed databases with this command:
show databases; |
It will return:
+--------------------+ | Database | +--------------------+ | information_schema | | mysql | | performance_schema | | sys | +--------------------+ 4 rows in set (0.01 sec) |
Exiting mysql, you can see the contents of the root user’s directory with this list command:
ls -al |
It should return:
total 84 drwxr-xr-x 1 root root 4096 Jan 12 03:41 . drwxr-xr-x 1 root root 4096 Jan 12 03:41 .. -rwxr-xr-x 1 root root 0 Jan 12 03:41 .dockerenv lrwxrwxrwx 1 root root 7 Oct 12 22:06 bin -> usr/bin dr-xr-xr-x 2 root root 4096 Apr 11 2018 boot drwxr-xr-x 5 root root 340 Jan 12 03:41 dev drwxr-xr-x 2 root root 4096 Oct 19 05:47 docker-entrypoint-initdb.d -rwxr-xr-x 1 root root 7496 Oct 19 05:37 entrypoint.sh drwxr-xr-x 1 root root 4096 Jan 12 03:41 etc -rw-r--r-- 1 root root 86 Jan 12 03:41 healthcheck.cnf -rwxr-xr-x 1 root root 1073 Oct 19 05:37 healthcheck.sh drwxr-xr-x 2 root root 4096 Apr 11 2018 home lrwxrwxrwx 1 root root 7 Oct 12 22:06 lib -> usr/lib lrwxrwxrwx 1 root root 9 Oct 12 22:06 lib64 -> usr/lib64 drwxr-xr-x 2 root root 4096 Apr 11 2018 media drwxr-xr-x 2 root root 4096 Apr 11 2018 mnt -rw-r--r-- 1 root root 0 Jan 12 03:41 mysql-init-complete drwxr-xr-x 2 root root 4096 Apr 11 2018 opt dr-xr-xr-x 127 root root 0 Jan 12 03:41 proc dr-xr-x--- 1 root root 4096 Jan 12 04:21 root drwxr-xr-x 1 root root 4096 Oct 19 05:47 run lrwxrwxrwx 1 root root 8 Oct 12 22:06 sbin -> usr/sbin drwxr-xr-x 2 root root 4096 Apr 11 2018 srv dr-xr-xr-x 13 root root 0 Jan 12 03:41 sys drwxrwxrwt 1 root root 4096 Jan 12 03:41 tmp drwxr-xr-x 1 root root 4096 Oct 12 22:06 usr drwxr-xr-x 1 root root 4096 Oct 12 22:06 var |
At this point, you have to make a choice about how you will access the MySQL database. You have a couple options:
- Create an individual
studentuser that can access the MySQL-Server as a micro-service, which would only be a MySQL user connecting through MySQL workbench. At least, that’s the only connection option unless you likewise install themysqlclient on your host macOS. Themysqlclient lets you connect from the host operating system through the Command-Line Interface (CLI). - Create a local
studentuser account inside the Docker container. It will have access to the container file system and mimic the behavior of a non-rootuser on a server.
Let’s create both for this demonstration. Reconnect as the root user and issue the following two commands:
CREATE USER 'student'@'localhost' IDENTIFIED WITH MYSQL_NATIVE_PASSWORD BY 'student'; CREATE USER 'student'@'%.%.%.%' IDENTIFIED WITH MYSQL_NATIVE_PASSWORD BY 'student'; |
The first version of the student user lets you access the database from inside the Docker container. The second version of the student user lets you access the database from MySQL Workbench deployed on your base macOS.
You can add a sakila database and grant all privileges to the student user with the following command as the root user:
CREATE DATABASE sakila; GRANT ALL ON sakila.* TO 'student'@'localhost'; GRANT ALL ON sakila.* TO 'student'@'%.%.%.%'; |
You need to get the sakila database from the Internet within the Docker container. Exit the mysql client with the following command:
quit; |
As the root user, install the wget and tar Linux utilities with this command:
yum install -y wget tar |
As the student user, you can use the wget command to grab a copy of the sakila database and store the database locally. Use the cd command to get to your ${HOME} directory, like:
cd |
Use this syntax to get a copy of the sakila database:
wget http://downloads.mysql.com/docs/sakila-db.tar.gz |
Use the ls command to verify the download, then run the following set of Linux commands from the Linux CLI:
tar -xzf sakila-db.tar.gz cd sakila-db |
Run the following two commands from the sakila-db directory:
mysql -ustudent -p < sakila-schema.sql mysql -ustudent -p < sakila-data.sql |
or, you can connect as the student user to the MySQL client and run them there:
source sakila-schema.sql source sakila-data.sql |
You create a non-root student user for the Docker container from the macOS host opearting system. Which means you need to quit; the mysql client, and exit the root user’s session with the Docker container.
At the terminal in your macOS, issue the following Docker command to create a student account in the mysql1 container:
docker exec mysql1 bash -c "useradd -u 501 -g mysql -G users \ > -d /home/student -s /bin/bash -c "Student" -n student" |
Now, you can connect as the student user to the mysql1 container, with the following Docker command:
docker exec -it --user student mysql1 bash |
The first time you connect, you will be a the / (root) directory. Use the following cd command to go to the student user’s home directory:
cd |
Then, type the following command to set the student user’s home directory as the default. You need to use this command because vim isn’t installed in the default Docker container, which would let you interactively edit files. It appends the necessary Bash shell command to the end of the .bashrc file.
echo 'cd ${HOME}' >> .bashrc |
With this change, the student user will always be available form its home directory next time you connect to the mysql1 container. You can use scp to move files into the student user’s home (/home/student) directory. However, you can create a quick test.sql file like this:
echo "select user();" > test.sql |
Connect to the mysql CLI with as the student user:
mysql -ustudent -p |
Call your test.sql file from the Linux CLI, like:
mysql -ustudent -p < test.sql |
or, you can run the test.sql program as follows form the MySQL command-line:
source test.sql |
It will return:
+-------------------+ | user() | +-------------------+ | student@localhost | +-------------------+ 1 row in set (0.00 sec) |
That’s the basic setup of the Docker MySQL Container on the macOS. You can do much more once you’ve configured it like this. For example, you can add vim to your library repository as the root user with the following command:
yum install -y vim |
It just takes a minute or a bit more. Adding vim opens up so much flexibility for you inside the Docker container, it’s impossible for me to resist. 😉
MySQL sakila Database
While I thought my instructions were clear, it appears there should have been more in my examples for using the MySQL MSI. A key thing that happened is that students opted not to install:
Samples and Examples 8.0.22 |
Unfortunately, they may not have read the Preface of Alan Beaulieu’s Learning SQL, 3rd Edition where he explains how to manually download the files from the MySQL web site. Here are those, very clear, instructions (pg. XV) with my additions in italics for the MySQL Shell:
First, you will need to launch the mysql command-line client or the mysqlsh command-line shell, and provide a password, and then perform the following steps:
- Go to https://dev.mysql.com/doc/index-other.html and download the files for the “
sakiladatabase” under the Example Database section. - Put the files in the local directory such as
C:\temp\sakila-db(used for the next two steps, but overwrite with your directory path). - Type
source c:\temp\sakila-db\sakila-schema.sql
and press enter.
- Type
source c:\temp\sakila-db\sakila-data.sql
and press enter.
These instructions let you create the sakila database without rerunning the MSI to add a product. Naturally, you can avoid these steps by using the GUI approach provided in the MySQL MSI file.
As always, I hope this helps those looking for how to solve problems.
MySQL Self-Join
I’m switching to MySQL and leveraging Alan Beaulieu’s Learning SQL as a supporting reference for my Database Design and Development course. While reviewing Alan’s Chapter 5: Querying Multiple Tables, I found his coverage of using self-joins minimal.
In fact, he adds a prequel_film_id column to the film table in the sakila database and then a single row to demonstrate a minimal self-join query. I wanted to show them how to view a series of rows interconnected by a self-join, like the following:
SELECT f.title AS film , fp.title AS prequel FROM film f LEFT JOIN film fp ON f.prequel_id = fp.film_id WHERE f.series_name = 'Harry Potter' ORDER BY f.series_number; |
It returns the following result set:
+----------------------------------------------+----------------------------------------------+ | film | prequel | +----------------------------------------------+----------------------------------------------+ | Harry Potter and the Chamber of Secrets | Harry Potter and the Sorcerer's Stone | | Harry Potter and the Prisoner of Azkaban | Harry Potter and the Chamber of Secrets | | Harry Potter and the Goblet of Fire | Harry Potter and the Prisoner of Azkaban | | Harry Potter and the Order of the Phoenix | Harry Potter and the Goblet of Fire | | Harry Potter and the Half Blood Prince | Harry Potter and the Order of the Phoenix | | Harry Potter and the Deathly Hallows: Part 1 | Harry Potter and the Half Blood Prince | | Harry Potter and the Deathly Hallows: Part 2 | Harry Potter and the Deathly Hallows: Part 1 | +----------------------------------------------+----------------------------------------------+ 7 rows in set (0.00 sec) |
Then, I thought about what questions the students might ask. For example, why doesn’t the query return the first film that doesn’t have a prequel. So, I took the self-join to the next level to display the first film having no prequel, like this:
SELECT f.title AS film , IFNULL( CASE WHEN NOT f.film_id = fp.film_id AND f.prequel_id = fp.film_id THEN fp.title END,'None') AS prequel FROM film f LEFT JOIN film fp ON f.prequel_id = fp.film_id WHERE f.series_name = 'Harry Potter' ORDER BY f.series_number; |
The CASE operator in the SELECT-list filters the result set by eliminating rows erroneously returned. Without the CASE filter, the query would return the original Harry Potter and the Sorcerer’s Stone film matched agains a NULL and all of the other sequels. The CASE operator effectively limits the result set for the LEFT JOIN to only the following data:
+----------------------------------------------+----------------------------------------------+ | film | prequel | +----------------------------------------------+----------------------------------------------+ | Harry Potter and the Sorcerer's Stone | NULL | +----------------------------------------------+----------------------------------------------+ |
The IFNULL() built-in function lets you replace the NULL value returned as the prequel’s title value. The IFNULL() function substitutes a 'None' string literal for a NULL value. The query returns the following result set:
+----------------------------------------------+----------------------------------------------+ | film | prequel | +----------------------------------------------+----------------------------------------------+ | Harry Potter and the Sorcerer's Stone | None | | Harry Potter and the Chamber of Secrets | Harry Potter and the Sorcerer's Stone | | Harry Potter and the Prisoner of Azkaban | Harry Potter and the Chamber of Secrets | | Harry Potter and the Goblet of Fire | Harry Potter and the Prisoner of Azkaban | | Harry Potter and the Order of the Phoenix | Harry Potter and the Goblet of Fire | | Harry Potter and the Half Blood Prince | Harry Potter and the Order of the Phoenix | | Harry Potter and the Deathly Hallows: Part 1 | Harry Potter and the Half Blood Prince | | Harry Potter and the Deathly Hallows: Part 2 | Harry Potter and the Deathly Hallows: Part 1 | +----------------------------------------------+----------------------------------------------+ 8 rows in set (0.01 sec) |
Alan’s modification of the sakila.film table had the following two related design flaws:
- It didn’t provide a way to guarantee the ordering of films with prequels because relational databases don’t guarantee ordered result sets unless you use an
ORDER BYclause, which typically requires a column to order. - It didn’t provide a way to isolate a series of films.
I modified the film table differently by adding the series_name, series_number, and prequel_id columns. The series_name column lets you group results and the series_number column lets you order by a preserved sequence that you store as part of the data The prequel_id column lets you connect to the prequel film, much like the backward portion of a doubly linked list.
The new sakila.film table is:
+----------------------+---------------------------------------------------------------------+------+-----+-------------------+-----------------------------------------------+ | Field | Type | Null | Key | Default | Extra | +----------------------+---------------------------------------------------------------------+------+-----+-------------------+-----------------------------------------------+ | film_id | smallint unsigned | NO | PRI | NULL | auto_increment | | title | varchar(255) | NO | MUL | NULL | | | description | text | YES | | NULL | | | release_year | year | YES | | NULL | | | language_id | tinyint unsigned | NO | MUL | NULL | | | original_language_id | tinyint unsigned | YES | MUL | NULL | | | rental_duration | tinyint unsigned | NO | | 3 | | | rental_rate | decimal(4,2) | NO | | 4.99 | | | length | smallint unsigned | YES | | NULL | | | replacement_cost | decimal(5,2) | NO | | 19.99 | | | rating | enum('G','PG','PG-13','R','NC-17') | YES | | G | | | special_features | set('Trailers','Commentaries','Deleted Scenes','Behind the Scenes') | YES | | NULL | | | last_update | timestamp | NO | | CURRENT_TIMESTAMP | DEFAULT_GENERATED on update CURRENT_TIMESTAMP | | series_name | varchar(20) | YES | | NULL | | | series_number | int unsigned | YES | | NULL | | | prequel | int unsigned | YES | | NULL | | +----------------------+---------------------------------------------------------------------+------+-----+-------------------+-----------------------------------------------+ 16 rows in set (0.21 sec) |
After adding the three new columns, I inserted eight rows for the original Harry Potter films. You can use the following script in the MySQL client (mysql) to add the columns and insert the data to test the preceding queries:
-- Use sakila database. USE sakila; -- Add a prequel_id column to the sakila.film table. ALTER TABLE film ADD (series_name varchar(20)), ADD (series_number int unsigned), ADD (prequel_id int unsigned); -- Set primary to foreign key local variable. SET @sv_film_id = 0; -- Insert Harry Potter films in sakila.film table with classic values clause. INSERT INTO film ( title , description , release_year , language_id , original_language_id , rental_duration , rental_rate , length , replacement_cost , rating , special_features , last_update , series_name , series_number , prequel_id ) VALUES ('Harry Potter and the Sorcerer''s Stone' ,'A film about a young boy who on his eleventh birthday discovers, he is the orphaned boy of two powerful wizards and has unique magical powers.' , 2001 , 1 , NULL , 3 , 0.99 , 152 , 19.99 ,'PG' ,'Trailers' ,'2001-11-04' ,'Harry Potter' , 1 , NULL ); -- Assign the last generated primary key value to the local variable. SET @sv_film_id := last_insert_id(); -- Insert 2nd film in sakila.film table with classic values clause. INSERT INTO film ( title , description , release_year , language_id , original_language_id , rental_duration , rental_rate , length , replacement_cost , rating , special_features , last_update , series_name , series_number , prequel_id ) VALUES ('Harry Potter and the Chamber of Secrets' ,'A film where Harry returning to Hogwarts, still famous and a hero, when strange things start to happen ... people are turning to stone and no-one knows what, or who, is doing it.' , 2002 , 1 , NULL , 3 , 0.99 , 160 , 19.99 ,'PG' ,'Trailers' ,'2002-11-15' ,'Harry Potter' , 2 , @sv_film_id ); -- Assign the last generated primary key value to the local variable. SET @sv_film_id := last_insert_id(); -- Insert 3rd film in sakila.film table with classic values clause. INSERT INTO film ( title , description , release_year , language_id , original_language_id , rental_duration , rental_rate , length , replacement_cost , rating , special_features , last_update , series_name , series_number , prequel_id ) VALUES ('Harry Potter and the Prisoner of Azkaban' ,'A film where Harry, Ron, and Hermione return for their third year at Hogwarts and are forced to face escaped prisoner, Sirius Black.' , 2004 , 1 , NULL , 3 , 0.99 , 141 , 19.99 ,'PG' ,'Trailers' ,'2004-06-04' ,'Harry Potter' , 3 , @sv_film_id ); -- Assign the last generated primary key value to the local variable. SET @sv_film_id := last_insert_id(); -- Insert 4th film in sakila.film table with classic values clause. INSERT INTO film ( title , description , release_year , language_id , original_language_id , rental_duration , rental_rate , length , replacement_cost , rating , special_features , last_update , series_name , series_number , prequel_id ) VALUES ('Harry Potter and the Goblet of Fire' ,'A film where where Harry Potter''s name emerges from the Goblet of Fire, and he becomes a competitor in a grueling battle for glory among three wizarding schools - the Triwizard Tournament.' , 2005 , 1 , NULL , 3 , 0.99 , 157 , 19.99 ,'PG' ,'Trailers' ,'2005-11-18' ,'Harry Potter' , 4 , @sv_film_id ); -- Assign the last generated primary key value to the local variable. SET @sv_film_id := last_insert_id(); -- Insert 5th film in sakila.film table with classic values clause. INSERT INTO film ( title , description , release_year , language_id , original_language_id , rental_duration , rental_rate , length , replacement_cost , rating , special_features , last_update , series_name , series_number , prequel_id ) VALUES ('Harry Potter and the Order of the Phoenix' ,'A film where Lord Voldemort has returned, but the Ministry of Magic is doing everything it can to keep the wizarding world from knowing the truth.' , 2007 , 1 , NULL , 3 , 0.99 , 138 , 19.99 ,'PG-13' ,'Trailers' ,'2007-07-12' ,'Harry Potter' , 5 , @sv_film_id ); -- Assign the last generated primary key value to the local variable. SET @sv_film_id := last_insert_id(); -- Insert 6th film in sakila.film table with classic values clause. INSERT INTO film ( title , description , release_year , language_id , original_language_id , rental_duration , rental_rate , length , replacement_cost , rating , special_features , last_update , series_name , series_number , prequel_id ) VALUES ('Harry Potter and the Half Blood Prince' ,'A film where Voldemort is tightening his grip on Hogwarts and it is no longer the safe haven it once was. Harry and Dumbledore work to find the key to unlock the Dark Lord''s defenses.' , 2009 , 1 , NULL , 3 , 0.99 , 153 , 19.99 ,'PG' ,'Trailers' ,'2009-07-15' ,'Harry Potter' , 6 , @sv_film_id ); -- Assign the last generated primary key value to the local variable. SET @sv_film_id := last_insert_id(); -- Insert 7th film in sakila.film table with classic values clause. INSERT INTO film ( title , description , release_year , language_id , original_language_id , rental_duration , rental_rate , length , replacement_cost , rating , special_features , last_update , series_name , series_number , prequel_id ) VALUES ('Harry Potter and the Deathly Hallows: Part 1' ,'A film where Harry, Ron and Hermione set out on their perilous mission to track down and destroy the Horcruxes - the keys to Voldemort''s immortality.' , 2010 , 1 , NULL , 3 , 0.99 , 146 , 19.99 ,'PG-13' ,'Trailers' ,'2010-11-19' ,'Harry Potter' , 7 , @sv_film_id ); -- Assign the last generated primary key value to the local variable. SET @sv_film_id := last_insert_id(); -- Insert 8th film in sakila.film table with classic values clause. INSERT INTO film ( title , description , release_year , language_id , original_language_id , rental_duration , rental_rate , length , replacement_cost , rating , special_features , last_update , series_name , series_number , prequel_id ) VALUES ('Harry Potter and the Deathly Hallows: Part 2' ,'A film where Harry, Ron and Hermione set out on their perilous mission to track down and destroy the Horcruxes - the keys to Voldemort''s immortality.' , 2011 , 1 , NULL , 3 , 0.99 , 130 , 19.99 ,'PG-13' ,'Trailers' ,'2011-07-15' ,'Harry Potter' , 8 , @sv_film_id ); |
You can put the following commands into a SQL script file to revert the sakila.film table to its base configuration:
DELETE FROM film WHERE film_id > 1000; ALTER TABLE film DROP COLUMN series_name; ALTER TABLE film DROP COLUMN series_number; ALTER TABLE film DROP COLUMN prequel_id; ALTER TABLE film AUTO_INCREMENT = 1000; |
As always, I hope this helps those looking for how to solve a new problem.
MySQL Client in 8.0.21+
Having recently installed a fresh copy of MySQL 8.0.21 on Windows, I took careful note of parsing changes in the MySQL Shell. It was tedious that we lost multiple statement processing, which is supported in the MySQL Client and MySQL Workbench because it uses MySQL Client.
It was frustrating when I subsequently discovered that the MySQL Shell took away the ability to write log files by removing the TEE and NOTEE commands. I suspected that since MySQL Workbench was still using the MySQL Client that it should be in the code tree. In fact, the mysql.exe client is in this directory:
C:\Program Files\MySQL\MySQL Server 8.0\bin |
So, I immediately created a batch file to put the MySQL Client into my %PATH% environment variable when needed. I used this time tested DOS command:
copy con mysqlclient.bat set PATH=%PATH%;C:\Program Files\MySQL\MySQL Server 8.0\bin;. ^Z |
Now you can call the MySQL client with the following syntax if you have a student user and studentdb database:
mysql -ustudent -p -Dstudentdb |
This way, I can just call it in a PowerShell utility before running migration script files that should generate log files for review. It also leaves the MySQL Client out of general use.
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