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mysql

Run MySQL in a Docker container

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How to run MySQL commands in a Docker container.

#!/bin/bash
set -a; source <(cat .env | sed -e '/^#/d;/^\s*$/d' -e "s/'/'\\\''/g" -e "s/=\(.*\)/='\1'/g"); set +a
docker exec wp_db mysql -uroot -p${MYSQL_PASSWORD} -e " \
use db1; \
select * from wp_options where option_name='siteurl'; \
select * from wp_options where option_name='home';" 2>/dev/null
  • The first command loads the content of .env to environment variables.
  • The MySQL password can then be used using the ${MYSQL_PASSWORD} variable.
  • I’m using sed to get around the special characters in the password.
  • The second command runs docker exec on wp_db container.
  • The last 3 commands are the actual sql commands.
  • We are selecting to use the db1 database.
  • Then we run select statements from the wp_options table.
  • Finally, 2>/dev/null suppresses errors and warning to null.

Database Clients on Linux

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You can run database clients on your Linux distro by installing them.

MySQL

$ yum install mysql
$ apt install mysql

Postgress

$ yum install postgresql postgresql-client
$ apt install postgresql postgresql-client

MSSQL

$ yum install mysql-tools
$ apt install mssql-tools

MySQL Select Like

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Here’s how to perform SQL searches using the like operator.

# Format
SELECT column1, column2 FROM table_name WHERE column LIKE pattern;
# Search for an entry starting with a 'joe.'
SELECT id,username,address FROM users WHERE username LIKE 'joe%';
# Search for an entry ending with a 'joe.' 
SELECT id,username,address FROM users WHERE username LIKE '%joe';
# Search for any entry with 'joe' from any position. 
SELECT id,username,address FROM users WHERE username LIKE '%joe%';
# Finally, using "_" as wildcards. Find any field with "j" in the second position.
SELECT id,username,address FROM users WHERE username LIKE '_j';

MySQL Read Only

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If you need to perform backup or replicate a database, you can lock up the database by doing a global read block to make it read-only.

The process is:

  1. Make the server read-only, so that it processes only retrievals and blocks updates.
  2. You can then perform the backup.
  3. Change the server back to its normal read/write state.

Read only.

FLUSH TABLES WITH READ LOCK;
SET GLOBAL read_only = ON;

Back to normal mode.

SET GLOBAL read_only = OFF;
UNLOCK TABLES;

You can run these MySQL commands within MySQL or via a bash terminal. Check out my previous post.

Running MySQL commands from the Terminal

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You can run MySQL commands from the terminal by using -e switch. Here are a few examples.

mysql -u username -p -e "create database mydb"
mysql -u username -p -e "use mydb"
mysql -u username -p database -e "select * from mytable"

If you have .mycnf configured, you can omit the username and password.

mysql -e "create database mydb"
mysql -e "use mydb"
mysql -e "select * from mytable"

To run multiple commands from a single line, separate the commands using a semicolon.

mysql -e "create database somedb; use mydb; select * from mytable;"

Change MySQL User Password

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This is a very simple command to run. Login to MySQL first and run the following the command line.

ALTER USER username IDENTIFIED BY 'password';

Flush privileges for changes to take effect.

flush privileges;

WordPress Read Only

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Here’s how to create a WordPress site that’s read only. You will not be able to create, update and delete posts.

  1. Login to MySQL or MariaDB.
  2. Choose mysql database.
  3. Create a new user called ‘wpro’ for WordPress read only.
  4. Grant select permissions to all tables in ‘wordpress’ database.
  5. Flush privileges to commit your changes.
mariadb -u root -p
use mysql;
create user 'wpro'@'localhost' identified by 'yourpassword';
grant select on wordpress.* to 'wpro'@'localhost';
flush privileges;

In MySQL or MariaDB, you have to terminate all commands with a semicolon.

Now edit your WordPress wp-config.php file. vim /var/www/wordpress/wp-config.php.

/** MySQL database username */
define('DB_USER', 'wpro');
 
/** MySQL database password */
define('DB_PASSWORD', 'yourpassword');

After saving the wp-config.php file, everything should work just like before, except that you will not be able to save, publish or delete posts, pages, or add or delete media files to your WordPress site. It’s working as intended.

MySQL Read Only

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Here’s how to make a MySQL database read only.

mysql> FLUSH TABLES WITH READ LOCK;
mysql> SET GLOBAL read_only = ON;

It’s very useful if creating a replica database.