devkuma – MySQL

MySQL | Installing MySQL

kc@example.com (kc kim) — Mon, 07 Aug 2017 21:01:44 +0900

MySQL is currently available in two editions: MySQL Enterprise Edition and MySQL Community Server. MySQL Enterprise is the commercial edition and includes official support and administration tools. By contrast, MySQL Community Server is a free database. This article explains how to install MySQL Community Server with Docker.

Check the Docker Version

First, as expected, check whether Docker is installed.

docker --version

If the command prints a version as shown below, Docker is installed correctly.

 % docker --version
Docker version 20.10.8, build 3967b7d

Download the MySQL Docker Image

Run the following command to download the MySQL Docker image.

docker pull mysql

The output will look like this.

% docker pull mysql
Using default tag: latest
latest: Pulling from library/mysql
07aded7c29c6: Pull complete
f68b8cbd22de: Pull complete
30c1754a28c4: Pull complete
1b7cb4d6fe05: Pull complete
79a41dc56b9a: Pull complete
00a75e3842fb: Pull complete
b36a6919c217: Pull complete
635b0b84d686: Pull complete
6d24c7242d02: Pull complete
5be6c5edf16f: Pull complete
cb35eac1242c: Pull complete
a573d4e1c407: Pull complete
Digest: sha256:4fcf5df6c46c80db19675a5c067e737c1bc8b0e78e94e816a778ae2c6577213d
Status: Downloaded newer image for mysql:latest
docker.io/library/mysql:latest

If you run the command without specifying a version, Docker downloads the latest MySQL Docker image. To install a specific version, include the version as shown below.

docker pull mysql:{version}

Run a MySQL Docker Container

Run the following command to start the container.

docker run --name mysql -e MYSQL_ROOT_PASSWORD=1234 -d -p 3306:3306 mysql:latest

Here, the Docker container name is set to mysql with the --name option. You can use another name if you prefer.

% docker run --name mysql -e MYSQL_ROOT_PASSWORD=1234 -d -p 3306:3306 mysql:latest
79c4333a40db5621a9cb7051fac2a8702c09d0f2706223cf65a5c448b08cb061

Check That the MySQL Docker Container Is Running

Run the following command to check the container status.

docker ps

If it is running, you can see MySQL listed as shown below.

% docker ps
CONTAINER ID   IMAGE          COMMAND                  CREATED          STATUS          PORTS                                                  NAMES
79c4333a40db   mysql:latest   "docker-entrypoint.s..."   40 seconds ago   Up 39 seconds   0.0.0.0:3306->3306/tcp, :::3306->3306/tcp, 33060/tcp   mysql

Start, Stop, and Restart the MySQL Docker Container

Stop the MySQL Docker container.

$ docker stop mysql

Start the MySQL Docker container.

$ docker start mysql

Restart the MySQL Docker container.

$ docker restart mysql

Connect to the MySQL Docker Container

docker exec -it mysql bash

% docker exec -it mysql bash
root@79c4333a40db:/# mysql -u root -p
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 8.0.26 MySQL Community Server - GPL

Copyright (c) 2000, 2021, Oracle and/or its affiliates.

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> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
4 rows in set (0.01 sec)

mysql> ^C
mysql>

MySQL | Connecting to a Database from the Console

kc@example.com (kc kim) — Mon, 07 Aug 2017 21:01:44 +0900

This article explains how to connect to MySQL from a console or telnet environment.

Basic Connection Method

$ mysql -u {username} -p{password} {database_name}

Note: There is no space in -p{password}. If the password is 1234, enter -p1234.

Other Connection Methods

mysql -u {username} -p {database_name}
mysql -u root (when no account or password has been created)
mysql -u root -p (when the root password exists)

Run a Query Saved in an External File

Use the following command to run a query saved in an external file.

$ mysql -u {UserName} -p{Password} {Database} < {external_file_name}

This method is mainly used to import a file exported as SQL statements.

Example

First, create an external file at /Users/devkuma/test.sql.

SELECT * FROM store_information

Move to the directory where the mysql command is stored.

$ cd /usr/local/mysql/bin/

Run the external SQL file with the command.

$ ./mysql -u root -p1234 devkuma < /Users/devkuma/test.sql 
Warning: Using a password on the command line interface can be insecure.
region_name	store_name	sales	txn_date
West	Los Angeles	1500	1999-01-05
West	San Diego	250	1999-01-07
West	Los Angeles	300	1999-01-08
East	Boston	700	1999-01-08

View the Current Status

mysql> status

Example

mysql> status
--------------
./mysql  Ver 14.14 Distrib 5.6.17, for osx10.7 (x86_64) using  EditLine wrapper

Connection id:		1068
Current database:	
Current user:		root@localhost
SSL:			Not in use
Current pager:		stdout
Using outfile:		''
Using delimiter:	;
Server version:		5.6.17 MySQL Community Server (GPL)
Protocol version:	10
Connection:		Localhost via UNIX socket
Server characterset:	utf8
Db     characterset:	utf8
Client characterset:	utf8
Conn.  characterset:	utf8
UNIX socket:		/tmp/mysql.sock
Uptime:			1 hour 9 min 39 sec

Threads: 5  Questions: 4186  Slow queries: 0  Opens: 128  Flush tables: 1  Open tables: 107  Queries per second avg: 1.001
--------------

List Databases

mysql> show databases;

Example

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| devkuma            |
| mysampledata       |
| mysql              |
| performance_schema |
+--------------------+
5 rows in set (0.00 sec)

Select the Database to Use

mysql> use {database_name}

Example

mysql> use devkuma
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed

List Tables

mysql> show tables;

Example

mysql> show tables;
+----------------------------+
| Tables_in_devkuma          |
+----------------------------+
| geography                  |
| store_information          |
+----------------------------+
46 rows in set (0.00 sec)

Exit the Connection

mysql> exit
Bye

Or press Ctrl+C.

MySQL | Checking the Version

kc@example.com (kc kim) — Mon, 07 Aug 2017 21:01:44 +0900

There are two ways to check the MySQL version: with a command or with a query.

Checking with a Command

$ cd /usr/local/mysql/bin
$ ./mysql -V
./mysql  Ver 14.14 Distrib 5.6.17, for osx10.7 (x86_64) using  EditLine wrapper

Or:

$ ./mysql --version
./mysql  Ver 14.14 Distrib 5.6.17, for osx10.7 (x86_64) using  EditLine wrapper

Strictly speaking, the commands above check the version of the MySQL client, so they also display information about the installed client.

Checking with a Query

Connect to the server and run the following query.

mysql> SELECT VERSION();
+-----------+
| VERSION() |
+-----------+
| 5.6.17    |
+-----------+
1 row in set (0.00 sec)

Or:

mysql> SHOW VARIABLES LIKE '%VERSION%';
+-------------------------+------------------------------+
| Variable_name           | Value                        |
+-------------------------+------------------------------+
| innodb_version          | 5.6.17                       |
| protocol_version        | 10                           |
| slave_type_conversions  |                              |
| version                 | 5.6.17                       |
| version_comment         | MySQL Community Server (GPL) |
| version_compile_machine | x86_64                       |
| version_compile_os      | osx10.7                      |
+-------------------------+------------------------------+
7 rows in set (0.00 sec)

MySQL

kc@example.com (kc kim) — Mon, 07 Aug 2017 21:01:44 +0900

MySQL is one of the most widely used databases in the world and is currently developed by Oracle. This section introduces MySQL for readers who plan to use it. It explains, step by step, how to install MySQL in a local environment and how to use MySQL to create databases, tables, users, triggers, and related objects through simple hands-on examples.

MySQL | Create Tables and Add, Delete, or Modify Columns

kc@example.com (kc kim) — Mon, 07 Aug 2017 21:01:44 +0900

Create a Table

CREATE TABLE [table_name](id int, name varchar(20));

Rename a Table

RENAME TABLE [table_name] TO [new_table_name]

ALTER TABLE [table_name] RENAME [new_table_name];

Delete a Table

DROP TABLE [table_name];

Add a Column

ALTER TABLE [table_name] ADD [column_name] [type] [options];

ex) ALTER TABLE [table_name] ADD [column_name] varchar(100) not null default '0';

Delete a Column

alter TABLE [table_name] drop [column_name];

Rename a Column and Change Its Type

ALTER TABLE [table_name] change [column_name] [new_column_name] varchar(12);

Modify a Column Type

ALTER TABLE [table_name] MODIFY [column_name] varchar(14);

MySQL | Table Creation Error Related to DEFAULT timestamp

kc@example.com (kc kim) — Mon, 07 Aug 2017 21:01:44 +0900

In MySQL 5.5 and earlier, creating a table with a single TIMESTAMP field that uses a DEFAULT value, as shown below, is not a problem.

CREATE TABLE table_a (
  time_a timestamp DEFAULT CURRENT_TIMESTAMP
)

However, an error occurs when two TIMESTAMP columns are used.

CREATE TABLE table_a (
  time_a timestamp DEFAULT CURRENT_TIMESTAMP,
  time_b timestamp DEFAULT CURRENT_TIMESTAMP
)

The error message is as follows.

Error Code : 1293
Incorrect table definition; there can be only one TIMESTAMP column with CURRENT_TIMESTAMP in DEFAULT or ON UPDATE clause

This means that only one TIMESTAMP column in a table can specify CURRENT_TIMESTAMP as its DEFAULT value.

In this case, specify DEFAULT CURRENT_TIMESTAMP for only one field and initialize the other column with CURRENT_TIMESTAMP when inserting data.

CREATE TABLE table_a (
  time_a timestamp DEFAULT CURRENT_TIMESTAMP,
  time_b timestamp
)

This restriction was removed in MySQL 5.6, so upgrading from mysql-server-5.5 to mysql-server-5.6 resolves the issue.

If you are using Ubuntu Linux, you can upgrade with the following commands.

$ sudo apt-get update
$ sudo apt-get install mysql-server-5.6

Even if you already have databases managed by MySQL 5.5, installing 5.6 as shown above automatically migrates the databases, so you do not need to dump and move them separately. However, make a backup before installation in case something unexpected happens.

MySQL | Strings

kc@example.com (kc kim) — Mon, 07 Aug 2017 21:01:44 +0900

Concatenate Strings

You can concatenate strings or column values by using the concat function.

Function Format

concat(string_or_column_name, string_or_column_name, ...)

Example

SELECT concat("abc","123")

When you run the example above, the following result is displayed.

abc123

Cut a String from the Left

The left function cuts a string starting from the left.

Function Format

left(column_name_or_string, length_to_cut_from_the_left)

Example

SELECT left("abcdef", 3)

When you run the example above, the following result is displayed.

abc

Cut a String from the Right

The right function cuts a string starting from the right.

Function Format

right(column_name_or_string, length)

Example

SELECT right("abcdef", 3)

When you run the example above, the following result is displayed.

def

Cut a String from the Middle

The substring function cuts a string from the middle.

Function Format

substring(column_or_string, start_position, length);

Example

SELECT substring("abcdef", 3, 2)

When you run the example above, the following result is displayed.

cd

MySQL | Totals with WITH ROLLUP

kc@example.com (kc kim) — Mon, 07 Aug 2017 21:01:44 +0900

When you use GROUP BY, MySQL calculates totals for each column listed after GROUP BY.
One limitation is that you may also want the grand total to appear together with the subtotal for each item.

In that case, use WITH ROLLUP.

WITH ROLLUP is used to calculate totals for each group at once.

WITH ROLLUP Syntax

SELECT "field1", SUM("field2")
FROM "table_name"
GROUP BY "field1"
WITH ROLLUP

WITH ROLLUP Examples

store_information Table

region_name	store_name	sales
West	Los Angeles	1500
West	San Diego	250
West	Los Angeles	300
East	Boston	700

Assume the table above exists, and run the following statement.

SQL Example 1

SELECT store_name, SUM(sales)
FROM store_information
GROUP BY store_name
WITH ROLLUP

Result

store_name	SUM(sales)
Boston	700
Los Angeles	1800
San Diego	250
NULL	2750
The final row displays the total, `2750`.

SQL Example 2

SELECT region_name, store_name, SUM(sales)
FROM store_information
GROUP BY region_name, store_name
WITH ROLLUP

Result

region_name	store_name	SUM(sales)
East	Boston	700
East	NULL	700
West	Los Angeles	1800
West	San Diego	250
West	NULL	2050
NULL	NULL	2750

The second row displays the total for East, 700, and the fifth row displays the total for West, 2050.
The final row displays the grand total, 2750.

MySQL | Change the Sort Order of NULL Values

kc@example.com (kc kim) — Mon, 07 Aug 2017 21:01:44 +0900

When sorting with the ORDER BY clause, rows whose value is NULL may appear at the top.
This article explains how to handle that case.

Syntax

SELECT "field"
FROM "table_name"
ORDER BY "field" IS NULL [ASC|DESC]

Example

store_information Table

region_name	store_name	sales
West	Los Angeles	1500
West	San Diego	250
West	Los Angeles
East	Boston	700

SQL Example: NULL Is Sorted First

Assume the table above exists. If you write and run the following SQL statement:

SELECT store_name, sales
FROM store_information
ORDER BY sales ASC

the NULL value is sorted to the top as shown below.

store_name	sales
Los Angeles	NULL
San Diego	250
Boston	700
Los Angeles	1500

SQL Example: Sort NULL Last

To sort NULL values last, write and run the following SQL statement.

SELECT store_name, sales
FROM store_information
ORDER BY sales IS NULL ASC, sales ASC

The NULL value is sorted to the bottom as shown below.

store_name	sales
San Diego	250
Boston	700
Los Angeles	1500
Los Angeles	NULL