MySQL CREATE TABLE

 

MySQL CREATE TABLE


Summaryin this tutorial, we will show you how to use the MySQL CREATE TABLE statement to create a new table in the database.

MySQL CREATE TABLE syntax

The CREATE TABLE the statement allows you to create a new table in a database.

The following illustrates the basic syntax of the CREATE TABLE  statement:

CREATE TABLE [IF NOT EXISTS] table_name( column_1_definition, column_2_definition, ..., table_constraints ) ENGINE=storage_engine;

Let’s examine the syntax in greater detail.

First, you specify the name of the table that you want to create after the CREATE TABLE  keywords. The table name must be unique within a database. The IF NOT EXISTS is optional. It allows you to check if the table that you create already exists in the database. If this is the case, MySQL will ignore the whole statement and will not create any new table.

Second, you specify a list of columns of the table in the column_list section, columns are separated by commas.

Third, you can optionally specify the storage engine for the table in the ENGINE clause. You can use any storage engine such as InnoDB and MyISAM. If you don’t explicitly declare a storage engine, MySQL will use InnoDB by default.

InnoDB became the default storage engine since MySQL version 5.5. The InnoDB storage engine brings many benefits of a relational database management system such as ACID transaction, referential integrity, and crash recovery. In the previous versions, MySQL used MyISAM as the default storage engine.

The following shows the syntax for a column’s definition:

column_name data_type(length) [NOT NULL] [DEFAULT value] [AUTO_INCREMENT] column_constraint;

Here are the details:

  • Thecolumn_name specifies the name of the column. Each column has a specific data type and optional size e.g.,VARCHAR(255) 
  • The  NOT NULL constraint ensures that the column will not contain NULL. Besides the NOT NULL constraint, a column may have additional constraints such as CHECK, and UNIQUE.
  • The DEFAULT specifies a default value for the column.
  • The AUTO_INCREMENT  indicates that the value of the column is incremented by one automatically whenever a new row is inserted into the table. Each table has a maximum one AUTO_INCREMENT column.

After the column list, you can define table constraints such as UNIQUECHECKPRIMARY KEY, and FOREIGN KEY.

For example, if you want to set a column or a group of columns as the primary key, you use the following syntax:

PRIMARY KEY (col1,col2,...)

MySQL CREATE TABLE statement examples

Let’s take some examples of creating new tables.

1) MySQL CREATE TABLE simple example

The following statement creates a new table named tasks:

CREATE TABLE IF NOT EXISTS tasks ( task_id INT AUTO_INCREMENT PRIMARY KEY, title VARCHAR(255) NOT NULL, start_date DATE, due_date DATE, status TINYINT NOT NULL, priority TINYINT NOT NULL, description TEXT, created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ) ENGINE=INNODB;

The tasks table has the following columns:

  • The task_id is an auto-increment column. If you use the INSERT statement to insert a new row into the table without specifying a value for the task_id column, MySQL will automatically generate a sequential integer for the task_id starting from 1.
  • The title the column is a variable character string column whose maximum length is 255. It means that you cannot insert a string whose length is greater than 255 into this column. The NOT NULL constraint indicates that the column does not accept NULL. In other words, you have to provide a non-NULL value when you insert or update this column.
  • The start_date and due_date are DATE columns. Because these columns do not have the NOT NULL constraint, they can store NULL. The start_date column has a default value of the current date. In other words, if you don’t provide a value for the start_date column when you insert a new row, the start_date column will take the current date of the database server.
  • The status and priority are the TINYINT columns which do not allow NULL.
  • The description column is a TEXT column that accepts NULL.
  • The created_at is a TIMESTAMP the column that accepts the current time as the default value.

The task_id is the primary key column of the tasks table. It means that the values in the task_id column will uniquely identify rows in the table.

Once you execute the CREATE TABLE statement to create the tasks table, you can view its structure by using the DESCRIBE statement:

DESCRIBE tasks;
MySQL CREATE TABLE - DESCRIBE table

This picture shows the database diagram of the tasks table:

MySQL CREATE TABLE - Tasks table

2) MySQL CREATE TABLE with a foreign key primary key example

Suppose each task has a checklist or to-do list. To store checklists of tasks, you can create a new table named checklists as follows:

CREATE TABLE IF NOT EXISTS checklists ( todo_id INT AUTO_INCREMENT, task_id INT, todo VARCHAR(255) NOT NULL, is_completed BOOLEAN NOT NULL DEFAULT FALSE, PRIMARY KEY (todo_id , task_id), FOREIGN KEY (task_id) REFERENCES tasks (task_id) ON UPDATE RESTRICT ON DELETE CASCADE );

The table checklists has a primary key that consists of two columns. Therefore, we used a table constraint to define the primary key:

PRIMARY KEY (todo_id , task_id)

In addition, the task_id is the foreign key column that references to the task_id a column of the table tasks, we used a foreign key constraint to establish this relationship:

FOREIGN KEY (task_id) REFERENCES tasks (task_id) ON UPDATE RESTRICT ON DELETE CASCADE

You will learn more about the foreign key constraint in the subsequent tutorial.

This picture illustrates the checklists table and its relationship with the tasks table:

MySQL CREATE TABLE - checklists table

In this tutorial, you have learned how to use MySQL CREATE TABLE statement to create a new table in the database

Reactions

Post a Comment

0 Comments