How to write the default value of age in mysql

In MySQL, the methods to set the default value for the age column are: 1. Specify the default value when creating the table; 2. Use the DEFAULT keyword; 3. Use the UPDATE statement.

Age default value setting in MySQL

In MySQL, it is possible to set a default value for the age column in the table This is achieved through the following methods:

1. Specify the default value when creating the table

When creating the table, you can specify the default value in the column definition. For example:

<code>CREATE TABLE users (
  id INT NOT NULL AUTO_INCREMENT,
  name VARCHAR(255) NOT NULL,
  age INT NOT NULL DEFAULT 0
);</code>

In this way, the age column of all inserted records in the table will be set to 0 by default.

2. Use the DEFAULT keyword

You can also use the DEFAULT keyword later to add a default value to an existing column. For example:

<code>ALTER TABLE users ALTER COLUMN age SET DEFAULT 0;</code>

This will set the default value to 0 for the age column.

3. Use the UPDATE statement

You can also use the UPDATE statement to set default values ​​for existing records. For example:

<code>UPDATE users SET age = 0 WHERE age IS NULL;</code>

This will set the default value to 0 for all records with an empty age column.

Note:

• If no default value is specified, the value of the age column will be NULL.
• Default values ​​can only be set when creating a table or column and cannot be changed later.
• The default value can be a constant, expression or subquery, but cannot be a function.

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