How to set default values ​​when adding columns in SQL

Set the default value for newly added columns, use the ALTER TABLE statement: Specify adding columns and set the default value: ALTER TABLE table_name ADD column_name data_type DEFAULT default_value; use the CONSTRAINT clause to specify the default value: ALTER TABLE table_name ADD COLUMN column_name data_type CONSTRAINT default_constraint DEFAULT default_value;

Set default values ​​for newly added columns

In SQL, the steps to set default values ​​for newly added columns are as follows:

1. Use ALTER TABLE statement

The syntax for adding columns and setting default values ​​is as follows:

 <code class="sql">ALTER TABLE table_name ADD column_name data_type DEFAULT default_value;</code>

in:

• table_name is the table name to add the column.
• column_name is the name of the new column to be added.
• data_type is the data type of the new column.
• default_value is the default value for the new column.

2. Use CONSTRAINT clause

You can also use the CONSTRAINT clause to specify the default value:

 <code class="sql">ALTER TABLE table_name ADD COLUMN column_name data_type CONSTRAINT default_constraint DEFAULT default_value;</code>

in:

• default_constraint is the name of the constraint (can be any name).

3. Example

For example, to add a column named age to a table named users and set the default value to 25 , you can use the following statement:

 <code class="sql">ALTER TABLE users ADD COLUMN age INT DEFAULT 25;</code>

Doing so will add a new column named age to the users table, with the data type of integer and the default value is 25 .

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