What is the syntax for adding columns in SQL

The syntax for adding columns in SQL is ALTER TABLE table_name ADD column_name data_type [NOT NULL] [DEFAULT default_value]; where table_name is the table name, column_name is the new column name, data_type is the data type, NOT NULL specifies whether null values ​​are allowed, and DEFAULT default_value specifies the default value.

SQL syntax for adding columns

In SQL, use the ALTER TABLE statement to add a new column to an existing table. The syntax is as follows:

 <code class="sql">ALTER TABLE table_name ADD column_name data_type [NOT NULL] [DEFAULT default_value];</code>

in:

• table_name is the table name to add the column.
• column_name is the new column name to be added.
• data_type is the data type of the new column, such as INT , VARCHAR , DATE , DECIMAL , etc.
• NOT NULL specifies whether the column allows null values.
• DEFAULT default_value specifies the default value for this column, and NULL if no value is specified.

Example

For example, to add a new column named email to the customers table, you can execute the following statement:

 <code class="sql">ALTER TABLE customers ADD COLUMN email VARCHAR(255) NOT NULL DEFAULT '';</code>

This will add a new column named email to the customers table, with data type VARCHAR(255) , no null values ​​are allowed, and the default value is an empty string.

The above is the detailed content of What is the syntax for adding columns in SQL. For more information, please follow other related articles on the PHP Chinese website!