How to use modify in sql

The MODIFY command in SQL is used to modify the table structure, including adding columns, deleting columns, modifying column data types, modifying column default values, and modifying whether columns can be null.

Use of MODIFY in SQL

The MODIFY command is used in SQL to modify the table structure, specifically , it can be used for:

1. Add column

<code class="sql">ALTER TABLE table_name ADD COLUMN new_column_name data_type;</code>

2. Delete column

<code class="sql">ALTER TABLE table_name DROP COLUMN column_name;</code>

3 . Modify the column data type

<code class="sql">ALTER TABLE table_name ALTER COLUMN column_name SET DATA TYPE new_data_type;</code>

4. Modify the column default value

<code class="sql">ALTER TABLE table_name ALTER COLUMN column_name SET DEFAULT default_value;</code>

5. Modify whether the column can be empty

<code class="sql">ALTER TABLE table_name ALTER COLUMN column_name SET NOT NULL;
ALTER TABLE table_name ALTER COLUMN column_name SET NULL;</code>

Instructions for use:

• The MODIFY command is part of the ALTER TABLE statement, so it must be used after the ALTER TABLE statement.
• table_name is the name of the table to be modified.
• column_name is the column name to be modified.
• new_column_name is the name of the newly added column.
• data_type is the data type of a newly added column or modified column.
• default_value is the default value for newly added columns or modified columns.

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