The ALTER TABLE statement is used to add, modify or drop columns in an existing table.
1. Add Column in an existing table:
Using ALTER TABLE statement you can add a new column in existing table.
- Add Single column:
Syntax: ALTER TABLE table_name ADD column_name datatype; Example: Alter Table Data Add Address varchar(100);
- Add multiple columns:
Syntax: ALTER TABLE table_name ADD column_1 datatype, column_2 datatype, ... column_n datatype; Example: ALTER TABLE Data ADD firstName varchar(100), LastName varchar(100), Town varchar(50);
2. Modify column in an existing table:
You can use the ALTER TABLE statement in SQL Server to modify a column in a table.
Syntax: ALTER TABLE table_name ALTER COLUMN column_name datatype; Example: ALTER TABLE Data ALTER COLUMN Town varchar(100); Earlier Town datatype was varchar(50), now it is varchar(100)
3. Drop column:
It is used to Drop a column in a table.
Syntax: ALTER TABLE table_name DROP COLUMN column_name; Example: ALTER TABLE Data DROP COLUMN Town; Note: Some database systems do not allow deleting a column from table.
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