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SQL: ALTER TABLE |
The ALTER TABLE statement allows to change the structure of a table after it has been created. New columns can be added with the ADD clause. Existing columns may be removed from a table using the Drop clause. The syntax of the ALTER TABLE statement is as follows: ALTER TABLE table_name
ADD column_name data_type ALTER TABLE table_name DROP COLUMN column_name Note: The ALTER TABLE statement is not part of ANSI/ISO standard. This means that all the commercial dialects of SQL implement different clauses and command syntax. Example #1ALTER TABLE Orders
ADD Quantity SMALLINT This example adds a single column to the "Orders" table by specifying the new column name and data type. Example #2ALTER TABLE EmployeeAddressTable
ADD Description VARCHAR(20) DEFAULT 'USA' NOT NULL This example adds a column named "Description" to the "EmployeeAddressTable" table. We also add the reserved words NOT NULL to require valid data to be added to that column and specify a default value. Example #3ALTER TABLE AntiqueOwners DROP COLUMN State
This example drops the "State" column from the "AntiqueOwners" table. |
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