Altering a Table

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ALTER TABLE enables the following changes to an existing table:

  • Adding new column definitions
  • Adding new table constraints
  • Dropping existing column definitions
  • Dropping existing table constraints
  • Changing column definitions by dropping existing definitions, and adding new ones
  • Changing existing table constraints by dropping existing definitions, and adding new ones
  • Modifying column names and data types

The simple syntax of ALTER TABLE is as follows:

ALTER TABLE name {ADD colname <data_type> [NOT NULL]
| ALTER [COLUMN] simple_column_name alter_rel_field

 | DROP colname | ADD CONSTRAINT constraintname tableconstraint
| DROP CONSTRAINT constraintname};
For information about adding, dropping, and modifying constraints at the table level, see the Data Definition Guide.

For the complete syntax of ALTER TABLE, see the Language Reference Guide.


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