For more information, refer to the Identity Columns sections.

However, the data type of the modified column should be appropriate else an error is displayed. When you modify an identity column and do not specify the modified column as an identity column, then the modified column still retains the identity column property.For information on the permissible expression for default value expr, refer to the Default Values section. If a default value is not specified, then any old default value that exists and which is appropriate to the new data type will be used. For example, in data types, BOOL cannot be converted to TIMESTAMP, and for the content of a column, if you have CHAR (3) with the content '123', then it can be converted to DECIMAL, however, if the content is 'ABC', it cannot be converted.Ī default value must be convertible to the data type. The data type and the content specified in the columns must be convertible.If the optional clause IF EXISTS is specified, then the statement does not throw an exception if the column does not exist.If the column that is dropped is a part of the partitioning key (see ALTER TABLE (Distribution/Partitioning) for more information), then the partitioning keys are dropped and the new rows of the table will not be partitioned any more.If the column that is dropped is a part of the distribution key (see ALTER TABLE (Distribution/Partitioning) for more information), then the distribution keys are dropped and the new rows of the table will be distributed randomly across the cluster nodes.When you specify this option, the foreign key reference to the column is deleted even when the referencing table does not belong to the current user. If a column that you need to delete has foreign key references, then specify the option CASCADE CONSTRAINTS.For information about constraints, refer to the ALTER TABLE (Constraints) section.If the clause IF NOT EXISTS is specified, then statement does not throw an error message if the column already exists.For more information, refer to the Identity Columns section.

For identity columns, a monotonically increasing number is generated if the table already possesses rows.For information on the permissible expressions for default value expr, refer to Default Values section. If the default value expression is not appropriate for the specified data type, an error message is displayed, and the statement is not executed.If the table already contains rows, the content of the inserted column will be set to the default value if it has been specified.

Postgresql alter table add column