ALTER TABLE Command

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ALTER TABLE Command

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ALTER TABLE allows you to change the structure of an existing table.

Syntax

ALTER TABLE [ MEMORY ] table_name alter_specification

where alter_specification is:

ADD ( [ [ IF NOT EXISTS ] column_definition ] [, ... ] [ index_definition ] [, ... ] )

| MODIFY ( [ column_definition ] [, ... ] )

| DROP ( [ column_name ] [, ... ] )  

| RENAME [ COLUMN ] old_column_name [ TO ] new_column_name  

| RENAME [ TABLE ] [ TO ] new_table_name  

 

Description

ALTER TABLE allows you to change the structure of an existing table. For example, you can add or delete columns, create indexes, change the type of existing columns, or rename columns or the table itself.

 

MEMORY

If MEMORY keyword is specified before the table_name then an in-memory table will be altered, not a disk one.

 

table_name

The name of the table to be altered.

 

ADD

Adds the new column(s) and index(es) using the same syntax as CREATE TABLE.

 

IF NOT EXISTS

If this keyword is specified, the coulmn will be created, only if there is no existing column with the same name. If this keyword is not specified and the column already exists, an exception will be raised.

 

MODIFY

Changes the column(s) settings such as data type, size, default value, etc..

 

DROP

Deletes the specified column(s).

 

RENAME COLUMN

Changes a name of a column to the new_column_name value.  

 

RENAME TABLE

Changes a name of a table to the new_table_name value.

 

Example:

ALTER TABLE employee ADD (height Float);

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Absolute SQL Reference - 06 February 2021, Niels Knabe