Update the attribute columns of a mapping table - Tablestore

You can execute the ALTER TABLE statement to add or remove an attribute column in an existing mapping table.

Note

For information about how to create a mapping table, see Create a mapping table for a table.

Usage notes

You can execute the ALTER TABLE statement to update an attribute column in only a mapping table that is created by executing the CREATE TABLE statement. You cannot execute the ALTER TABLE statement to update an attribute column in a mapping table that is automatically created for a table by executing the DESCRIBE statement.
You can add or remove only one attribute column in a mapping table by executing the ALTER TABLE statement. If you want to add or remove multiple attribute columns in a mapping table, you can execute the ALTER TABLE statement multiple times.
You can execute the ALTER TABLE statement to update only the schema of a mapping table. The schema of the Tablestore table for which the mapping table is created is not updated.
You cannot execute the ALTER TABLE statement to add or remove the primary key columns in a mapping table.
After you execute the ALTER TABLE statement, the SQL engine asynchronously refreshes the mapping table. Up to 30 seconds are required to complete the refresh. During the refresh period, the column that you added may not be returned when you perform the operations that are supposed to return all columns.

ALTER TABLE table_name option column_name [data_type];

Parameter	Required	Description
table_name	Yes	The name of the mapping table, which is used to identify the mapping table.
option	Yes	The update operation that you want to perform. Valid values: ADD COLUMN: adds an attribute column to the mapping table. DROP COLUMN: removes an attribute column from the mapping table.
column_name	Yes	The name of the attribute column. The name of the attribute column that you want to add must be different from the names of existing attribute columns in the mapping table. The column name in SQL must be equivalent to the column name in the Tablestore table. For example, if the column name in the Tablestore table is Aa, the column name in SQL must be Aa, AA, aA, or aa.
data_type	No	The data type of the attribute column, such as BIGINT, DOUBLE, or BOOL. This parameter is required only if you set option to ADD COLUMN. The data type of the column in SQL must match the data type of the column in the Tablestore table. For information about data type mappings, see Data type mappings in SQL.

Add attribute columns to a mapping table
You can execute the following statements to add the colvalue attribute column and the content attribute column to the exampletable mapping table. The data type of the colvalue attribute column is BIGINT and the data type of the content attribute column is MEDIUMTEXT:
```
ALTER TABLE exampletable ADD COLUMN colvalue BIGINT;
```
```
ALTER TABLE exampletable ADD COLUMN content MEDIUMTEXT;
```
Remove an attribute column from a mapping table
You can execute the following statement to remove the colvalue column of the BIGINT type from the exampletable mapping table:
```
ALTER TABLE exampletable DROP COLUMN colvalue;
```