## Synopsis Use the `ALTER TABLE` statement to change the schema or definition of an existing table. It allows adding, dropping, or renaming a column as well as updating a table property. ## Syntax ### Diagram ### Grammar ```ebnf alter_table ::= ALTER TABLE table_name alter_operator [ alter_operator ...] alter_operator ::= add_op | drop_op | rename_op | property_op add_op ::= ADD column_name column_type [ ',' column_name column_type ...] drop_op ::= DROP column_name [ ',' column_name ...] rename_op ::= RENAME column_name TO column_name [ ',' column_name TO column_name ...] property_op ::= WITH property_name '=' property_literal [ AND property_name '=' property_literal ...] ``` Where - `table_name`, `column_name`, and `property_name` are identifiers (`table_name` may be qualified with a keyspace name). - `property_literal` is a literal of either [boolean](../type_bool), [text](../type_text), or [map](../type_collection) data type. ## Semantics - An error is raised if `table_name` does not exist in the associated keyspace. - Columns that are part of `PRIMARY KEY` cannot be altered. - When adding a column, its value for all existing rows in the table defaults to `null`. - After dropping a column, all values currently stored for that column in the table are discarded (if any). ## Examples ### Add a column to a table ```sql ycqlsh:example> CREATE TABLE employees (id INT, name TEXT, salary FLOAT, PRIMARY KEY((id), name)); ``` ```sql ycqlsh:example> ALTER TABLE employees ADD title TEXT; ``` ```sql ycqlsh:example> DESCRIBE TABLE employees; ``` Following result would be shown. ```output CREATE TABLE example.employees ( id int, name text, salary float, title text, PRIMARY KEY (id, name) ) WITH CLUSTERING ORDER BY (name ASC); ``` ### Remove a column from a table ```sql ycqlsh:example> ALTER TABLE employees DROP salary; ``` ```sql ycqlsh:example> DESCRIBE TABLE employees; ``` Following result would be shown. ```output CREATE TABLE example.employees ( id int, name text, title text, PRIMARY KEY (id, name) ) WITH CLUSTERING ORDER BY (name ASC); ``` ### Rename a column in a table ```sql ycqlsh:example> ALTER TABLE employees RENAME title TO job_title; ``` ```sql ycqlsh:example> DESCRIBE TABLE employees; ``` Following result would be shown. ```output CREATE TABLE example.employees ( id int, name text, job_title text, PRIMARY KEY (id, name) ) WITH CLUSTERING ORDER BY (name ASC); ``` ### Update a table property You can do this as follows: ```sql ycqlsh:example> ALTER TABLE employees WITH default_time_to_live = 5; ``` ```sql ycqlsh:example> DESCRIBE TABLE employees; ``` Following result would be shown. ```output CREATE TABLE example.employees ( id int, name text, job_title text, PRIMARY KEY (id, name) ) WITH CLUSTERING ORDER BY (name ASC) AND default_time_to_live = 5; ``` ## See also - [`CREATE TABLE`](../ddl_create_table) - [`DELETE`](../dml_delete/) - [`DROP TABLE`](../ddl_drop_table) - [`INSERT`](../dml_insert) - [`SELECT`](../dml_select/) - [`UPDATE`](../dml_update/)