Support for IF NOT EXISTS in ALTER TABLE ADD COLUMN Statements Along with IF EXISTS in Drop/modify/clear/comment COLUMN

Why it matters

This feature helps prevent errors during schema changes by allowing conditional execution of ALTER TABLE operations. It avoids failures when adding a column that already exists or modifying/dropping a column that might not exist, thereby improving the robustness and user experience of schema migrations.

How to use it

Users can add the clause IF NOT EXISTS when adding a new column:

ALTER TABLE table_name ADD COLUMN IF NOT EXISTS column_name <datatype>;

For dropping, modifying, clearing, or commenting on columns, use IF EXISTS:

ALTER TABLE table_name DROP COLUMN IF EXISTS column_name;
ALTER TABLE table_name MODIFY COLUMN IF EXISTS column_name <datatype>;
ALTER TABLE table_name CLEAR COLUMN IF EXISTS column_name;
ALTER TABLE table_name COMMENT COLUMN IF EXISTS column_name 'comment';