In PostgreSQL, is there any performance gain when using a single ALTER TABLE statement to drop multiple columns, instead of using a separate statement to drop each column?
ALTER TABLE table DROP COLUMN col1, DROP COLUMN col2, DROP COLUMN 3;
// vs
ALTER TABLE table DROP COLUMN col1;
ALTER TABLE table DROP COLUMN col2;
ALTER TABLE table DROP COLUMN col3;
Yes, but it's too small to be noticed unless you plan to drop hundreds or even thousands of columns ;)
Each drop column is executed separately regardless if it's a separate statement, or part of a statement. The performance gain would be in the work postgres do before and after each statement, for instance taking a lock on the table, creating implicit transactions, and parsing the statement which it would only have to do once if all columns are dropped in one statement.
