DO

PostgreSQL

Example

DO
$do$
BEGIN
    IF EXISTS (SELECT 1 FROM information_schema.tables WHERE table_name = 'test') THEN
        RAISE NOTICE 'Table exists.';
    ELSE
        RAISE NOTICE 'Table does not exist.';
    END IF;
END
$do$;

Output

NOTICE:  Table does not exist.

Explanation

The DO statement in PostgreSQL executes an anonymous code block, which does not need to be stored in the database. The example statement checks if a table named test exists in the database. If it exists, it outputs the message ‘Table exists.’, otherwise it outputs ‘Table does not exist.’.

MySQL

Example

DO SELECT CURRENT_DATE;

Output

No result set returned.

Explanation

The DO statement in MySQL is used to execute an expression or command but does not provide any output. In the provided example, although the CURRENT_DATE function is being called, no result is returned due to the nature of the DO statement. In contrast, if we used SELECT CURRENT_DATE; without the DO, MySQL would return the current date. It should be noted that in practical applications, the DO statement is typically used with expressions that have side-effects (e.g., storing values to variables), as it does not provide any results.