Tutorial by Examples

PREPARE prepares a statement for execution EXECUTE executes a prepared statement DEALLOCATE PREPARE releases a prepared statement SET @s = 'SELECT SQRT(POW(?,2) + POW(?,2)) AS hypotenuse'; PREPARE stmt2 FROM @s; SET @a = 6; SET @b = 8; EXECUTE stmt2 USING @a, @b; Result: +------------+ |...

(This is a request for a good example that shows how to construct a SELECT using CONCAT, then prepare+execute it. Please emphasize the use of @variables versus DECLAREd variables -- it makes a big difference, and it is something that novices (include myself) stumble over.)

SET v_column_definition := CONCAT( v_column_name ,' ',v_column_type ,' ',v_column_options ); SET @stmt := CONCAT('ALTER TABLE ADD COLUMN ', v_column_definition); PREPARE stmt FROM @stmt; EXECUTE stmt; DEALLOCATE PREPARE stmt;