MySQL add column if not exist

If your host doesn’t give you permission to create or run procedures, I think I found another way to do this using PREPARE/EXECUTE and querying the schema:

SET @s = (SELECT IF(
    (SELECT COUNT(*)
        FROM INFORMATION_SCHEMA.COLUMNS
        WHERE table_name="table_name"
        AND table_schema = DATABASE()
        AND column_name="col_name"
    ) > 0,
    "SELECT 1",
    "ALTER TABLE table_name ADD col_name VARCHAR(100)"
));

PREPARE stmt FROM @s;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;