MySQL 列がまだ存在しない場合にのみ追加する方法

DELIMITER $$

DROP PROCEDURE IF EXISTS add_column_if_not_exists $$
CREATE PROCEDURE add_column_if_not_exists()
BEGIN

-- Check if the column exists
IF NOT EXISTS(
  SELECT *
  FROM information_schema.COLUMNS
  WHERE TABLE_SCHEMA=DATABASE()
    AND TABLE_NAME='table_name'
    AND COLUMN_NAME='new_column_name'
) THEN
  -- Alter the table to add the column
  ALTER TABLE table_name ADD new_column_name data_type NOT NULL DEFAULT value;
END IF;

END $$

CALL add_column_if_not_exists() $$

DELIMITER ;