约束MySQL字符串列仅包含字母和不包含字母

CREATE TABLE foobar(
    id          SMALLINT   UNSIGNED  NOT   NULL PRIMARY KEY,
    no_alpha    VARCHAR(6)   NOT   NULL,
    some_alpha  VARCHAR(6)   NOT   NULL,
    all_alpha   VARCHAR(6)   NOT   NULL
);

-- -- 创建表数据插入前的触发器
CREATE TRIGGER check_valid_i BEFORE INSERT ON foobar FOR EACH ROW
BEGIN 
	DECLARE all_alpha, no_alpha, not_all_alpha, not_no_alpha INT;
	SET not_all_alpha = 0, not_no_alpha = 0;
	IF NOT (NEW.all_alpha REGEXP '^[A-Za-z]+$') THEN SET not_all_alpha = 1; 
	END IF;
	IF NOT (NEW.no_alpha REGEXP '^[^A-Za-z]+$') THEN SET not_no_alpha = 1;
	END IF;
	IF not_all_alpha = 1 AND not_no_alpha = 1 THEN 
		SELECT CONCAT('Can not INSERT this, because ', NEW.all_alpha, ' is invalid'), 
		    CONCAT('Can not INSERT this, because ', NEW.no_alpha, ' is invalid')
		INTO all_alpha, no_alpha FROM information_schema.tables;
	END IF;
	IF not_all_alpha = 1 THEN 
		SELECT CONCAT('Can not INSERT this, because ', NEW.all_alpha, ' is invalid')
		INTO all_alpha FROM information_schema.tables;
	END IF;
	IF not_no_alpha = 1 THEN 
		SELECT CONCAT('Can not INSERT this, because ', NEW.no_alpha, ' is invalid')
		INTO not_no_alpha FROM information_schema.tables;
	END IF;
END; 

-- 创建表数据更新前的触发器
CREATE TRIGGER check_valid_u BEFORE UPDATE ON foobar FOR EACH ROW
BEGIN 
	DECLARE all_alpha, no_alpha, not_all_alpha, not_no_alpha INT;
	SET not_all_alpha = 0, not_no_alpha = 0;
	IF NOT (NEW.all_alpha REGEXP '^[A-Za-z]+$') THEN SET not_all_alpha = 1; 
	END IF;
	IF NOT (NEW.no_alpha REGEXP '^[^A-Za-z]+$') THEN SET not_no_alpha = 1;
	END IF;
	IF not_all_alpha = 1 AND not_no_alpha = 1 THEN 
		SELECT CONCAT('Can not UPDATE this, because ', NEW.all_alpha, ' is invalid'), 
		    CONCAT('Can not UPDATE this, because ', NEW.no_alpha, ' is invalid')
		INTO all_alpha, no_alpha FROM information_schema.tables;
	END IF;
	IF not_all_alpha = 1 THEN 
		SELECT CONCAT('Can not UPDATE this, because ', NEW.all_alpha, ' is invalid')
		INTO all_alpha FROM information_schema.tables;
	END IF;
	IF not_no_alpha = 1 THEN 
		SELECT CONCAT('Can not UPDATE this, because ', NEW.no_alpha, ' is invalid')
		INTO not_no_alpha FROM information_schema.tables;
	END IF;
END;