SELECT work_start from `work` WHERE work_start=CONCAT(DATE_FORMAT('2022-01-01 8:00', '%W%H:%i')) AS weekday_time;哪里错了

这个 SQL 查询语句有语法错误。应该将 AS weekday_time 放在 FROM 子句之后，而不是放在 WHERE 子句之后。正确的 SQL 查询语句应该是：

SELECT work_start as weekday_time 
FROM `work` 
WHERE work_start = CONCAT(DATE_FORMAT('2022-01-01 8:00', '%W %H:%i'));

这个查询语句的作用是从 `work` 表中查询 `work_start` 字段等于 '2022-01-01 8:00' 当天的星期和时间，并将结果赋值给别名 `weekday_time`。注意，星期和时间之间应该有一个空格，否则 CONCAT 函数会将它们拼接在一起。

相关问题

begin if work_start FROM work where work_start=CONCAT(DATE_FORMAT(r_time, '%W%H:%i')) then insert into reserve(New.r_id,p_id,d_id,r_time,'已预约',null); else SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Data does not meet the requirements'; end if; end有错

这段代码中的错误在于缺少了一个关键字 `SELECT`，导致无法正确从 `work` 表中获取到工作开始时间。正确的代码应该是：

BEGIN
    IF (SELECT work_start FROM work WHERE work_start = CONCAT(DATE_FORMAT(r_time, '%W%H:%i'))) THEN
        INSERT INTO reserve (New.r_id, p_id, d_id, r_time, status, note) VALUES (New.r_id, New.p_id, New.d_id, New.r_time, '已预约', null);
    ELSE
        SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Data does not meet the requirements';
    END IF;
END;

这样修改后，代码应该就可以正常执行了。

BEGIN IF (SELECT work_start FROM work WHERE work_start = CONCAT(DATE_FORMAT(r_time, '%W%H:%i'))) THEN INSERT INTO reserve (New.r_id, p_id, d_id, r_time, status, null) VALUES (New.r_id, New.p_id, New.d_id, New.r_time, '已预约', null); ELSE SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Data does not meet the requirements'; END IF; DECLARE count INT; SELECT COUNT(*) into count from reserve where r_time=NEW.r_time AND d_id=NEW.id; SELECT renshu into @num from work where d_id=NEW.id AND work_start = CONCAT(DATE_FORMAT(NEW.r_time, '%W%H:%i'))); IF count<=@num then update reserve set New.r_out_num=@num-count doctor_id = NEW.doctor_id AND CONCAT(DATE_FORMAT(NEW.r_time, '%W%H:%i'))); else SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Appointment limit exceeded'; END IF; END有语法错误

根据你提供的代码，发现有一些语法错误。首先，第一个 IF 语句中的 SELECT 语句缺少 FROM 子句，应该指定查询的表名。其次，在第一个 IF 语句中的 INSERT INTO 语句中，VALUES 子句中缺少一列的值，应该指定 r_out_num 的值。最后，第二个 SELECT 语句中的 doctor_id 和 CONCAT 函数之间应该用逗号分隔，而不是 AND。下面是修正后的代码：

BEGIN
IF (SELECT work_start FROM work WHERE work_start = CONCAT(DATE_FORMAT(r_time, '%W%H:%i')) FROM work) THEN
INSERT INTO reserve (New.r_id, p_id, d_id, r_time, status, r_out_num) VALUES (New.r_id, New.p_id, New.d_id, New.r_time, '已预约', null);
ELSE
SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Data does not meet the requirements';
END IF;

DECLARE count INT;
SELECT COUNT(*) INTO count FROM reserve WHERE r_time=NEW.r_time AND d_id=NEW.id;

SELECT renshu INTO @num FROM work WHERE d_id=NEW.id AND work_start = CONCAT(DATE_FORMAT(NEW.r_time, '%W%H:%i'));

IF count <= @num THEN
UPDATE reserve SET r_out_num=@num-count, doctor_id=NEW.doctor_id, r_time=CONCAT(DATE_FORMAT(NEW.r_time, '%W%H:%i'));
ELSE
SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Appointment limit exceeded';
END IF;
END