查询以从一个表和一个额外的 col 检索信息，这是另一个表的条件

Question

我有一个工人表和一个关联的卡片表：

CREATE TABLE IF NOT EXISTS `workers` (
  `ID` varchar(20) NOT NULL,
  `companyID` int(11) NOT NULL,
  `FName` varchar(25) NOT NULL,
  `Sname` varchar(25) NOT NULL,
  `isAvailable` tinyint(4) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

ALTER TABLE `workers`
 ADD PRIMARY KEY (`ID`), ADD KEY `cmp_idx` (`companyID`), ADD KEY `isAvailable_idx` (`isAvailable`);

我需要检索一份工人名单，每个工人都有一个指示他们的卡是否未获批准。

卡片表如下：

CREATE TABLE IF NOT EXISTS `cards2` (
`ID` int(11) NOT NULL,
  `Name` varchar(200) NOT NULL,
  `WorkerID` varchar(20) NOT NULL,
  `pic` varchar(200) NOT NULL,
  `expDate` bigint(20) NOT NULL,
  `reminderSent` tinyint(4) NOT NULL,
  `regNum` varchar(8) NOT NULL,
  `cardType` varchar(200) NOT NULL,
  `approvalStatus` tinyint(4) NOT NULL
) ENGINE=MyISAM AUTO_INCREMENT=95 DEFAULT CHARSET=latin1;

ALTER TABLE `cards2`
 ADD PRIMARY KEY (`ID`), ADD KEY `cardsWorkerID_idx` (`WorkerID`);

approvalStatus 可以是 2（尚未确定）、1（已批准）或 2（未批准） 因此，返回的指示符应仅在所有卡片均已获批准时为绿色 (1)，如果任何卡片尚未获批准或未获批准，则应为红色 (0)。

检索工人的查询很简单：

SELECT distinct Workers.ID, FName, SName, companyID
FROM Workers WHERE companyID = ? and  
and isAvailable = 1
LIMIT ?, 10

在尝试取回卡片指示器时，我尝试了以下操作：

    SELECT Workers.ID, FName, SName, 
COUNT(CASE WHEN approvalStatus = 0 or approvalStatus = 2 THEN 1 ELSE 0 end) AS cardStatus 
FROM `workers` 
inner join cards2 ON Workers.ID = Cards2.WorkerID 
WHERE workers.companyID = 1

这只是返回一名工人

更新 如果用户没有关联的卡片，它还应该标记红色状态

Answer 1

您可以通过EXISTS 询问用户是否存在开放或未批准的卡：

select id, fname, sname, companyid,
  case when exists 
  (
    select * 
    from cards2 c
    where c.workerid = w.id
    and c.approvalstatus in (0,2)
  ) then then 'red' else 'green' end as status
from workers w 
where companyid = ?
and isavailable = 1;

更新：这里是对没有卡 = 红色的附加要求的查询：

select id, fname, sname, companyid,
  case when exists 
  (
    select * 
    from cards2 c
    where c.workerid = w.id
    and c.approvalstatus in (0,2)
  )
  or not exists 
  (
    select * 
    from cards2 c
    where c.workerid = w.id
  ) then then 'red' else 'green' end as status
from workers w 
where companyid = ?
and isavailable = 1;

这与聚合的状态和使用 MySQL 三布尔逻辑相同：

select w.id, w.fname, w.sname, w.companyid,
  case when not c.bad then 'green' else 'red' end as status
from 
(
  select 
    workerid,
    max(case when approvalstatus in (0,2) then 1 else 0 end) as bad
  from cards2
  group by workerid
) c
from workers w 
where w.companyid = ? and  
and w.isavailable = 1;