Question

我有这样的查询

SELECT hc_num,client_pow,client_id,date_issued,client_occup 
FROM tbl_health_certificate t1 
WHERE date_issued = 
    (SELECT MAX(date_issued) 
     FROM tbl_health_certificate t2 
     WHERE t2.client_id=t1.client_id) AND year(date_issued) < year(now())

现在我希望将结果连接到另一个表，以获取某些行值，尤其是client_fname和client_lname字段。我该怎么做？：）

我的表格结构如下 - ＆gt; tbl_health_certificate，[tbl_client] [2]

Content of tbl_health_certificate

应显示的结果是带有client_id的行： -26 -29

使用表tbl_client

中的client_fname和client_lname

Answer 1

好吧，经过一夜的睡眠，我明白为什么我昨天的答案不起作用。我认为子查询是不必要的，但我错了，因为聚合列中的值不一定来自与MAX(tbl_health_certificate.date_issued)相同的行。此外，我困倦的头脑没有意识到WHERE在分组发生之前缩小了结果，所以这确实会导致来自今年最近一行的客户的行显示出来。 “不是来自今年”的条件应该放在HAVING条款中，正如我在下面所做的那样。

此查询的嵌套级别低于OP自己的解决方案，因此我认为这是一个很好的选择。

SELECT t1.hc_num, t1.client_pow, t1.client_id,
    t1.date_issued, t1.client_occup, t4.client_fname, t4.client_lname
FROM tbl_health_certificate t1
JOIN
    (SELECT t2.client_id, MAX(t2.date_issued) AS max_date
    FROM tbl_health_certificate t2
    GROUP BY t2.client_id
    HAVING year(MAX(t2.date_issued)) < year(now())) t3
ON t1.client_id = t3.client_id AND t1.date_issued = t3.max_date
JOIN tbl_client t4 ON t1.client_id = t4.client_id

Answer 2

修改了几行。

select table1.* , table2.* from
(SELECT hc_num,client_pow,client_id,date_issued,client_occup 
FROM tbl_health_certificate t1,
(SELECT MAX(date_issued) date_issued_max
     FROM tbl_health_certificate t2 group by client_id) t2
WHERE t1.date_issued = t2.date_issued_max
AND year(date_issued) < year(now())) table1
left/right/full outer join -- use appropriate join
tbl_client table2 ON table1.client_id = table2.client_id

Answer 3

我相信查询会是这样的：

SELECT 
t2.client_fname, t2.client_lname, t1.hc_num, t1.client_pow,
t1.client_id, MAX(t1.date_issued) as 'date_issued', t1.client_occup 
FROM tbl_health_certificate t1 INNER JOIN 
tbl_client t2 ON t2.client_id = t1.client_id
WHERE year(t1.date_issued) < year(now())
GROUP BY t1.client_id

带有GROUP BY的MAX会有所帮助，然后t1的任何行结果会立即加入tbl_client以检索客户端信息。

相关查询的内连接结果

3 个答案: