如何连接仍保留主表中所有值的表

Question

我有 3 个表，但现在我只使用 2 个进行测试

帐户表

         id     accnt      amount       date
        ---------------------------------------
         1       xxx        10.00      1/1/2016
         2       yyy        20.00      1/1/2016
         3       zzz        30.00      1/1/2016

已发行表

         id     accnt      issued       dateIssue
        ------------------------------------------
         1       xxx        5.00        1/10/2016
         1       xxx        5.00        2/14/2016
         2       yyy       10.00        2/15/2016  

我希望结果看起来像这样......如果在一月份

        id     accnt       amount    issued    balance  
      -------------------------------------------------
         1      xxx         10.00     5.00      5.00
         2      yyy         20.00     0.00     20.00
         3      zzz         30.00     0.00     30.00

如果是在二月

       id     accnt        amount    issued    balance
      -------------------------------------------------
        1       xxx         10.00     10.00     0.00
        2       yyy         20.00     10.00    10.00
        3       zzz         30.00      0.00    30.00

这是我提出的查询

       SELECT   AccntTbl.id, AccntTbl.accnt, AccntTbl.amount, 
                SUM(IssuedTbl.issued) as issued 
       FROM     AccntTbl LEFT JOIN IssuedTbl 
       ON       AccntTbl.id = IssuedTbl.id
       WHERE    (MONTH(IssuedTbl.dateIssue BETWEEN 1 AND 2)) AND
                (YEAR(AccntTbl.date)= 2016)
       GROUP BY AccntTbl.id, AccntTbl.accnt, AccntTbl.amount

但结果不是我所期望的，只有来自 1 & 2 的 id 会从结果中显示出来。我想显示 AccntTbl 中的所有值及其来自 IssuedTbl 的值。很高兴得到任何帮助。 .tnx :)

Answer 1

当您使用LEFT OUTER JOIN 并且想要从Right 表中过滤一些记录时，您需要将右表filter 移动到ON 条件否则@ 987654323@ 将隐式转换为INNER JOIN

简而言之，WHERE 子句reject 带有NULL 的行，这些行由LEFT OUTER JOIN 生成，用于不匹配的记录

SELECT A.id, 
       A.accnt, 
       A.amount, 
       Sum(I.issued) AS issued 
FROM   accnttbl A
       LEFT JOIN issuedtbl I
              ON A.id = I.id 
                 AND Month(I.dateissue) BETWEEN 1 AND 2 -- Right table filter
WHERE  Year(A.date) = 2016 
GROUP  BY A.id, 
          A.accnt, 
          A.amount