Question

我甚至不知道我的问题叫什么名字，所以我只想提供一些样本数据。我不介意模糊的结果（这是我能想到表达它的最佳方式。我不介意我忽略一些数据，这是为了近似的评估，而不是详细的会计，如果这是有道理的）。但我确实需要表1中的每条记录，我想避免下面指出的空值。

这是可能的吗？

TABLE 1
acctnum sub fname  lname  phone
 12345   1   john   doe   xxx-xxx-xxxx
 12346   0   jane   doe   xxx-xxx-xxxx
 12347   0   rob    roy   xxx-xxx-xxxx
 12348   0   paul  smith  xxx-xxx-xxxx

TABLE 2
acctnum sub division
 12345   1   EAST
 12345   2   WEST
 12345   3   NORTH
 12346   1   TOP
 12346   2   BOTTOM
 12347   2   BALLOON
 12348   1   NORTH

因此，如果我们进行“常规外部”连接，我们会得到一些这样的结果，因为子0与第二个表不匹配：

TABLE AFTER JOIN
acctnum sub fname  lname  phone         division
 12345   1   john   doe   xxx-xxx-xxxx   EAST
 12346   0   jane   doe   xxx-xxx-xxxx   null
 12347   0   rob    roy   xxx-xxx-xxxx   null
 12348   0   paul  smith  xxx-xxx-xxxx   null

但我宁愿得到

TABLE AFTER JOIN
acctnum sub fname  lname  phone         division
 12345   1   john   doe   xxx-xxx-xxxx   EAST
 12346   0   jane   doe   xxx-xxx-xxxx   TOP
 12347   0   rob    roy   xxx-xxx-xxxx   BALLOON
 12348   0   paul  smith  xxx-xxx-xxxx   NORTH

我正试图避免：

TABLE AFTER JOIN
acctnum sub fname  lname  phone         division
 12345   1   john   doe   xxx-xxx-xxxx   EAST
 12345   1   john   doe   xxx-xxx-xxxx   WEST
 12345   1   john   doe   xxx-xxx-xxxx   NORTH
 12346   0   jane   doe   xxx-xxx-xxxx   TOP
 12346   0   jane   doe   xxx-xxx-xxxx   BOTTOM
 12347   0   rob    roy   xxx-xxx-xxxx   BALOON
 12348   0   paul  smith  xxx-xxx-xxxx   NORTH

所以我决定使用工会和两个if条件。对于表1中定义的子帐户但在表2中没有定义的情况，我会接受null，对于其他所有情况，我只会匹配min。

Answer 1

如果我理解正确，看起来您正试图加入sub列，如果匹配的话。如果sub上没有匹配项，那么您希望它为acctnum选择“第一”行。这是对的吗？

如果是这样，您需要在完全匹配时离开联接，然后在select语句上执行另一个左连接，该语句确定与最低division值对应的sub那个acctnum。 row_number()函数可以帮助您完成此操作，如下所示：

select
    t1.acctnum, 
    t1.sub, 
    t1.fname, 
    t1.lname, 
    t1.phone, 
    isnull(t2_match.division, t2_first.division) as division

from table1 t1

left join table2 t2_match on t2_match.acctnum = t1.acctnum and t2_match.sub = t1.sub
left join 
(
    select 
        acctnum, 
        sub, 
        division,
        row_number() over (partition by acctnum order by sub) as rownum

    from table2
) t2_first on t2_first.acctnum = t1.acctnum

修改

如果您根本不关心哪个记录，当匹配的sub不存在时从表2中返回，您可以组合两个不同的查询（一个匹配sub和一个只需要使用union进行最小或最大分割。

select t1.acctnum, t1.sub, t1.fname, t1.lname, t1.phone, t2.division from table1 t1 join table2 t2 on t2.acctnum = t1.acctnum and t2.sub = t1.sub union select t1.acctnum, t1.sub, t1.fname, t1.lname, t1.phone, min(t2.division) from table1 t1 join table2 t2 on t2.acctnum = t1.acctnum left join table2 t2_match on t2_match.acctnum = t1.acctnum and t2_match.sub = t1.sub where t2_match.acctnum is null

就个人而言，我没有发现union语法更加引人注目，您现在必须在两个地方维护查询。出于这个原因，我赞成row_number()方法。

Answer 2

尝试使用

SELECT     MIN(Table_1.acctnum) as acctnum , MIN(Table_1.sub) as sub,MIN( Table_1.fname) as fname, MIN(Table_1.lname) as name, MIN(Table_1.phone) as phone, MIN(Table_2.division) as division 
FROM Table_1 INNER JOIN   Table_2 ON Table_1.acctnum = Table_2.acctnum AND Table_1.sub = Table_2.sub
where Table_1.sub>0
group by Table_1.acctnum 
union 
SELECT     MIN(Table_1.acctnum) as acctnum , MIN(Table_1.sub) as sub,MIN( Table_1.fname) as fname, MIN(Table_1.lname) as name, MIN(Table_1.phone) as phone, MIN(Table_2.division) as division 
FROM Table_1 INNER JOIN   Table_2 ON Table_1.acctnum = Table_2.acctnum 
where Table_1.sub=0
group by Table_1.acctnum

这是结果

12345   1   john        doe         xxxxxxxxxx  EAST      
12346   0   jane        doe         xxxxxxxxxx  BOTTOM    
12347   0   rob         roy         xxxxxxxxxx  BALLOON   
12348   0   paul        smith       xxxxxxxxxx  NORTH

如果你将min改为max，那么第二行将会出现BOTTOM

Answer 3

这将准确地给出您想要的结果（对于显示的数据）：

已更新以假设始终存在sub == 1值：

SELECT
    T1.acctnum,
    T1.sub,
    T1.fname,
    T1.lname,
    T1.phone,
    T2.division
FROM
    TABLE_1 T1
LEFT JOIN
    TABLE_2 T2  ON T1.acctnum = T2.acctnum
AND
    T2.sub  = (SELECT MIN(T3.sub) FROM TABLE_2 T3  WHERE T1.acctnum = T3.acctnum)
ORDER BY
    T1.lname,
    T1.fname,
    T1.acctnum

Answer 4

它也可能对您有用：

SELECT  t1.acctnum, t1.sub, t1.fname, t1.lname, t1.phone, 
ISNULL(MAX(t2.division),MAX(t3.division)) as division
FROM table_1 t1
LEFT JOIN table_2 t2 ON (t2.acctnum = t1.acctnum AND t1.sub = t2.sub)
LEFT JOIN table_2 t3 ON (t3.acctnum = t1.acctnum)
GROUP BY  t1.acctnum, t1.sub, t1.fname, t1.lname, t1.phone

SQL Join忽略多个匹配（模糊结果ok）

这是可能的吗？

4 个答案: