sql - 如何让SQL INNER JOIN接受空结果

我有以下查询:

SELECT TOP 25 CLIENT_ID_MD5, COUNT(CLIENT_ID_MD5) TOTAL
FROM dbo.amazonlogs
GROUP BY CLIENT_ID_MD5
ORDER BY COUNT(*) DESC;

哪个返回:

283fe255cbc25c804eb0c05f84ee5d52    864458
879100cf8aa8b993a8c53f0137a3a176    126122
06c181de7f35ee039fec84579e82883d    88719
69ffb6c6fd5f52de0d5535ce56286671    68863
703441aa63c0ac1f39fe9e4a4cc8239a    47434
3fd023e7b2047e78c6742e2fc5b66fce    45350
a8b72ca65ba2440e8e4028a832ec2160    39524
...

我想使用从此查询返回的MD5检索相应的客户端名称(FIRM)，所以行可能看起来像:

879100cf8aa8b993a8c53f0137a3a176    126122    Burger King

所以我做了这个查询:

SELECT a.CLIENT_ID_MD5, COUNT(a.CLIENT_ID_MD5) TOTAL, c.FIRM
FROM dbo.amazonlogs a
  INNER JOIN dbo.customers c
    ON c.CLIENT_ID_MD5 = a.CLIENT_ID_MD5
GROUP BY a.CLIENT_ID_MD5, c.FIRM
ORDER BY COUNT(*) DESC;

这将返回类似:

879100cf8aa8b993a8c53f0137a3a176    126122    Burger King
06c181de7f35ee039fec84579e82883d    88719     McDonalds
703441aa63c0ac1f39fe9e4a4cc8239a    47434     Wendy's
3fd023e7b2047e78c6742e2fc5b66fce    45350     Tim Horton's

可行，除了如果给定MD5没有对应的FIRM，我需要为c.FIRM返回一个空值。例如:

879100cf8aa8b993a8c53f0137a3a176    126122    Burger King
06c181de7f35ee039fec84579e82883d    88719     McDonalds
69ffb6c6fd5f52de0d5535ce56286671    68863
703441aa63c0ac1f39fe9e4a4cc8239a    47434     Wendy's
3fd023e7b2047e78c6742e2fc5b66fce    45350     Tim Horton's

即使没有对应的c.FIRM，我该如何修改查询以仍然返回行？

最佳答案

用INNER JOIN替换LEFT JOIN

Firm

sql - 如何让SQL INNER JOIN接受空结果