选择0个值作为现有列名

Question

嗨，我有2个表，每列3列：

位置

ID | KnownLocationID | Other 1 | 2 | Test 2 | 0 | TestOther

已知位置

ID | Title 1 | KNOWNTest 2 | KNOWNTestOther

我需要提取所有已知位置。如果为0，我需要拉Other

因此，第一个表的预期输出应该带回：

ID | Location 1 | KNOWNTestOther 2 | TestOther

预期产量

Answer 1

由于您没有标记询问的SQL，所以我假设它是MySQL。因此，您只需使用IF函数：

SELECT l.id, IF(l.KnownLocationID = 0, l.Other, kl.Title)
FROM Locations AS l
LEFT JOIN KnownLocations AS kl ON kl.ID = l.KnownLocationID

Working Fiddle

Answer 2

您只需使用CASE

SELECT l.id,
CASE WHEN l.KnownLocationID = 0 THEN l.other ELSE kl.Title END AS Location
FROM Locations AS l
LEFT JOIN KnownLocations AS kl ON kl.ID = l.KnownLocationID

Answer 3

查询：

SELECT loc.ID, IF(kl.Title IS NULL,loc.Other,kl.Title) AS Location FROM locations loc LEFT JOIN knownlocations kl ON kl.ID = loc. KnownLocationID