SQL查询以选择最后一行以及使用内部联接检索的其他列

Question

我有来自三个不同数据库的三个表。 我必须从这三个表中检索多个列，这是使用内部联接完成的。 现在，我只需要检索最近更新的那一行，即最后一行。 如何从不同的数据库检索最后一行以及多列？

我的SQL查询是

SELECT a.logtime, a.BL1_data_SS_ST, a.BL2_data_SS_ST, a.BL3_data_SS_ST, 
a.BL4_data_SS_ST, a.BL5_data_SS_ST, a.BL6_data_SS_ST, a.BL7_data_SS_ST, 
a.BL8_data_SS_ST, a.BL9_data_SS_ST, a.BL10_data_SS_ST, a.BL11_data_SS_ST,
a.BL12_data_SS_ST, a.BL13_data_SS_ST, a.BL14_data_SS_ST, a.BL15_data_SS_ST, 
a.BL16_data_SS_ST, a.BL17_data_SS_ST, a.BL18_data_SS_ST, a.BL19_data_SS_ST, 
a.BL20_data_SS_ST, a.BL21_data_SS_ST, a.BL22_data_SS_ST, a.BL23_data_SS_ST, 
a.BL24_data_SS_ST, a.BL25_data_SS_ST, a.BL26_data_SS_ST, a.BL27_data_SS_ST,
b.st1_prmt_status_p45, c.beam_current, c.beam_energy

FROM INDUS2_BLFE.dbo.main_BLFE_status a 
INNER JOIN INDUS2_MSIS.dbo.main_MSIS_status b on a.logtime = b.logtime 
INNER JOIN INDUS2_BDS.dbo.DCCT c on b.logtime = c.logtime ''

Answer 1

您可以将TOP 1与ORDER BY一起使用

SELECT TOP 1 a.logtime, a.BL1_data_SS_ST, a.BL2_data_SS_ST, a.BL3_data_SS_ST, 
a.BL4_data_SS_ST, a.BL5_data_SS_ST, a.BL6_data_SS_ST, a.BL7_data_SS_ST, 
a.BL8_data_SS_ST, a.BL9_data_SS_ST, a.BL10_data_SS_ST, a.BL11_data_SS_ST,
a.BL12_data_SS_ST, a.BL13_data_SS_ST, a.BL14_data_SS_ST, a.BL15_data_SS_ST,
a.BL16_data_SS_ST, a.BL17_data_SS_ST, a.BL18_data_SS_ST, a.BL19_data_SS_ST,
a.BL20_data_SS_ST, a.BL21_data_SS_ST, a.BL22_data_SS_ST, a.BL23_data_SS_ST, 
a.BL24_data_SS_ST, a.BL25_data_SS_ST, a.BL26_data_SS_ST, a.BL27_data_SS_ST,
b.st1_prmt_status_p45,c.beam_current, c.beam_energy
FROM INDUS2_BLFE.dbo.main_BLFE_status a 
INNER JOIN INDUS2_MSIS.dbo.main_MSIS_status b on a.logtime = b.logtime 
INNER JOIN INDUS2_BDS.dbo.DCCT c on b.logtime = c.logtime ''
ORDER BY a.logtime DESC

Answer 2

如果您不能使用TOP1和logtime来按DESC进行订购，就像其他帖子所建议的那样，您可以尝试一下...

它将整个结果集放入带有标识列的临时表中，然后从该表中选择最大标识。

SELECT IDENTITY(INT, 1, 1) Cnt, *
INTO #TMP 
SELECT a.logtime, a.BL1_data_SS_ST, a.BL2_data_SS_ST, a.BL3_data_SS_ST, 
a.BL4_data_SS_ST, a.BL5_data_SS_ST, a.BL6_data_SS_ST, a.BL7_data_SS_ST, 
a.BL8_data_SS_ST, a.BL9_data_SS_ST, a.BL10_data_SS_ST, a.BL11_data_SS_ST,
a.BL12_data_SS_ST, a.BL13_data_SS_ST, a.BL14_data_SS_ST, a.BL15_data_SS_ST,
a.BL16_data_SS_ST, a.BL17_data_SS_ST, a.BL18_data_SS_ST, a.BL19_data_SS_ST,
a.BL20_data_SS_ST, a.BL21_data_SS_ST, a.BL22_data_SS_ST, a.BL23_data_SS_ST,
a.BL24_data_SS_ST, a.BL25_data_SS_ST, a.BL26_data_SS_ST, a.BL27_data_SS_ST,
b.st1_prmt_status_p45, c.beam_current, c.beam_energy

FROM  INDUS2_BLFE.dbo.main_BLFE_status a 
INNER JOIN INDUS2_MSIS.dbo.main_MSIS_status b on a.logtime = b.logtime 
INNER JOIN INDUS2_BDS.dbo.DCCT c on b.logtime = c.logtime ''

SELECT *
FROM #TMP
WHERE Cnt = (SELECT MAX(Cnt) FROM #TMP)

但是我认为，按顺序进行的TOP 1 ORDER BY DECO是必经之路。