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

I have three tables from three different databases. I have to retrieve multiple columns from these three tables, which I did by using inner join. Now I have to retrieve only that row that is recently updated ie the last row. How do I retrieve the last row along with multiple columns from different databases?

My sql query is

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

You can use TOP 1 with ORDER BY

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

If you can't use TOP1, and logtime, to order by DESC, like the other post suggests, You can try this...

It gets the entire result set into a temp table with an identity column, and then selects the max identity from that table.

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)

But in my opinion, the TOP 1 ORDER BY DESC, approach is the way to go.