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MS SQL Multi Joins Update/Select

Posted on 2015-01-16
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Last Modified: 2015-01-18
Hi,
I have 3 tables structured as follows
table1 (equipnum, field1, field2)  (this table is used for reporting
table2 (projectID, equipnum, field11, field21)
table3 (projectID, equipnum, field111, field211)

I want to update table1 with values from table2 and table3
The join key table1-table2 : equipnum, table2-table3: projectID, equipnum

Regards
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Question by:Omer-Pitou
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3 Comments
 
LVL 143

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 40554884
0
 
LVL 15

Expert Comment

by:Vikas Garg
ID: 40554924
Hello,

You can try something like this

UPDATE Table1
SET Col2 = t2.Col2,
Col3 = t2.Col3
FROM Table1 t1
INNER JOIN Table2 t2 ON t1.Col1 = t2.Col1
WHERE t1.Col1 IN (21, 31)
GO

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LVL 14

Accepted Solution

by:
Nakul Vachhrajani earned 2000 total points
ID: 40556436
@Vikas: Your solution will work, only catch is that using UPDATE Table1.... FROM Table1 t1 may cause the table to block itself in an environment that supports parallelism. A better alternate is to use UPDATE t1....FROM Table1 t1 as shown below:

UPDATE t1
SET t1.field1 = t2.field11 - field111,
    t1.field2 = t2.field21 - field211
FROM dbo.table1 AS t1
INNER JOIN dbo.table2 AS t2 ON t1.equipnum = t2.equipnum
INNER JOIN dbo.table3 AS t3 ON t2.projectID = t3.projectID
                           AND t2.equipnum = t3.equipnum;

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