SQL queries for multiple columns depends on same column of another table

Question

5.00/5 (2 votes)

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See the following scenario:

Tables for the question:

SQL

Table : T1
c10  c12
---  ----
e1   A
e2   B
e3   C

Table: T2

c1  c2  c3  c4  c5   C6
--- -- --- ---  ---  ---
1   P  e1  e2   null  X
2   Q  e3  null null  Y
3   R  e2  e1   null  X
4   S  e3  e1   e2    Z


The c3, c4 and c5 columns of T2 table depends on c12 column of T1 table.

I want the following output:


c1  c2  c3  c4  c5
--- -- --- ---  ---
1   P   A   B   null
2   Q   C  null null
3   R   B   A   null
4   S   C   A   B

Can you help me to write an SQL to retrieve the above output from the table T1 and T2?

The SQL may be like:

SQL

Select c1, c2, t1.c12 as c3....... from t1, t2 where join condition

But I am not getting the actual sql in my mind.
So please help me regarding this.

Posted 19-Mar-12 4:48am

AhmedMasum

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ProEnggSoft 19-Mar-12 13:20pm

My 5! for nicely formulating the question.

1 solution

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ProEnggSoft · Accepted Answer · 2012-03-19T07:33:00

SQL

SELECT c1,c2,(SELECT TOP 1 c12 FROM T1 WHERE T1.c10=T2.c3) AS c3,
    (SELECT TOP 1 c12 FROM T1 WHERE T1.c10=T2.c4) AS c4,
    (SELECT TOP 1 c12 FROM T1 WHERE T1.c10=T2.c5) AS c5
FROM T2
-- If multiple values are expected in T1 table say
-- e1,A  e1,M  then ORDER BY clause can be used for greater
-- control on the value returned by sub query
SELECT c1,c2,(SELECT TOP 1 c12 FROM T1 WHERE T1.c10=T2.c3 ORDER BY T1.c12 DESC) AS c3,
    (SELECT TOP 1 c12 FROM T1 WHERE T1.c10=T2.c4 ORDER BY T1.c12) AS c4,
    (SELECT TOP 1 c12 FROM T1 WHERE T1.c10=T2.c5 ORDER BY T1.c10) AS c5
FROM T2