Get value by looping through table column

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Get value by looping through table column

Author

Topic

kme
Starting Member

1 Post

Posted - 2014-04-05 : 16:54:30

Hello,

Here are two tables:

TABLE_A
[ac] [dest]
1 A
1
1
2
2
3
3 B
3

(ac=1, dest=A; ac=3, dest=B)
The space between '1' and 'A' isn't showing up correctly.

TABLE_B
[fleet] [ron]
1 A
1 A
1 A
1 A
1 A
2
2
2
2
3 B
3 B

(fleet=1, ron=A; fleet=3, ron=B; etc.etc.)

I would like to fill TABLE_B's column "ron" by referring to TABLE_A's column "dest".
ac = fleet, and for each ac, I would like to loop through the 'dest' column in TABLE_A from top to bottom to get the top most value. If there are no values (like with ac = 2), then value is blank.
For 1, the value is A.
For 2, the value is blank.
For 3, the value is B.

Therefore, in TABLE_B, for all 'ron' for fleet=1, the value is filled A.
For all 'ron' for fleet=2, the value is blank.
For all 'ron' for fleet=3, the value is B.

How do you code this?

- create variable 'v'
- where ac=fleet, loop through 'dest' from top to bottom to get top-most value. variable 'v' = the value.
- in TABLE_B, for each ac=fleet, insert variable 'v' into the 'ron' column

Thanks so much, I would appreciate any help.

visakh16
Very Important crosS Applying yaK Herder

52326 Posts

Posted - 2014-04-13 : 14:49:53

looks like this to me


UPDATE b
SET ron = a.dest
FROM tableB b
INNER JOIN (SELECT ac,MAX(dest) AS dest
            FROM tableA
            GROUP BY ac)a
ON a.ac = b.fleet

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