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Posted on 2001-08-10
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Last Modified: 2007-11-27
Hi,
I have two tables and I want to update a field of want table based on the presence of the ID's in the other table.

For example:

Table A has the following records:

col1 col2
ID1  someData
ID2  someData
ID3  someData

Table B has the following records:

col1 col2
ID0  NULL
ID1  NULL
ID2  NULL
ID3  NULL
ID4  NULL

I want to update col2 in table B with 'Y' based on the occurence of the ID's in table A.  In this case, col2 of ID1,ID2, and ID3 in table B should be marked with 'Y' after the update.

How do I do this with a single SQL update statement?

Thanks.
Gamestors
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Comment
Question by:gamestors
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10 Comments
 
LVL 143

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 6372656
Ths syntax may vary from the Database you are using:
MSSQL Server's Version:

UPDATE TableB
SET col2 = 'Y'
FROM TableB
JOIN TableA
ON TableA.col1 = TableB.col1

Cheers
0
 
LVL 18

Expert Comment

by:nigelrivett
ID: 6372849
That's an sql server extension
I think this is ansi standard sql (could be wrong though).


update TableB
set col2 = 'Y'
where exists (select * from TableA where TableA.col1 = TableB.col1)

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Author Comment

by:gamestors
ID: 6373178
I should have mentioned that I use MySql.
I tried both but neither one worked.

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Expert Comment

by:Elainec
ID: 6374640
gamestors
Try:

UPDATE tableB
set col2 = 'Y'
where col1 in (select col1 from tableA);

And yet another way may be:

UPDATE tableB INNER JOIN tableA
ON tableA.col1 = tableB.col1
SET tableB.col2 = 'Y';

A useful link for mySQL is www.mysql.com

Hope that helps & have fun!
Elaine
0
 

Expert Comment

by:dataliberator
ID: 6374649
not sure about mysql..... but you can use cursors I imagine?

DECLARE
--declaration of cursor, selects column1 values  from tablea, where ids match in tables
  CURSOR c1 IS
    SELECT b.column1
        FROM tablea a,
                    tableb b
    WHERE a.column1 = b.column1

-- creates a variable of same type of values selected in the cursor above (just 1 here, but could be many
--  columns)
   c1_rec c1%ROWTYPE;
 
BEGIN
-- this opend the cursor, and loops through it until there is no more data returned from the cursor
-- same as using OPEN c1; FETCH c1 INTO c1_rec, EXIT WHEN c1%NOTFOUND
-- but shorter obviously.......... - works in Oracle anyway
   FOR c1_rec IN c1 LOOP

       UPDATE TableB
               SET TableB. column2 = 'Y'
        WHERE TableB.column1 = c1_rec.column1;

       COMMIT;

  END LOOP

END;


-- Hope that helps..... and these lines are comments by the way.........
-- ~ Liberator
0
 

Author Comment

by:gamestors
ID: 6379871
Elainec,

According to the documentation on mysql.com, keywords 'IN', 'NOT IN',and 'NOT EXISTS' are not yet implemented in MySql.

Thanks anyway,

0
 

Accepted Solution

by:
Elainec earned 400 total points
ID: 6380069
Yes, but did you try the code:

UPDATE tableB INNER JOIN tableA
ON tableA.col1 = tableB.col1
SET tableB.col2 = 'Y';

??
I extracted this directly out of the mysql web site!
Elaine :-)
0
 

Author Comment

by:gamestors
ID: 6461670
I was looking for a simple way to do the update.  Your approach is too complicated. Thanks anyway.
0
 
LVL 143

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 6463088
i do not agree with the grade C you gave, gamestors.
i asked CS to correct this, because the approach isn't complicated at all, it is the way it works in SQL Server.
http://www.experts-exchange.com/jsp/qManageQuestion.jsp?ta=commspt&qid=20179769
Regards
0
 

Expert Comment

by:ComTech
ID: 6463243
I agree with the grade change.  We are currently changing our grading system, and any comment that leads to an answer deserves an A.

Thanks,
ComTech
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