1

I have the following Problem: I have a table table1 with multiple columns col1 through col2:

+------+------+  
| col1 | col2 |    
+------+------+  
|  1   |  4   |  
|  2   |  4   |  
|  3   |  4   |  
|  4   |  5   |  
+------+------+

Now I need all entries col1-entries with a four in in col2, for which I use: 

SELECT @col2fours := col1 FROM table1 WHERE col2 = 4;

Now I have a table2 where I want to set the rows where col3 has one of the values stored in @col2fours. For this I use:

SELECT * ID FROM table2 WHERE col3 IN @col2fours;

This doesn't work. I already tried = and having instead of in as well as using Group_concat. Nothing worked for me so far.
I would like to do this directly in mySQL because the database lies on a server and I want to reduce accesses to the database as much as possible. The real problem has somewhat more tables involved than 2 ;). Appreciate any input, thanks.

Max Belli
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2 Answers2

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you can use sub query like this directly 

SELECT * FROM table2 WHERE col3 IN (SELECT col1 FROM table1 WHERE col2 = 4);
krishn Patel
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1

This approach is a no-go, since in MySQL there is no array data type, so a variable can hold only 1 value at a time.

Just use a subquery or join to achieve the expected results:

SELECT * FROM table2 WHERE col3 IN (SELECT col1 FROM table1 WHERE col2 = 4)

SELECT table2.* FROM table2
INNER JOIN table1 ON table2.col3=table1.col1
WHERE table1.col2 = 4
Shadow
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  • Thanks! I think the subquery is the way to go for me, the join seems a bit inappropriate for my problem, but thanks for your help! – Max Belli May 24 '17 at 06:19