Question

I’m desperate with this query. I have two tables table1 and table2, tables are identical but they have different data. I’m trying to remove duplicities by columns code and manufacturer. To do that I need in final result ID from table1 ID from table2 and also columns code and manufacturer

 SELECT * FROM ( 
      SELECT id,code,manufacturer FROM table1 WHERE manufacturer = 1 
      UNION SELECT id,code,manufacturer FROM table2 WHERE manufacturer = 1
 ) AS t GROUP BY code HAVING COUNT(*) > 1

But in result i got only values from table1. It’s OK but I just need to get there id from table2 too. Please can anyone give me some tips how to do this ?

Answer 1

You have two basic problems:

Problem 1:
You are using UNION when you should be using UNION ALL, because UNION removes duplicates!

Problem 2:
This isn’t the right way to go about the problem. You should be using a simple join, not a union.
Try this:

 SELECT
     t1.id as table1_id,
     t2.id as table2_id,
     t1.code,
     t1.manufacturer
 FROM table1 t1
 JOIN table2 t2 
     ON t2.code = t1.code
     AND t2.manufacturer = t1.manufacturer
 WHERE manufacturer = 1 -- this WHERE clause is optional

Your use of the WHERE clause is a little odd – consider removing it to get all duplicates from all manufacturers.