How to combine multiple rows into one in SQL?

Question

I have a particular table which has the following columns -

The Attribute ID can have 6 possible values from 1-6. This table will contain entries for all customers. Each row for a customer contains entry for 1-6 values.

Now What I would want to achieve is as follows -

I execute the following query -

SELECT CUST_ID,
        CASE WHEN "ATTR ID"=1 THEN "ATTR_VALUE" END AS ATTR_ID_1,
        CASE WHEN "ATTR ID"=2 THEN "ATTR_VALUE" END AS ATTR_ID_2,
        CASE WHEN "ATTR ID"=3 THEN "ATTR_VALUE" END AS ATTR_ID_3,
        CASE WHEN "ATTR ID"=4 THEN "ATTR_VALUE" END AS ATTR_ID_4,
        CASE WHEN "ATTR ID"=6 THEN "ATTR_VALUE" END AS ATTR_ID_5,
        CASE WHEN "ATTR ID"=7 THEN "ATTR_VALUE" END AS ATTR_ID_6

FROM "TABLE_NAME" where CUST_ID='20002123'

This produces the 6 columns fine but it ends up creating 3 rows as well -

Should I pivot the table ?

Thanks

Answer 1

You are quite close:

SELECT CUST_ID,
    max(CASE WHEN "ATTR ID"=1 THEN "ATTR_VALUE" END) AS ATTR_ID_1,
    max(CASE WHEN "ATTR ID"=2 THEN "ATTR_VALUE" END) AS ATTR_ID_2,
    max(CASE WHEN "ATTR ID"=3 THEN "ATTR_VALUE" END) AS ATTR_ID_3,
    max(CASE WHEN "ATTR ID"=4 THEN "ATTR_VALUE" END) AS ATTR_ID_4,
    max(CASE WHEN "ATTR ID"=6 THEN "ATTR_VALUE" END) AS ATTR_ID_5,
    max(CASE WHEN "ATTR ID"=7 THEN "ATTR_VALUE" END) AS ATTR_ID_6

FROM "TABLE_NAME" where CUST_ID='20002123'
Group by cust_id;

Also, you can look at pivot.

Answer 2

You can aggregate using GROUP BY CUST_ID to get the multiple rows as single row.

Try changing your query like following.

SELECT CUST_ID, 
       Max(ATTR_ID_1) AS ATTR_ID_1, 
       Max(ATTR_ID_2) AS ATTR_ID_2, 
       Max(ATTR_ID_3) AS ATTR_ID_3, 
       Max(ATTR_ID_4) AS ATTR_ID_4, 
       Max(ATTR_ID_5) AS ATTR_ID_5, 
       Max(ATTR_ID_6) AS ATTR_ID_6 
FROM   (SELECT CUST_ID, 
               CASE WHEN "ATTR ID" = 1 THEN "ATTR_VALUE"  END AS ATTR_ID_1, 
               CASE WHEN "ATTR ID" = 2 THEN "ATTR_VALUE"  END AS ATTR_ID_2, 
               CASE WHEN "ATTR ID" = 3 THEN "ATTR_VALUE"  END AS ATTR_ID_3, 
               CASE WHEN "ATTR ID" = 4 THEN "ATTR_VALUE"  END AS ATTR_ID_4, 
               CASE WHEN "ATTR ID" = 6 THEN "ATTR_VALUE"  END AS ATTR_ID_5, 
               CASE WHEN "ATTR ID" = 7 THEN "ATTR_VALUE"  END AS ATTR_ID_6 
        FROM   "TABLE_NAME" 
        WHERE  CUST_ID = '20002123')T 
GROUP  BY CUST_ID