Question

I want to perform update operation by joining two different tables.

My tables are :

dim_sess

name                                        role
20111012133513aaa123                    
20110908072611aaa121        
20111002210235bbb853
20120113113353bbbl971           

The role column is updated later.

and the other table is

employeerole
username           role             thedate
aaa         technician      2011-10-12 13:35:13
aaa         technician      2011-09-08 07:26:11
bbb         day guard       2011-10-02 21:02:35
bbb         day guard       2012-01-13 11:33:53
bbb         night guard     2012-01-13 21:30:00

I want to update role in the dim_sess table depending upon username and startdate. The same user can have different role in different date. There is no common column in two table and the only column to perform join is “name” in dim_sess.

I write the following query to update the dim_ses table.

 UPDATE dim_sess
SET role = (SELECT employeerole.role FROM employeerole
WHERE SUBSTRING(dim_sess.name,15,7) = employeerole.username
AND SUBSTRING(dim_sess.name,1,14) = (TEXTCAT( TEXTCAT(TEXTCAT(SUBSTRING(thedate,1,4), SUBSTRING(thedate,6,2)) , TEXTCAT(SUBSTRING(thedate,9,2), SUBSTRING(thedate,12,2)) ), TEXTCAT(      SUBSTRING(thedate,15,2), SUBSTRING(thedate,18,2)))))
WHERE SUBSTRING(dim_sess.name,1,21) = (SELECT TEXTCAT((TEXTCAT(TEXTCAT(TEXTCAT(SUBSTRING(thedate,1,4), SUBSTRING(thedate,6,2)) , TEXTCAT(SUBSTRING(thedate,9,2), SUBSTRING(thedate,12,2))), TEXTCAT(SUBSTRING(thedate,15,2), SUBSTRING(thedate,18,2)))) , employeerole.username) AS session FROM employeerole);

The error message I get is:
ERROR:  more than one row returned by a subquery used as an expression

Since there is no common column between two tables, I try to join them by using the substring function to match the results. But this seems to be a bad solution. I was wondering if there is other way to join these two tables.

Answer 1

Try this:

update DIM_SESS DS
   set ROLE =
         (select ER.ROLE
            from EMPLOYEEROLE ER
           where substr(
                   DS.NAME
                  ,1
                  ,length(to_char(STARTDATE, 'yyyymmddhh24miss') || USERNAME)) like
                   to_char(STARTDATE, 'yyyymmddhh24miss') || USERNAME);

I’ve tested this in Oracle but I think you might be using PostgreSQL so the syntax might be a little different.