Help: Group By condition

Question

Hello folks am actually trying to figure whether we can use the following condition i.e "to_char(sysdate, 'FMMon YYYY')," in the group by clause, Or can we use the alias "Period" instead,Can anyone please throw some light on this.
SELECT Client. Client Name,
"CUBS SNAPSHOT". HMG Flag,
select TRUNC (SYSDATE, 'MONTH') - 1 from dual AS PeriodThruDate,
select to_char(sysdate, 'FMMon YYYY') from dual AS Period
FROM "CUBS SNAPSHOT", Client
GROUP BY Client. Client Name,
"CUBS SNAPSHOT".CLIENT,
"CUBS SNAPSHOT".TYPE,
"CUBS SNAPSHOT".clipStatus,
"CUBS SNAPSHOT".SUBTYPE,
to_char(sysdate, 'FMMon YYYY'),
"CUBS SNAPSHOT". HMG Flag,
TRUNC (SYSDATE, 'MONTH') - 1
Thanks

Answer 1

Hi,
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SYSDATE is treated as a constant in GROUP BY queries.
You can have constants in the GROUP BY clause if you really want to, but there's no point. If you have a GROUP BY clause anyway, adding constants to it won't change the results.
You can't use a column alias in the GROUP BY clause of the same query where it was defined.
I think the following is syntactically correct:
SELECT    Client.Client          Name,
       "CUBS SNAPSHOT".HMG     Flag,
       ( select  TRUNC (SYSDATE, 'MONTH') - 1
         from       dual
       )               AS PeriodThruDate,
       ( select  to_char (sysdate, 'FMMon YYYY')
         from       dual
       )               AS Period
FROM        "CUBS SNAPSHOT",
       Client
GROUP BY  Client.Client,
             "CUBS SNAPSHOT".CLIENT,
       "CUBS SNAPSHOT".TYPE,
       "CUBS SNAPSHOT".clipStatus,
       "CUBS SNAPSHOT".SUBTYPE,
       to_char(sysdate, 'FMMon YYYY'),          -- Why?
       "CUBS SNAPSHOT".HMG,
       TRUNC (SYSDATE, 'MONTH') - 1               -- Why?
;Scalar-sub-queries (like PeriodThruDate and Period) must be enclosed in parentheses. You don't have to use a sub-query in these two cases. Instead of
( select  TRUNC (SYSDATE, 'MONTH') - 1
  from       dual
)                    AS PeriodThruDate,you could say:
TRUNC (SYSDATE, 'MONTH') - 1      AS PeriodThruDate,The query above is doing a cross-join betwee the two tables. That's not necessarily an error, but it almost certainly isn't what you want. Every table in the FROM clause is usually referenced in at least one join condition.
I suggest writing much smaller queries, and adding to them one or two lines at a time. You'll find it much easier to locate and fix mistakes that way.
That is, don't wite 14 lines of code and then try to run it.
Write maybe 2 lines. Test it, and make corrections as necessary.
When it does what it's supposed to dio perfectly, add another line or two and test again.