Using decode to define "where" clause

Question

Gurus,
Before, I was unioning several queries to get my desired results. Is there a way to utilize decode to define my "where" conditions?
Thanks
msi.global_attribute1               HTS_Number,           
msi.global_attribute2               ECCN_Number  ,
msi.market_price                    price,     --- double-check
decode(msi.serial_number_control_code,5,'Serial','Lot') control_type,
-- add item_type
--Item Label Creation        At Receipt or At Sales Order Issue
(case
when enabled_flag = 'Y' and end_date_active is null then 'Active'
when enabled_flag = 'Y' and end_date_active > sysdate then 'Active'
when enabled_flag = 'Y' and end_date_active < sysdate then 'Inactive'
when enabled_flag = 'N' then 'Inactive'
else 'Active'
end) status,
from inv.mtl_system_items_b   msi,
     po_hazard_classes    phc,
    po_un_numbers        pun
where msi.hazard_class_id = phc.hazard_class_id(+)  
and   msi.un_number_id = pun.un_number_id(+)   
and   msi.organization_id = 543
and   msi.creation_date = msi.last_update_date
--and   'New Items' = nvl(p_item_status,'All Items') --p_item_status
and   decode('New Items', --p_item_status,
      'New Items', (msi.creation_date = msi.last_update_date),
      'Updated Items', (msi.creation_date <> msi.last_update_date),
      'All Items', (1=1), (1=1))
  and msi.segment2 = '14078'

Answer 1

Hi,
sreese wrote:
Before, I was unioning several queries to get my desired results. Is there a way to utilize decode to define my "where" conditions?Depending on what you mean, yes.
Whenever you have a problem, please post a little sample data (CREATE TABLE and INSERT statements, relevant columns only) from all tables involved.
Also post the results you want from that data, and an explanation of how you get those results from that data, with specific examples.
Simplify the problem as much as possible. Remove all tables and columns that play no role in this problem.
Always say which version of Oracle you're using.
Here's an example of two UNIONed queries:
SELECT       deptno
,       SUM (sal)     AS total_sal
,       'MANAGEMENT'     AS grp_name
FROM       scott.emp
WHERE       job     IN ('MANAGER', 'PRESIDENT')
GROUP BY  deptno
     UNION ALL
SELECT       deptno
,       SUM (sal)     AS total_sal
,       'OLD-TIMERS'     AS grp_name
FROM       scott.emp
WHERE       hiredate     < DATE '1984-01-01'
GROUP BY  deptno
ORDER BY  deptno
,            grp_name
;Output:
`   DEPTNO  TOTAL_SAL GRP_NAME
        10       7450 MANAGEMENT
        10       8750 OLD-TIMERS
        20       2975 MANAGEMENT
        20       6775 OLD-TIMERS
        30       2850 MANAGEMENT
        30       9400 OLD-TIMERSA more efficient way to get the same information, without a UNION is:
SELECT       deptno
,       SUM (CASE WHEN job IN ('MANAGER', 'PRESIDENT') THEN sal END)     AS management
,       SUM (CASE WHEN hiredate < DATE '1984-01-01'      THEN sal END)     AS old_timers
FROM       scott.emp
WHERE       job          IN ('MANAGER', 'PRESIDENT')
OR       hiredate     < DATE '1984-01-01'
GROUP BY  deptno
ORDER BY  deptno
;Output:
`   DEPTNO MANAGEMENT OLD_TIMERS
        10       7450       8750
        20       2975       6775
        30       2850       9400As you can see, the results aren't exactly the same. UNION makes it easy to get more rows in the output than there are in the original; CASE (or DECODE,you can use whichever you like) makes it easy to get fewer rows and more columns. If you reallt want one kind of output or the other, it can be done with a little more work using either UNION or CASE.
When using CASE, the WHERE clause is typically more inclusive than any of the WHERE caluses in the UNION. Some of the conditions (in this example, all of the conditions) that were in the separate WHERE clauses of the UNION get changed to be conditions in separate CASE expressions.