Use of MIN with text data

Question

I am not familiar with using MIN with text data as in the sample below and could use some help in deciphering what it is doing. This SELECT statement is taken from a larger CREATE OR REPLACE VIEW statement. The first line of the WHERE clause is making the connection to look at the correct user's information. The section after the first AND is what I am trying to interpret correctly. I have moved into a new position and wasn't around when this view was created. The statement is designed to assign the correct DOMAIN_ID to each user based on values in the elms.elms_dom_lkup table ed. This table consists of 4 columns: DOMAIN_ID, PROC_LVL, LOCATION, AND POSITION. The DOMAIN_ID is the only field that is not nullable. The primary key for the table is a combination of the 4 columns. The section after the first AND matches the PROC_LVL from the ed (lookup table) to the PROCESS_LEVEL in the cd (reference table) and confirms the process level is associated with the users primary position. It then looks for one of three conditions:
1. process levels match and LOCATION and POSITION are NULL
2. process levels match and LOCATION matches user's location in a reference table
3. PROC_LVL is NULL and POSITION matches user's position in a reference table
(SELECT MIN (domain_id)
FROM elms.elms_dom_lkup ed, mici.const_dept cd
WHERE c.constituent_id = cd.constituent_id
AND ( (ed.proc_lvl = cd.process_level AND cd.pos_level = 1
AND ( (ed.location IS NULL AND ed.position IS NULL)
OR (LOWER (ed.location) = LOWER (loc.campus))))
OR (LOWER (ed.position) = LOWER (c.job_desc)
AND ed.proc_lvl IS NULL))), /*Domain ID*/
My question revolves around the priority on those matches. The ed table is not organized in any manor. The records are in the order they were entered. Does the MIN in the SELECT statement cause the DOMAIN_ID

Answer 1

Hi,
Welcome to the forum!
If v is a string column (such as a VARCHAR2), then MIN (v) is the first string in collating order (that is, alphabetic order, but with numbers and punctuation symols given particular values in the ordering).
It lookw like the code fragment you posted is a Scalar Sub-Query , that is, a sub-query used where an expression is exprected. For example, in a query like this:
SELECT  *
FROM    scott.emp
WHERE   sal     > 1200
;You can replace the literal 1200 with any kind of numeric expression, even
SELECT  *
FROM    scott.emp
WHERE   sal     > (     --Begin scalar sub-query
                SELECT  AVG (sal)
                FROM    scott.emp
            )     -- End scalar sub-query
;You have to be careful that a sclar sub-query produces exactly one column, and either 0 or 1 rows. You'll get a run-time error if the sub-query ever produces 2 or more rows.
People sometimes use MIN in situations like yours when the sub-query might otherwise return 2 or more rows, and either:
(a) all the non-NULL rows will contain the same domain_id, or
(b) it doesn't matter which domain_id is used, just so long as it is one that actually exists in the result set.
842436 wrote:
My question revolves around the priority on those matches. The ed table is not organized in any manor. The records are in the order they were entered. Does the MIN in the SELECT statement cause the DOMAIN_IDSorry, I don't understand exactly what you're asking.
Rows in a relational table are never in any intrensic order.
It looks like the question got cut off. Does the MIN in the SELECT statement cause the DOMAIN_ID to do what?
Edited by: Frank Kulash on Mar 7, 2011 3:01 PM
I see you corrected your first post.
842436 wrote:
... My question is does the MIN in the SELECT statement cause the DOMAIN_ID from the first record that meets any of the 3 conditions to be returned?Yes, it makes the sub-0query return the first domain_id ( in alphabetic order ) that meets all the conditions. If there are 1,000 rows that meet all the conditions, the query will ind all 1,000 of them, keeping track iof which one is first in alphabetic order. Remember that
'127.255.255.0' is less than
'25.0.0.0' in alphabetic order, because '1' is less that '2'.