SQL query and if statement

In my where statement I need to check two areas, if the first isn't populated, check the other.

if a.C_EFF_DT is NOT NULL then a.C_EFF_DT < date(current date - 6 months)
if a.C_EFF_DT is NULL then b.C_EFF_DT < date(current date - 6 months)

So basically if the first C_EFF_DT is null then check the second C_EFF_DT, if it has a date, then check it and don't worry about the second date.
Lee R Liddick JrReporting AnalystAsked:
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plusone3055Commented:
<cfif a.C_EFF_DT is NOT NULL>
 a.C_EFF_DT < date(current date - 6 months)
<cfelse>
 a.C_EFF_DT is NULL then b.C_EFF_DT < date(current date - 6 months)
</cfif>
0
David KrollCommented:
case
  when a.C_EFF_DT is NOT NULL then a.C_EFF_DT < date(current date - 6 months)
  when a.C_EFF_DT is NULL then b.C_EFF_DT < date(current date - 6 months)
  else (a date if the above two are false)
end
0
Lee R Liddick JrReporting AnalystAuthor Commented:
I didn't want this in CF...I am doing this in SAS SQL.  The case end in the where statement didn't work.  It doesn't like the less than sign...the query gives an error in the log.
0
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Lee R Liddick JrReporting AnalystAuthor Commented:
I figured it out myself, not even using 'if' or 'case' statements:
(
     a.c_eff_dt is NOT NULL
          AND a.c_eff_dt < date(current date - 6 months)
OR
     a.c_eff_dt is NULL
          AND b.c_eff_dt < date(current date - 6 months)
)
0
Lee R Liddick JrReporting AnalystAuthor Commented:
I've requested that this question be closed as follows:

Accepted answer: 0 points for leerljr68's comment #a39901107

for the following reason:

Accepting own comment since I figured it out myself with no assistance from the other expert comments.  Thank you.
0
_agx_Commented:
FYI, always wrap statements that mix AND/OR in parenthesis. Otherwise you're leaving the order of evaluation up to the db, which may or may not be what you want:

(
     <!--- first condition --->
     ( a.c_eff_dt is NOT NULL AND a.c_eff_dt < date(current date - 6 months)  )
OR
     ( a.c_eff_dt is NULL AND b.c_eff_dt < date(current date - 6 months)  )
)
0

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Lee R Liddick JrReporting AnalystAuthor Commented:
I'm awarding points to those who responded.
0
Lee R Liddick JrReporting AnalystAuthor Commented:
Even though I answered my own question, I'm awarding points for taking the time to respond.  Thank you all.
0
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