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MS SQL Query De-Mystified

Posted on 2009-07-13
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Last Modified: 2012-05-07
Can some one translate this query so it can be understood as to what it is doing?  Feel free to explain it as if you were talking to a Monkey or 3 year old


SELECT P.County_ID, P.Parcel_ID, P.Rate_ID, P.Add_ID, P.Exempt, IIf(P.UnitAssessment=-1,P.UnitAssessmentValue,IIf(P.BuildHT>=4,(P.CTaxLand*(P.Benef*0.01))+((P.CTaxBuild/P.BuildHT)*3*(P.Benef*0.01))+((P.CTaxBuild/P.BuildHT)*(P.BuildHT-3)*0.06),IIf(P.Partial_Prot=-1,IIf(P.Bldg_Incl=-1,(P.CTaxLand*(P.Wet_Perc*0.01)*0.03)+(P.CTaxBuild*0.03),P.CTaxLand*(P.Wet_Perc*0.01)*0.03),(P.CTaxLand+P.CTaxBuild)*(P.Benef*0.01)))) AS dblBenefit, BR.Bond_rate, TR.Tax_Rate, P.id, P.UnitAssessment, P.UnitAssessmentValue, TR.TaxRate_Description, P.MainCounty
FROM BondRate AS BR, MATCHEDTAXPARCELS AS P INNER JOIN TaxRate AS TR ON P.Rate_ID=TR.CharCode;
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Question by:Jason Jones
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2 Comments
 
LVL 15

Accepted Solution

by:
mohan_sekar earned 2000 total points
ID: 24841937
Pseudo code:

if p.UnitAssessment = -1 then
   dblBenefit = p.UnitAssessmentValue
else
   if (p.BuildHT >= 4) then
        dblBenefit = (P.CTaxLand*(P.Benef*0.01))+((P.CTaxBuild/P.BuildHT)*3*(P.Benef*0.01)) +
                        ((P.CTaxBuild/P.BuildHT)*(P.BuildHT-3)*0.06)
   else
       if P.Partial_Prot = -1 then
             if P.Bldg_Incl = -1 then
                   dblBenefit = (P.CTaxLand*(P.Wet_Perc*0.01)*0.03)+(P.CTaxBuild*0.03)
             else
                   dblBenefit = P.CTaxLand*(P.Wet_Perc*0.01)*0.03)
             end if
       else
             dblBenefit = (P.CTaxLand+P.CTaxBuild)*(P.Benef*0.01)
   end if
end if
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LVL 4

Expert Comment

by:j_s_kelley
ID: 24842301
The best way to understand a query is to actually format it.  Once I did that, I could see better.  Without understanding the exact nature of the query, the vast majority of it is straightforward.  It is a join where most of the fields are selected.  the field dblBenefit looks like it has some serious logic to determine it's value.  That would take an understanding of the domain to do it justice.  Also, one thing I did notice is that there are 3 tables but only two of them are joined.  BondRate is not joined with anything.  You have MatchedTaxParcels joined with Tax Rate and the result of that will be FULL OUTER JOINED with BondRate.  This is more than likely a mistake.
SELECT P.County_ID, 
	P.Parcel_ID, 
	P.Rate_ID, 
	P.Add_ID, 
	P.Exempt, 
	IIf(P.UnitAssessment=-1,P.UnitAssessmentValue,
			IIf(P.BuildHT>=4,(P.CTaxLand*(P.Benef*0.01))+((P.CTaxBuild/P.BuildHT)*3*(P.Benef*0.01))+((P.CTaxBuild/P.BuildHT)*(P.BuildHT-3)*0.06),
				IIf(P.Partial_Prot=-1,IIf(P.Bldg_Incl=-1,(P.CTaxLand*(P.Wet_Perc*0.01)*0.03)+(P.CTaxBuild*0.03),P.CTaxLand*(P.Wet_Perc*0.01)*0.03),(P.CTaxLand+P.CTaxBuild)*(P.Benef*0.01)))) AS dblBenefit, 
	BR.Bond_rate, 
	TR.Tax_Rate, 
	P.id, 
	P.UnitAssessment, 
	P.UnitAssessmentValue, 
	TR.TaxRate_Description, 
	P.MainCounty
FROM BondRate AS BR, MATCHEDTAXPARCELS AS P 
	INNER JOIN TaxRate AS TR ON P.Rate_ID=TR.CharCode

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