SQL Query performance with if exists - sql

Question

I have this SQL query:
IF NOT EXISTS (SELECT TOP 1 RowId
FROM dbo.Cache AS C
WHERE StringSearched = #pcpnpi
AND colName = 'pcpnpi'
AND ModifiedAt > (SELECT ModifiedAt
FROM dbo.Patients AS p
WHERE P.RowID = C.RowID))
BEGIN
SELECT #constVal = FunctionWeight
FROM dbo.FunctionWeights
WHERE FunctionWeights.FunctionId = 33;
INSERT INTO #Temp2
(RowNumber,ValFromUser,ColumnName,ValFromFunc,
FuncWeight,percentage)
SELECT RowNumber,#pcpnpi,'pcpnpi',PercentMatch,
#constVal,PercentMatch * #constVal
FROM dbo.Matchpcpnpi (#pcpnpi);
END
ELSE
BEGIN
INSERT INTO #Temp2
(RowNumber,ValFromUser,ColumnName,Percentage)
SELECT RowId,StringSearched,ColName,PercentMatch
FROM dbo.Cache AS C
WHERE StringSearched = #pcpnpi
AND colName = 'pcpnpi'
AND ModifiedAt > (SELECT ModifiedAt
FROM dbo.Patients AS p
WHERE P.RowID = C.RowID)
END
The above if statement is meant to avoid unnecessary look ups for strings that have already been searched earlier and MatchPercent has been calculated. In that case, it is directly retrieved from Cache table.
Above sql query is basically for one particular column and this same kind of query with just columnName and its value changing is repeated for many other columns in the procedure.
The if Exists check was obviously meant so that query performance could improve however the performance has gone down, probably because of extra checks.
Cache table which is actually meant to improve the performance, extra checks have ruined it.
Is there a way to simplify above query,please ? Any directions on same will help.
Thanks

Answer 1

First insert into #temp2 based on exists condition. If the Insert record count is zero then do the another insert. Try this.
INSERT INTO #Temp2
(RowNumber,ValFromUser,ColumnName,Percentage)
SELECT RowId,StringSearched,ColName,PercentMatch
FROM dbo.Cache AS C
WHERE StringSearched = #pcpnpi
AND colName = 'pcpnpi'
AND ModifiedAt > (SELECT ModifiedAt
FROM dbo.Patients AS p
WHERE P.RowID = C.RowID)
IF ##ROWCOUNT = 0
BEGIN
SELECT #constVal = FunctionWeight
FROM dbo.FunctionWeights
WHERE FunctionWeights.FunctionId = 33;
INSERT INTO #Temp2
(RowNumber,ValFromUser,ColumnName,ValFromFunc,
FuncWeight,percentage)
SELECT RowNumber,#pcpnpi,'pcpnpi',PercentMatch,
#constVal,PercentMatch * #constVal
FROM dbo.Matchpcpnpi (#pcpnpi)
END

Answer 2

First, consider this query in the exists:
select Top 1 RowId
from dbo.Cache as C
where StringSearched = #pcpnpi and
colName = 'pcpnpi' and
ModifiedAt > ( Select ModifiedAt FROM dbo.Patients p WHERE P.RowID = C.RowID))
For performance, you want indexes on cache(StringSearched, colName, ModifiedAt, RowId) and Patients(RowId).
However, you are running this query twice. I would suggest a structure more like:
declare #RowId . . . ; -- I don't know the type
select Top 1 #RowId = RowId
from dbo.Cache as C
where StringSearched = #pcpnpi and
colName = 'pcpnpi' and
ModifiedAt > ( Select ModifiedAt FROM dbo.Patients p WHERE P.RowID = C.RowID));
if (#RowId) is null . ..
else . . .