How to get row count from EXEC() in a TSQL SPROC? - tsql

Question

I have a TSQL sproc that builds a query as and executes it as follows:
EXEC (#sqlTop + #sqlBody + #sqlBottom)
#sqlTop contains something like SELECT TOP(x) col1, col2, col3...
TOP(x) will limit the rows returned, so later I want to know what the actual number of rows in the table is that match the query.
I then replace #sqlTop with something like:
EXEC ('SELECT #ActualNumberOfResults = COUNT(*) ' + #sqlBody)
I can see why this is not working, and why a value not declared error occurs, but I think it adequately describes what I'm trying to accomplish.
Any ideas?

Answer 1

use sp_executesql and an output parameter
example
DECLARE #sqlBody VARCHAR(500),#TableCount INT, #SQL NVARCHAR(1000)
SELECT #sqlBody = 'from sysobjects'
SELECT #SQL = N'SELECT #TableCount = COUNT(*) ' + #sqlBody
EXEC sp_executesql #SQL, N'#TableCount INT OUTPUT', #TableCount OUTPUT
SELECT #TableCount
GO

Answer 2

You could instead have the dynamic query return the result as a row set, which you would then insert into a table variable (could be a temporary or ordinary table as well) using the INSERT ... EXEC syntax. Afterwards you can just read the saved value into a variable using SELECT #var = ...:
DECLARE #rowcount TABLE (Value int);
INSERT INTO #rowcount
EXEC('SELECT COUNT(*) ' + #sqlBody);
SELECT #ActualNumberOfResults = Value FROM #rowcount;

Answer 3

Late in the day, but I found this method much simpler:
-- test setup
DECLARE #sqlBody nvarchar(max) = N'SELECT MyField FROM dbo.MyTable WHERE MyOtherField = ''x''';
DECLARE #ActualNumberOfResults int;
-- the goods
EXEC sp_executesql #sqlBody;
SET #ActualNumberOfResults = ##ROWCOUNT;
SELECT #ActualNumberOfResults;

Answer 4

After executing your actual query store the result of ##ROWCOUNT in any variable which you can use later.
EXEC sp_executesql 'SELECT TOP 10 FROM ABX'
SET #TotRecord = ##ROWCOUNT into your variable for later use.

Answer 5

Keep in mind that dynamic SQL has its own scope. Any variable declared/modified there will go out of scope after your EXEC or your sp_executesql.
Suggest writing to a temp table, which will be in scope to your dynamic SQL statement, and outside.
Perhaps put it in your sqlBottom:
CREATE TABLE ##tempCounter(MyNum int);
EXEC('SELECT #ActualNumberOfResults = COUNT(*) ' + #sqlBody +
'; INSERT INTO ##tempCounter(MyNum) VALUES(#ActualNumberOfResults);');
SELECT MyNum FROM ##tempCounter;

Answer 6

You can use output variable in SP_EXECUTESQL
DECLARE #SQL NVARCHAR(MAX);
DECLARE #ParamDefinition NVARCHAR(100) = '#ROW_SQL INT OUTPUT'
DECLARE #AFFECTED_ROWS INT;
SELECT
#SQL = N'SELECT 1 UNION ALL SELECT 2'
SELECT #SQL += 'SELECT #ROW_SQL = ##ROWCOUNT;';
EXEC SP_EXECUTESQL #SQL, #ParamDefinition, #ROW_SQL=#AFFECTED_ROWS OUTPUT;
PRINT 'Number of affected rows: ' + CAST(#AFFECTED_ROWS AS VARCHAR(20));
Ouput:
SQL2.sql: Number of affected rows: 2
Thanks Jesus Fernandez!

Answer 7

The only problem with the answers that create temporary tables (either using "DECLARE #rowcount TABLE" or "CREATE TABLE ##tempCounter(MyNum int)") is that you're having to read all the affected records off disk into memory. If you're expecting a large number of records this may take some time.
So if the answer is likely to be large the "use sp_executesql and an output parameter" solution is a more efficient answer. And it does appear to work.