asked on

IF statement execution dependant on record count

I want to perform a series of actions on a table, but only if there are records in the table.

The table name will eventually be passed as parameter to the stored procedure, so the table name in the SELECT COUNT statement can change.

I'm struggling with the syntax and would appreciate some help. I'm getting the following error:

Server: Msg 137, Level 15, State 2, Line 17
Must declare the variable '@tableName'.

I have declared the variable so I must be doing something else wrong. Does anyone have any suggestions on how to fix this, or perhaps a better way to achieve the same thing?

Code being used:

DECLARE @type int, @tableName varchar(200), @numRecords int

SET @type = 7

IF @type = 7
BEGIN
SET @tableName = 'table1'
END
ELSE
BEGIN
SET @tableName = 'table2'
END

SELECT @numRecords= COUNT(*) FROM @tableName

-- only try and transfer records if some exist
IF (@numRecords) > 0
BEGIN
PRINT 'There are records in the table'
END

indu_mk

Replace SELECT @numRecords= COUNT(*) FROM @tableName
with
declare @sql varchar(8000)
set @sql = 'SELECT @numRecords= COUNT(*) FROM ' + @tableName
exes(@sql)

hongjun

Try this

DECLARE @type int, @tableName varchar(200), @numRecords int
Declare @SQL varchar(255)

SET @type = 7

IF @type = 7
BEGIN
SET @tableName = 'table1'
END
ELSE
BEGIN
SET @tableName = 'table2'
END

Set @SQL = 'SELECT @numRecords = COUNT(*) FROM [' + @tableName + ']'
Execute (@SQL)

-- only try and transfer records if some exist
IF (@numRecords) > 0
BEGIN
PRINT 'There are records in the table'
END

hongjun

indu_mk

sorry for the typo, its exec not exes

ian_r

ASKER

Thanks. The two suggestions look the same to me, and I've just tried the code that hongjun supplied, but I'm now getting the error:

Server: Msg 137, Level 15, State 1, Line 1
Must declare the variable '@numRecords'.

Which is strange because @numRecords is declared. I'll continue to play around with it, unless anyone know's why it's failing?

Maybe I've just been staring at it for too long...

hongjun

Try this

DECLARE @type int, @tableName varchar(200)
Declare @SQL varchar(255)

SET @type = 7

IF @type = 7
BEGIN
SET @tableName = 'table1'
END
ELSE
BEGIN
SET @tableName = 'table2'
END

Execute ('
      Declare @numRecords int
      SELECT @numRecords=COUNT(*) FROM ' + @tableName +
      '-- only try and transfer records if some exist
      IF (@numRecords) > 0
      BEGIN
       PRINT ''There are records in the table''
      END
'
)

ASKER CERTIFIED SOLUTION

indu_mk

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SOLUTION

Guy Hengel [angelIII / a3]

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Lowfatspread

you shouldn't write procedures like this ...
this is a very poor style and requires dynamic sql to provide the result....
which can lead to all sorts of security and performance issues...

you need to re-evaluate your requirements...

what are you actually trying to achieve?
in what circumstance do you need the information?
(dynamic sql can be ok in a System management sense...)