Injecting variable in nested EXEC in stored procedure

Question

New to SQL and i'm working on a separate.network so i can't share snippets (sorry) so bare with me please.

I have a stored procedure that has a table injected, based on this table i want it to run a specific part of the script (if else else if...)

Before I start adding the ELSEs i want to ensure the IF first works.
It goes something like this within my alter procedure:

ALTER PROCEDURE dbo.TestProc (@table VARCHAR(50))
AS
BEGIN
DECLARE @sql AS VARCHAR(MAX)
SET @sql = 
   N'IF EXISTS (SELECT PersonID FROM ' + @table + ')
      BEGIN 
      EXEC SP_EXECUTIONSQL N''''
         INSERT INTO dbo.TEST(PerID, Name, Age) SELECT T.PerID, T.Name, T.Age 
         FROM ''' + @table + ''' T  
         END' 
-- Before the apostrophe on the END i'd add the else, but again, i want to test this first.   
EXEC (SQL); 
END

The issue i'm having when i run EXEC TestProc 'Employees' is Incorrect syntax near 'Employees' - the nested injected @table in the second FROM.

For background, I am nesting the EXEC SP_EXECUTIONSQL Because i was having the same issue as this person .
Also, i simplified my table significantly for various reasons, so alternative solutions may not be feasible.

I tried just using IF ELSE statements normally, but i discovered from a previously posted question that everything is compiled before the IF statement, and so the injected table overrides the IF statement and injects it into IF and every ELSE i throw in there.

What i was expecting was for the script to stop once the conditions of the IF ELSE were met.

Answer 1

You have quotes that your shouldn't and missing quotes that you need. You also have a typo so_executionsql should be sp_executesql .

I reformatted your code to make it easier.

Try this...

SET @sql = N'
  IF EXISTS (SELECT PersonID FROM ' + QUOTENAME(@TABLE) + ')
  BEGIN 
    EXEC SP_EXECUTESQL N''
      INSERT INTO dbo.TEST(PerID, Name, Age)
        SELECT T.PerID, T.Name, T.Age 
        FROM ' + QUOTENAME(@TABLE) + ' T
    '';
  END
'

In fact, you don't even need the nested calls to exec...

SET @sql = N'
  IF EXISTS (SELECT PersonID FROM ' + QUOTENAME(@TABLE) + ')
  BEGIN
    INSERT INTO dbo.TEST(PerID, Name, Age)
      SELECT T.PerID, T.Name, T.Age 
      FROM ' + QUOTENAME(@TABLE) + ' T;
  END
'