SQL error Msg 156, Level 15, if 2 = 3 enter to make the select. HELP

    CREATE TABLE bit13
    (
        ID          INT IDENTITY(1, 1) PRIMARY KEY,
        campo_pk    VARCHAR(100)
    )
DECLARE @campo_pk  VARCHAR(100),
    @campo_pk2 VARCHAR(100),    
    @campo_pk3 VARCHAR(100)

SET @campo_pk   = (SELECT campo_pk  FROM bit13 WHERE ID = 1)
SET @campo_pk2  = (SELECT campo_pk  FROM bit13 WHERE ID = 2)
SET @campo_pk3  = (SELECT campo_pk  FROM bit13 WHERE ID = 3)

DECLARE @SQL NVARCHAR(100)
SET @SQL = (select count(*) from bit13)

EXEC('


IF ('+@SQL+' = 2)
    BEGIN
        IF (SELECT COUNT(*) FROM bit13 WHERE ID = 2) > 0
            BEGIN
                SELECT '+@campo_pk2+' FROM exp10 
            END
    END
IF ('+@SQL+' = 3)
    BEGIN
        IF (SELECT COUNT(*) FROM bit13 WHERE ID = 2) > 0
            BEGIN
                SELECT '+@campo_pk2+' FROM exp10
            END
        IF (SELECT COUNT(*) FROM bit13 WHERE ID = 3) > 0 
            BEGIN
                SELECT '+@campo_pk3+' FROM exp10
            END
    END

')

I have the following problem, I try to generate a bitacora by means of triggers, I have several tables with primary keys composed, so, in table bit13 I store the primary keys of a table, my tables can have up to 5 or 6 primary keys . @sql contains the number of primary keys Let's suppose that I bring 3 primary keys according to the code inside the exec (field_pk, field_pk2, field_pk3), so what happens if I decide to take a table of two primary keys having my code in case they are 2 and 3 primary keys.

If @sql is 2, then ask me the value of field_pk2 only If @sql is 3, then ask me the value of field_pk2 and field_pk3 only.

in this case, @sql is 2, and therefore you should only bring me campo_pk2, in this case, there are two conditions @sql = 2 and @sql = 3, because if @sql = 2 go to @sql = 3 and it marks me an error

  

Msg 156, Level 15, State 1, Line 17   Incorrect syntax near the keyword 'FROM'.

I understand that bit13 does not contain the field_pk3 so it should mark error, but comment that last line

IF (SELECT COUNT(*) FROM bit13 WHERE ID = 3) > 0 
                BEGIN
                    SELECT '+@campo_pk3+' FROM exp10
                END

and it does not show me any error.

I do not know if you explain me well, someone who can help me?

Thanks greetings!.