在存储过程中嵌套if语句

Question

I'm creating a stored procedure which needs to check several conditions, and depending on the outcome has to execute specific queries. I have trouble when it comes to nested IF-statements, and I really can't seem to figure out what's wrong with the syntax.

Here's a snippet of my code (the rest is pretty much the same, but with other values)

 IF @periodeKD = 'Formiddag'
  IF @Ugedagnr = '1'
        BEGIN TRANSACTION
                    @ModulID = 'S1'
                    @ModulID2 = 'S2'
                    INSERT INTO Undervisning (ModulID, SkemaDato, LokaleID, HoldID, FagID, LaererID, Aar, Uge)
                    VALUES (@ModulID, GETDATE(), @lokaleID, @holdID, @fagID, @laererID, @CurrentYear, @WeekNumber)
                    INSERT INTO Undervisning (ModulID, SkemaDato, LokaleID, HoldID, FagID, LaererID, Aar, Uge)
                    VALUES (@ModulID2, GETDATE(), @lokaleID, @holdID, @fagID, @laererID, @CurrentYear, @WeekNumber) 
        COMMIT TRANSACTION
  IF @Ugedagnr = '2'
        BEGIN TRANSACTION
                    @ModulID = 'S5'
                    @ModulID2 = 'S6'
                    INSERT INTO Undervisning (ModulID, SkemaDato, LokaleID, HoldID, FagID, LaererID, Aar, Uge)
                    VALUES (@ModulID, GETDATE(), @lokaleID, @holdID, @fagID, @laererID, @CurrentYear, @WeekNumber)
                    INSERT INTO Undervisning (ModulID, SkemaDato, LokaleID, HoldID, FagID, LaererID, Aar, Uge)
                    VALUES (@ModulID2, GETDATE(), @lokaleID, @holdID, @fagID, @laererID, @CurrentYear, @WeekNumber) 
        COMMIT TRANSACTION
  IF @Ugedagnr = '3'
        BEGIN TRANSACTION
                    @ModulID = 'S9'
                    @ModulID2 = 'S10'
                    INSERT INTO Undervisning (ModulID, SkemaDato, LokaleID, HoldID, FagID, LaererID, Aar, Uge)
                    VALUES (@ModulID, GETDATE(), @lokaleID, @holdID, @fagID, @laererID, @CurrentYear, @WeekNumber)
                    INSERT INTO Undervisning (ModulID, SkemaDato, LokaleID, HoldID, FagID, LaererID, Aar, Uge)
                    VALUES (@ModulID2, GETDATE(), @lokaleID, @holdID, @fagID, @laererID, @CurrentYear, @WeekNumber) 
        COMMIT TRANSACTION
  IF @Ugedagnr = '4'
        BEGIN TRANSACTION
                    @ModulID = 'S13'
                    @ModulID2 = 'S14'
                    INSERT INTO Undervisning (ModulID, SkemaDato, LokaleID, HoldID, FagID, LaererID, Aar, Uge)
                    VALUES (@ModulID, GETDATE(), @lokaleID, @holdID, @fagID, @laererID, @CurrentYear, @WeekNumber)
                    INSERT INTO Undervisning (ModulID, SkemaDato, LokaleID, HoldID, FagID, LaererID, Aar, Uge)
                    VALUES (@ModulID2, GETDATE(), @lokaleID, @holdID, @fagID, @laererID, @CurrentYear, @WeekNumber) 
        COMMIT TRANSACTION
  IF @Ugedagnr = '5'
        BEGIN TRANSACTION
                    @ModulID = 'S17'
                    @ModulID2 = 'S18'
                    INSERT INTO Undervisning (ModulID, SkemaDato, LokaleID, HoldID, FagID, LaererID, Aar, Uge)
                    VALUES (@ModulID, GETDATE(), @lokaleID, @holdID, @fagID, @laererID, @CurrentYear, @WeekNumber)
                    INSERT INTO Undervisning (ModulID, SkemaDato, LokaleID, HoldID, FagID, LaererID, Aar, Uge)
                    VALUES (@ModulID2, GETDATE(), @lokaleID, @holdID, @fagID, @laererID, @CurrentYear, @WeekNumber) 
        COMMIT TRANSACTION

It keeps complaining about the second IF-statement after the first one (IF @Ugedagnr = '1').

How are nested IF-statements written?

Answer 1

IF @periodeKD = 'Formiddag'
BEGIN
  IF @Ugedagnr = '1'
  BEGIN
        BEGIN TRANSACTION
                    SET @ModulID = 'S1'
                    SET @ModulID2 = 'S2'
                    INSERT INTO Undervisning (ModulID, SkemaDato, LokaleID, HoldID, FagID, LaererID, Aar, Uge)
                    VALUES (@ModulID, GETDATE(), @lokaleID, @holdID, @fagID, @laererID, @CurrentYear, @WeekNumber)
                    INSERT INTO Undervisning (ModulID, SkemaDato, LokaleID, HoldID, FagID, LaererID, Aar, Uge)
                    VALUES (@ModulID2, GETDATE(), @lokaleID, @holdID, @fagID, @laererID, @CurrentYear, @WeekNumber) 
        COMMIT TRANSACTION
  END
  ELSE
  IF @Ugedagnr = '2'
  BEGIN
        BEGIN TRANSACTION
                    SET @ModulID = 'S5'
                    SET @ModulID2 = 'S6'
                    INSERT INTO Undervisning (ModulID, SkemaDato, LokaleID, HoldID, FagID, LaererID, Aar, Uge)
                    VALUES (@ModulID, GETDATE(), @lokaleID, @holdID, @fagID, @laererID, @CurrentYear, @WeekNumber)
                    INSERT INTO Undervisning (ModulID, SkemaDato, LokaleID, HoldID, FagID, LaererID, Aar, Uge)
                    VALUES (@ModulID2, GETDATE(), @lokaleID, @holdID, @fagID, @laererID, @CurrentYear, @WeekNumber) 
        COMMIT TRANSACTION
  END
  ELSE
  ...
END

Note, syntax @ModulID = 'S1' is illegal. Use SET @ModulID = 'S1' .

Mapping between @Ugedagnr and @Modul* can be easily implemented via map table and single select instead of bunch of IFs.

Answer 2

Since you are checking one variable against multiple conditions, therefore, you should use something like this Here the block of code where the condition is true will be executed and other blocks will be ignored.

IF (@ParentVar1 Condition1)
Begin
       IF(@Var1 Condition1)
             BEGIN
              /*Your Code Goes here*/
             END

       ELSE IF(@Var1 Condition2)
              BEGIN
                /*Your Code Goes here*/ 
              END 
       ELSE IF(@Var1 Condition2)
              BEGIN
                /*Your Code Goes here*/ 
              END 
       ELSE IF(@Var1 Condition2)
              BEGIN
                /*Your Code Goes here*/ 
              END 
       ELSE      --<--- Default Task if none of the above is true
             BEGIN
               /*Your Code Goes here*/
             END
End

Answer 3

If your insert statements are the same, then you can use the following code snippet:

DECLARE @Ugedagnr VARCHAR(10) = '1',
    @ModulID VARCHAR(10),
    @ModulID2 VARCHAR(10);

IF @Ugedagnr = '1'
BEGIN
    IF @Ugedagnr = '1'
    BEGIN
        SET @ModulID = 'S1';
        SET @ModulID2 = 'S2';
    END;

    IF @Ugedagnr = '2'
    BEGIN
        SET @ModulID = 'S5';
        SET @ModulID2 = 'S6';
    END;

    IF @Ugedagnr = '3'
    BEGIN
        SET @ModulID = 'S9';
        SET @ModulID2 = 'S10';
    END;
    IF @Ugedagnr = '4'
    BEGIN
        SET @ModulID = 'S13';
        SET @ModulID2 = 'S14';
    END;
    IF @Ugedagnr = '5'
    BEGIN
        SET @ModulID = 'S17';
        SET @ModulID2 = 'S18';
    END;

    SELECT @ModulID, @ModulID2


    BEGIN TRANSACTION
                    @ModulID = 'S9'
                    @ModulID2 = 'S10'
                    INSERT INTO Undervisning (ModulID, SkemaDato, LokaleID, HoldID, FagID, LaererID, Aar, Uge)
                    VALUES (@ModulID, GETDATE(), @lokaleID, @holdID, @fagID, @laererID, @CurrentYear, @WeekNumber)
                    INSERT INTO Undervisning (ModulID, SkemaDato, LokaleID, HoldID, FagID, LaererID, Aar, Uge)
                    VALUES (@ModulID2, GETDATE(), @lokaleID, @holdID, @fagID, @laererID, @CurrentYear, @WeekNumber) 
    COMMIT TRANSACTION
END;