Using Nested IF ELSE statements in sql

Question

When any one of the following conditions is met, I want the code to go to the next execution step:

1. First Name, Last Name and DOB : all three are not blank
2. ID and DOB are not blank
3. SSN and DOB are not blank
4. ID and Group Number are not blank

Below is the code I have. When I run it by providing First Name, Last Name and DOB (condition 1 is satisfied), it still fails saying condition 4 is not met. Can someone tell me what am I doing wrong?

IF ( ( @FirstName IS NULL 
        OR Len(Ltrim(@FirstName)) = 0 ) 
     AND ( @LastName IS NULL 
            OR Len(Ltrim(@LastName)) = 0 ) 
     AND ( @DOB IS NULL ) ) 
  BEGIN 
      INSERT INTO @ValidationError 
                  (errormessage) 
      VALUES      ( 'first name, last name and Date of Birth must be specified.' 
      ) 
  END 
ELSE 
  BEGIN 
      IF ( @DOB IS NULL 
           AND @Id IS NULL ) 
        BEGIN 
            INSERT INTO @ValidationError 
                        (errormessage) 
            VALUES      ( 'Date of Birth and Id must be specified.' ) 
        END 
      ELSE 
        BEGIN 
            IF ( @DOB IS NULL 
                 AND @SSN IS NULL ) 
              BEGIN 
                  INSERT INTO @ValidationError 
                              (errormessage) 
                  VALUES      ( 'Date of Birth and SSN must be specified.' ) 
              END 
            ELSE 
              BEGIN 
                  IF ( @Id IS NULL 
                       AND @GroupNumber IS NULL ) 
                    BEGIN 
                        INSERT INTO @ValidationError 
                                    (errormessage) 
                        VALUES      ( 'Id and Group Number must be specified.' ) 
                    END 
              END 
        END 
  END 

Answer 1

A CASE statement would be simpler:

INSERT INTO @ValidationError  (errormessage)  
SELECT CASE WHEN Criteria1 THEN 'first name, last name and Date of Birth must be specified.'
            WHEN Criteria2 THEN 'Date of Birth and Id must be specified.'
            WHEN Criteria3 THEN 'Date of Birth and SSN must be specified.'  
            WHEN Criteria4 THEN 'Id and Group Number must be specified.'        
       END

As far as the error in your syntax, you've got extraneous BEGIN and END, I believe the following will work:

IF ( ( @FirstName IS NULL OR Len(Ltrim(@FirstName)) = 0 ) 
     AND ( @LastName IS NULL OR Len(Ltrim(@LastName)) = 0 ) 
     AND ( @DOB IS NULL ) ) 
    BEGIN 
          INSERT INTO @ValidationError 
                      (errormessage) 
          VALUES      ( 'first name, last name and Date of Birth must be specified.') 
    END 
ELSE IF ( @DOB IS NULL AND @Id IS NULL ) 
    BEGIN 
        INSERT INTO @ValidationError 
                    (errormessage) 
        VALUES      ( 'Date of Birth and Id must be specified.' ) 
    END 
ELSE IF ( @DOB IS NULL AND @SSN IS NULL ) 
    BEGIN 
        INSERT INTO @ValidationError 
                    (errormessage) 
        VALUES      ( 'Date of Birth and SSN must be specified.' ) 
    END 
ELSE IF ( @Id IS NULL AND @GroupNumber IS NULL ) 
    BEGIN 
        INSERT INTO @ValidationError 
                    (errormessage) 
        VALUES      ( 'Id and Group Number must be specified.' ) 
    END