SQL conditional SELECT

Question

Hi

I would like to create a stored procedure with parameters that indicate which fields should be selected.

E.g. I would like to pass two parameters "selectField1" and "selectField2" each as bools.

Then I want something like

SELECT

if (selectField1 = true) Field1 ELSE do not select Field1

if (selectField2 = true) Field2 ELSE  do not select Field2

FROM Table

Thanks Karl

Answer 1

In SQL, you do it this way:

SELECT  CASE WHEN @selectField1 = 1 THEN Field1 ELSE NULL END,
        CASE WHEN @selectField2 = 1 THEN Field2 ELSE NULL END
FROM    Table

Relational model does not imply dynamic field count.

Instead, if you are not interested in a field value, you just select a NULL instead and parse it on the client.

Answer 2

You want the CASE statement:

SELECT
  CASE 
    WHEN @SelectField1 = 1 THEN Field1
    WHEN @SelectField2 = 1 THEN Field2
    ELSE NULL
  END AS NewField
FROM Table

EDIT: My example is for combining the two fields into one field, depending on the parameters supplied. It is a one-or-neither solution (not both). If you want the possibility of having both fields in the output, use Quassnoi's solution.

Answer 3

This is a psuedo way of doing it

IF (selectField1 = true) 
SELECT Field1 FROM Table
ELSE
SELECT Field2 FROM Table

Answer 4

what you want is:

 MY_FIELD=
  case 
   when (selectField1 = 1) then Field1
                                 else Field2     
  end,

in the select

However, y don't you just not show that column in your program?

Answer 5

Sounds like they wants the ability to return only fields that are allowed which means the number of fields returned also has to be dynamic. This will work with 2 variables. Anything more than than will be getting confusing.

IF (selectField1 = true AND selectField2 = true)
BEGIN
   SELECT Field1, Field2
   FROM Table
END
ELSE IF (selectField1 = true)
BEGIN
   SELECT Field1
   FROM Table
END
ELSE IF (selectField2 = true)
BEGIN
   SELECT Field2
   FROM Table
END

Dynamic SQL will help with multiples. This examples is assuming atleast 1 column is true.

DECLARE @sql varchar(MAX)
SET @sql = 'SELECT '
IF (selectField1 = true)
BEGIN
   SET @sql = @sql + 'Field1, '
END
IF (selectField2 = true)
BEGIN
   SET @sql = @sql + 'Field2, '
END
...
-- DROP ', '
@sql = SUBSTRING(@sql, 1, LEN(@sql)-2)

SET @sql = @sql + ' FROM Table'

EXEC(@sql)

Answer 6

@selectField1 AS bit
@selectField2 AS bit

SELECT
CASE 
    WHEN @selectField1 THEN Field1
    WHEN @selectField2 THEN Field2
    ELSE someDefaultField
END
FROM Table

Is this what you're looking for?

Answer 7

@Justin Balvanz, your code gives me a Syntax error, is there something missing from that, which is understood to be there and I am missing it out?, Thanks