SQL conditional SELECT

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