Select statment from multiple tables, with variable input

Question

I have two tables: AreaCode and EquipmentNumber.

+------------------------------------+
| AreaCd                             |
|---         


        

Answer 1

Try this

  SELECT Number, Type, Code FROM EqNum, AreaCd " +
   "WHERE EqNum.AreaId = AreaCd.AreaId AND 
   isnull(Code,0) = " + int nCode + " or
    isnull(Number,0) = '" + string sNumber + "' or isnull(Type,0) = '" + string sType + "'

Answer 2

SELECT e.Number, e.Type, a.Code
FROM EqNum e INNER JOIN AreaCd a
ON e.AreaId = a.AreaId
WHERE (@Number IS NULL OR e.Number = @Number)
AND (@Type IS NULL OR e.Type = @Type)
AND (@Code IS NULL OR a.Code = @Code)

To learn how to use parameters with ADO.NET, click here.

Setting parameters would look something like this:

command.Parameters["@Number"].Value = (string.IsNullOrEmpty(number) ? (object) DBNull.Value : number);

Answer 3

I think this is what you are after :

Just added a simple trick;

if(string.IsNullOrEmpty(sNumber))
    sNumber="$$$";               //If sNumber is empty, then selection using sNumber= '$$$' will return nothing.
if(string.IsNullOrEmpty(sType))
    sType="$$$"                 //If sType is empty, then selection using sType = '$$$' will return nothing.
"SELECT Number, Type, Code FROM EqNum, AreaCd " +
"WHERE EqNum.AreaId = AreaCd.AreaId 
AND 
  (Code = " + int nCode + " 
   OR Number = '" + string sNumber + "' 
   OR Type = '" + string sType + "')"

OR using LIKE:

if(string.IsNullOrEmpty(sNumber))
    sNumber="$$$";             //If sNumber is empty, then selection using sNumber LIKE '%$$$%' will return nothing.
if(string.IsNullOrEmpty(sType))
    sType="$$$"                //If sType is empty, then selection using sType LIKE '%$$$%' will return nothing.
"SELECT Number, Type, Code FROM EqNum, AreaCd " +
"WHERE EqNum.AreaId = AreaCd.AreaId 
AND 
  (Code = " + int nCode + "
   OR Number LIKE '%" + string sNumber + "%' 
   OR Type LIKE '%" + string sType + "%')"

See an example at SQL Fiddle