Build SQL query string using user input

Question

I have to make a string by using the values which the user selects on the webpage,

Suppose I need to display files for multiple machines with different search criteria...

I currently use this code:

DataTable dt = new DataTable();
SqlConnection connection = new SqlConnection();
connection.ConnectionString = ConfigurationManager
               .ConnectionStrings["DBConnectionString"].ConnectionString;
connection.Open();
SqlCommand sqlCmd = new SqlCommand
  ("SELECT FileID FROM Files
    WHERE MachineID=@machineID and date= @date", connection);
SqlDataAdapter sqlDa = new SqlDataAdapter(sqlCmd);

sqlCmd.Parameters.AddWithValue("@machineID", machineID);
sqlCmd.Parameters.AddWithValue("@date", date);

sqlDa.Fill(dt);

Now this is a fixed query where the user just has one machine and just selects one date...

I want to make a query in which the user has multiple search options like type or size if he/she wants depending on what he/she selects.

Also if he/she can select multiple machines...

SELECT FileID FROM Files
WHERE (MachineID=@machineID1 or MachineID = @machineID2...)
AND (date= @date and size=@size and type=@type... )

All of this happens at runtime... otherwise I have to create a for loop to put multiple machines one by one... and have multiple queries depending on the case the user selected...

This is quite interesting and I could use some help...

Answer 1

You can use WHERE MachineID IN ('Machine1', 'Machine2', 'Machine3', ... 'MachineN')

Then in your loop you would just add the 1..n machines. The IN clause works with 1 element or n elements, so it should be fine.

However, I'd look at using a stored procedure to do it rather than hardcoding the SQL into your application.

Answer 2

Build a real table and load the machine ids into it.

Then your SQL would be:

where MachineID in ( select MachineID from userMachine where userID = x)

When you are done, remove all rows for the userID:

delete from userMachine where userID = x.

Answer 3

If you are going to do this via dynamic SQL, you need to build a call to the IN function. (e.g. In(id1, id2, id3...)

private string GetSql( IList<int> machineIds )
{
    var sql = new StringBuilder( "SELECT FileID FROM Files Where MachineID In(" );
    for( var i = 0; i < machineIds.Count; i++ )
    {
        if ( i > 0 )
            sql.Append(", ")
        sql.Append("@MachineId{0}", i);
    }

    sql.Append(" ) ");

    //additional parameters to query
    sql.AppendLine(" And Col1 = @Col1" );
    sql.AppendLine(" And Col2 = @Col2 ");
    ...

    return sql.ToString();
}

private DataTable GetData( IList<int> machineIds, string col1, int col2... )
{
    var dt = new DataTable();
    var sql = GetSql( machineIds );
    using ( var conn = new SqlConnection() )
    {
        conn.ConnectionString = ConfigurationManager.ConnectionStrings["DBConnectionString"].ConnectionString;
        using ( var cmd = new SqlCommand( sql, conn ) )
        {
            conn.Open();

            for( var i = 0; i < machineIds.Count; i++ )
            {
                var parameterName = string.Format("@MachineId{0}", i );
                cmd.Parameters.AddWithValue( parameterName, machineIds[i] );
            }

            cmd.Parameters.AddWithValue( "@Col1", col1 ); 
            cmd.Parameters.AddWithValue( "@Col2", col2 ); 
            ...

            using ( var da = new SqlDataAdapter( cmd ) )
            {
                da.Fill( dt );
            }
        }
    }

    return dt;
}

Answer 4

Ideally you are trying to arrive at a solution similar to creating "MachineID in (1, 2, 3, 4)" dynamically.

Option 1

There are many ways to complete this task from passing in a comma separated string into the stored proc and dynamically build the sql string and then calling "EXEC sp_executesql @sql" WHERE IN (array of IDs)

Option 2

You can pass in a string of comma separated values and then parse out the values into their own temp-table and then join on to it http://vyaskn.tripod.com/passing_arrays_to_stored_procedures.htm

Option 3 - my choice

You can now pass in the array of values using XML and then select the array items easily. http://support.microsoft.com/kb/555266

.

Answer 5

I would also recommend using a stored procedure because otherwise you will leave yourself open to an SQL injection attack - especially where you are building up a string based on user input.

Something like:

a' or 1=1; -- Do bad things

You can use sp_executesql in SQL to run an SQL statement that is built up with a where clause like @dcp suggests and although it wouldn't optimize well it is probably a quick command to run anyway.

SQL Injection attacks by example

One way to achieve this would be using charindex. This example demonstrates how a stored procedure could be run when passed a space separated list of ids:

declare @machine table (machineId int, machineName varchar(20))
declare @files table (fileId int, machineId int)

insert into @machine (machineId, machineName) values (1, 'machine')
insert into @machine (machineId, machineName) values (2, 'machine 2.0')
insert into @machine (machineId, machineName) values (3, 'third machine')
insert into @machine (machineId, machineName) values (4, 'machine goes forth')
insert into @machine (machineId, machineName) values (5, 'machine V')

insert into @files (fileId, machineId) values (1, 3)
insert into @files (fileId, machineId) values (2, 3)
insert into @files (fileId, machineId) values (3, 2)
insert into @files (fileId, machineId) values (4, 1)
insert into @files (fileId, machineId) values (5, 3)
insert into @files (fileId, machineId) values (6, 5)

declare @machineText1 varchar(100)
declare @machineText2 varchar(100)
declare @machineText3 varchar(100)

set @machineText1 = '1 3 4'
set @machineText2 = '1'
set @machineText3 = '5 6'

select * from @files where charindex(rtrim(machineId), @machineText1, 1) > 0
-- returns files 1, 2, 4 and 5

select * from @files where charindex(rtrim(machineId), @machineText2, 1) > 0
-- returns file 4

select * from @files where charindex(rtrim(machineId), @machineText3, 1) > 0
--returns file 6

So you can create this stored procedure to achieve your aim:

create procedure FilesForMachines (@machineIds varchar(1000))
as
select * from [Files] where charindex(rtrim(machineId), @machineIds, 1) > 0

The charindex tip is from BugSplat.

Answer 6

Normally when I want to create a "search" type query, I use optional parameters. This allows me to send something or nothing to the parameter, making the query go from vague to very specific.

Example:

SELECT
  COL1,
  COL2,
  COL3
FROM TABLE
WHERE (@COL1 IS NULL OR @COL1 = '' OR @COL1 = COL1)

As you'll notice above, if you pass in NULL or BLANK it won't add the parameter to the query. If you do enter a value, then it'll be used in the comparison.