Multiple 'AND' conditions on same column - sql

Question

I'm using an Access 2007 database in ASP.Net where I need to extract data from a table if an item meets multiple 'AND' clauses.
For example:
Select * from tableA
where tableA.column1 = myvalue1
and (tableA.column2 = myvalue2
and tableA.column2 = myvalue3)
(The '(' and ')' parenthesis around the 'and' clauses are an Access requirement)
myvalue1 exists multiple times in column1 because column2 stores many different pieces of data for the column1 value.
However, I only want the results to show those column1 values which meet all of the column2 search criteria.
For example, column1 contains employee surnames, column2 contains the qualifications of the employee.
One employee in column1 may hold many qualifications in column2.
Searching with the 'OR' clause for employees who hold all the required qualifications for an assignment would produce a table with multiple rows for each employee.
What is required is a single row for each employee who holds every one of the required qualifications.
Let's say employee A has qualifications X, Y and Z. The employee's name will be in a row in column 1 each time a qualification is added to column2, so the employee's name appears in column1 3 times. Assume now employee B also has qualifications X, Y and Z but employee C has W, X and Y. If an assignment needs qualifications X,Y and Z I don't want employee C appearing in the results of a search as employee C won't hold the relevant qualifications.
When I use the above 'select' command with just one 'and' clause the search works fine, but with two 'and' clauses nothing is returned, even though I know there are items in column1 that meet both of the 'and' criteria.
What am I missing in the concatenation of the 'and' clauses?

Answer 1

The following solution will work, but performance will suffer. This will return 1 row per person, I can rewrite it to return both rows.
Select * from tableA
where tableA.column1 = myvalue1
and (tableA.column2 = myvalue2
and DCount("column2", "TableA", "column1 = """ & column1 & """ AND column2 = """ & myvalue3 & """" ) <> 0)
Your fundamental problem is that a select query without a group by or pivot clause only evaluates 1 row at a time. I'd probably pivot the data, concatenate it, and then evaluate it for better performance in the end. But that's more complicated, and requires more information on the table structure and what you want to do.

Answer 2

Based on new information, I'll submit this answer:
My gut feeling is that you can't do this in one simple query. This sounds cludgy, but I think you're going to need one query created that's a SELECT DISTINCT query, and that query will pull one record for each employee:
Select DISTINCT Column1 from tableA
Call this query something like qryEmployees
Next you're going to need to create a new table. Call it tblQualifications. It will contain 2 fields; EName and EQualifications. We're going to fill that in a minute.
Next you're going to need to loop through each record in qryEmployees and write the employee name and their qualifications into tblQualifications.
'Run through every Employee name
Do While qryEmployees.EOF = False
'Set up a temp variable, MyQual, and set it equal to Empty
MyQual = ""
'Pull all qualifications from TableA for the current Employee
Set rec = db.OpenRecordset ("Select Column1, column2 from TableA WHERE Column1 = '" & qryEmployees.Column1 & "'")
'Looping through the qualifications
Do While rec.EOF = False
'Add the qualification to the MyQual string
MyQual = MyQual & rec("Column2") & ", "
rec.MoveNext
Loop
'Now that we have all the qualifications in a string, trim off the last ", "
MyQual = left(MyQual, len(MyQual)-2)
'Open up tblQualifications and fill it with the Employee and a string of all of their qualifications
tblQualifications.AddNew
tblQualifications(0) = qryEmployees.Column1
tblQualifications(1) = MyQual
tblQualifications.Update
'Move on to the next Employee and repeat the process
qryEmployees.MoveNext
Loop
Now you have one table with Employee Name in one field, and all of his qualifications in the next. If you use the LIKE operator on this table, you should get your results.
Select * from tblQualifications
where tblQualifications.EName = myvalue1
and (tblQualifications.EQualifications LIKE myvalue2
and tblQualifications.EQualifications LIKE myvalue3)
It's not pretty, but it will work (with a little putzing with the code above, as I'm writing it off the top of my head and it's untested).

Answer 3

Thanks Johnny, your suggestion inspired me to write a slightly different approach to the solution.
I swapped the 'AND' to an 'OR' as others have suggested to extract any employee into a table if they have any of the qualifications.
The result is a table with every required qualification for every employee who has one of those qualifications.
I then did a count elsewhere of the number of qualifications required for the assignment and compared this to whether or not the employee had the required number of qualifications, as follows:
Dim objSearchTable As DataTable = DSSearch.Tables("Employees")
Dim i As Integer
If QualificationsCount > 0 Then
For i = 0 To objSearchTable.rows.count - 1
strEmployee = objSearchTable.Rows(i).Item("column1")
Dim foundRows As DataRow() = objSearchTable.[Select]("column1 = '" & strEmployee & "'")
Dim numberOfRecords As Integer = foundRows.count
If numberOfRecords < QualificationsCount Then
objSearchTable.Rows(i).Delete
End If
Next
End If
objSearchTable.AcceptChanges
This deletes every instance of an employee from the table if the count of qualifications is less than the number required.
The solution isn't as elegant as extracting only the correct employees from the database to begin with.
There is also an overhead on extracting every employee from the database, but the end result is a table with just one row for each employee with all the qualifications, which does what I need.