asked on

Delphi SQL 'And/Or' Problem

I want the code to return 18-year-olds who scored grade A,B or C. Instead it gives me all ages who scored A, B, Or C. I'm confused by the use of 'Where/And/Or' in an SQL statement, particularly applied to Delphi code. Help much appreciated.

Qresults.Active:=True;
Qresults.SQL.Clear;
Qresults.SQL.Add('SELECT * FROM ResultsTable');
Qresults.SQL.Add('WHERE age:=+IntToStr(18));
Qresults.SQL.Add('AND  Grade='+QuotedStr('A'));
Qresults.SQL.Add('OR Grade='+QuotedStr('B'));
Qresults.SQL.Add('OR Grade='+QuotedStr('C'));
Qresults.Open;

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FactorB

Looks like you need some brackets, try it this way:

Qresults.Active:=True;
Qresults.SQL.Clear;
Qresults.SQL.Add('SELECT * FROM ResultsTable');
Qresults.SQL.Add(' WHERE (age:='+IntToStr(18));
Qresults.SQL.Add(' AND (Grade='+QuotedStr('A'));
Qresults.SQL.Add(' OR Grade='+QuotedStr('B'));
Qresults.SQL.Add(' OR Grade='+QuotedStr('C')+'))');
Qresults.Open;

Regards,
B.

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FactorB

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SOLUTION

8080_Diver

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nickjfox

ASKER

OK, I gave a simplified version of my problem in the hope that once I grasped the concept I'd be able to do the rest myself. So, thanks, to both of you, I'm almost there. But I still seem a bracket short? Or one bracket too many? I count five extra brackets but it won't work.

QResullts.SQL.Clear;
QResullts.SQL.Add('SELECT * FROM ResultsTable');
QResullts.SQL.Add('WHERE (age<='+IntToStr(18));
QResullts.SQL.Add('AND (passed>'+IntToStr(0));
QResullts.SQL.Add('AND (pass_Type<>null');
QResullts.SQL.Add('AND (Overwork<>null');
QResullts.SQL.Add(' AND (Grade='+QuotedStr('A'));
QResullts.SQL.Add(' OR Grade='+QuotedStr('G'));
QResullts.SQL.Add(' OR  Grade='+QuotedStr('I'));
QResullts.SQL.Add(' OR Grade='+QuotedStr('HA'));
QResullts.SQL.Add(' OR  Grade='+QuotedStr('L'));
QResullts.SQL.Add(' OR Grade='+QuotedStr('P'));
QResullts.SQL.Add(' OR Grade='+QuotedStr('Q'));
QResullts.SQL.Add(' OR Grade='+QuotedStr('R'));
QResullts.SQL.Add(' OR Grade='+QuotedStr('T'));
QResullts.SQL.Add(' OR Grade='+QuotedStr('X')+')))))');
QResullts.Open;

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nickjfox

ASKER

No, my mistake, the code as last posted works fine. It was something above causing a problem.

Geert G

you will produce a lot of problems on the database this way.
use bind variables, or parameters !

next to that consider using ALT+mouse drag to select the sql text within the quotes:
(only works in advanced editors like in Delphi)

QResults.SQL.Text := 
  'SELECT * FROM ResultsTable    '+
  'WHERE (age<= :minage)         '+
  '  AND (passed > :minpass)     '+
  '  AND (pass_Type is not null) '+
  '  AND (Overwork is not null)  ';
  // rest of lines
QResults.Prepare;
QResults.ParamByName('minage').AsInteger := 18;
QResults.ParamByName('minpass').AsInteger := 0;
QResults.Open;

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8080_Diver

@Geert_Gruwez,
Actually, if this is done on the fly and prepared every time, it isn't going to matter a lot one way or the other.
If the SQL were set up in a T(ADO)Query component on a DataModule and prepared there so that it was sitting around waiting to be used or if it were set up outside of a loop and then the parameters set and the query executed multiple times within the loop, your method would be much more efficent.
In fact, if it were set up in a stored procedure, then that would be still more efficient.