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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nickjfoxAsked:
Who is Participating?
 
FactorBCommented:
Ups also after age there is ":=" instead "=" looks like Delphy/SQL hybrid, remove ":"

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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FactorBCommented:
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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8080_DiverCommented:
Essentially, you can follow the concept of using parentheses that you should have learned in your math classes.  Parentheses are a tool for clarification of the intent of the calculation (in this case, a boolean calculation).  So, any time when you either have concerns about the order in which things will happen or you want to force the order in which things happen, you can arrange the parentheses so that you can accomplish your goal.
On the other hand, the particular situation you are dealing with lends itself to the use of the IN clause, as is shown in the Delphi 2: code below.
However, one point to notice in the provided statements that will probably cause issues is the following line (as compared to the code I provide below):
Qresults.Active:=True;
 
That line should be:
Qresults.Active:=False;
 
There will also be problems from the lack of a space character between some of the elements in the SQL statement that is built with the other code offerings.  And, I would advise listing the columns that you are selecting rather than relying on the asterisk.  (That comes from the SQL Developer in me . . . using the SELECT * form is laible to cause you to retrieve a lot of unnecessary data from the columns that are in the table but not being used from the query. ;-)
 

Delphi 1:
 
if Qresults.Active then Qresults.Active:=False;
Qresults.SQL.Clear;
Qresults.SQL.Add('SELECT * ');
Qresults.SQL.Add('FROM   ResultsTable ');
Qresults.SQL.Add('WHERE  (age = ' + IntToStr(18));
Qresults.SQL.Add('  AND  ((Grade = ' + QuotedStr('A') + ' OR ');
Qresults.SQL.Add('        (Grade = ' + QuotedStr('B') + ' OR ');
Qresults.SQL.Add('        (Grade = ' + QuotedStr('C') + '))');
Qresults.Open;
 
Delphi 1:
 
if Qresults.Active then Qresults.Active:=False;
Qresults.SQL.Clear;
Qresults.SQL.Add('SELECT * ');
Qresults.SQL.Add('FROM   ResultsTable ');
Qresults.SQL.Add('WHERE  (age = ' + IntToStr(18));
Qresults.SQL.Add('  AND  (Grade IN (' + QuotedStr('A') + ', ');
Qresults.SQL.Add('                  QuotedStr('B') + ', ');
Qresults.SQL.Add('                  QuotedStr('C') + '))');
Qresults.Open;

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nickjfoxAuthor Commented:
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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nickjfoxAuthor Commented:
No, my mistake, the code as last posted works fine. It was something above causing a problem.
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Geert GOracle dbaCommented:
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_DiverCommented:
@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.
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