Check the type of a field in a query

Posted on 2006-07-05
Last Modified: 2010-08-05
I have several questions...

I'm trying to use a variable in a query similar to the following

Query1.SQL.Text :=  'SELECT name FROM Table WHERE Value = :MyVal';
Query1.ParamByName('MyVal').Value := EditBox.Text;

My problem is that if Value is an integer then my Query won't accept the value and will give me an error.  I'm not sure of the best solution to this I think I need to check the type of 'Value' and assign the variable MyVal a value based on the type.  Is there a way I can check the type of a particular field in a db?

I'm getting input from EditBoxes and using it similar to above for things that should be integers I only want to have users able to enter numeric data into the field or check whether what they entered is a number before I assign the value to my query is there a function that does this?

3) if Value above in part 1 is a string and the text in my EditBox contains apostrophes do I need to edit the field at all so that the Query doesn't directly interpret the apostrophes.  
Question by:ICPooreman
LVL 12

Accepted Solution

Ivanov_G earned 100 total points
Comment Utility
1) It was a long time ago when I used this, but I think there was something like:

2) use StrToInt() function in try-catch block, if it fails - then the input is not integer
You can also have a look at:

3) QuoteStr()

Assisted Solution

JeePeeTee earned 100 total points
Comment Utility
Try Query1.ParamBtName('YourValue').DataType ... Maybe you have to call Query1.Prepare;

Use Prepare to allocate resources for the query and to perform additional optimizations.

Assisted Solution

sun4sunday earned 150 total points
Comment Utility
You can use it like
QueryName with the field name  like
Query1FIELDNAME.Value := Edit1.Text;   But the field in that query should a field type which can hold the String values like String.

If you the value from the edit box is only numbers then you can use it like
Query1FIELDNAME.AsInteger := Edit1.Text;

put the code under editbox key press, it will allow only the numbers and backspace

procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
  if (Key in ['0'..'9', #8]) then  //#8 for backspace
  Key := #0;


Expert Comment

Comment Utility
Query1FIELDNAME.Value := Edit1.Text;
Query1FIELDNAME.AsString := Edit1.Text;

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LVL 27

Expert Comment

Comment Utility
setting the correct Type of a Parameter:

in case of using BDE -> use .AsString instead of .Value (some suggestions from other experts)
in Case of using ADO -> as JeePeeTee suggested: Query1.ParamByName('MyVal').DataType := ftString;

the last one, may applyable for BDE too

meikl ;-)

Expert Comment

Comment Utility
meikl, u r right.
you here  ?!?!?!?

I thought you are in Germany football Stadium to watch the Portugal Vs France
(>>i am working as software-developer and database-designer in a german-company. From your member profile



Author Comment

Comment Utility
Thanks this has been really helpful!

I think I'm set with part 2 and 3

I have most of what I need for part 1 too but have one more question.    

Query1.SQL.Text :=  'SELECT name FROM Table WHERE Value = :MyVal';

Query1.ParamByName('MyVal').DataType := ftString;
works for what I need it to do but if this is possible I would like to instead have it assign the datatype based on the field like below.
Query1.ParamByName('MyVal').DataType := Query1.FieldByName('Value').DataType;

I'm trying to write a function which will do all of the changes needed to MyVal no matter how many params are included, but need to extract the DataType MyVal is supposed to be first.  

My question is can I figure out what field a param is associated with without knowing the name of the Field?  Say I didn't know 'Value' was my field name is it possible to derive the DataType of the field name associated with the param MyVal.  
LVL 27

Assisted Solution

kretzschmar earned 150 total points
Comment Utility
>I thought you are in Germany football Stadium to watch the Portugal Vs

:-)) no no, a visit in a football Stadium is too expensive, additional
the Stadium is too far away (about 400 km) from me. i will look at the play at tv. well, germany has lost yesterday against italy. was a good and fair play, italy was the luckier team at the end.

>My question is can I figure out what field a param is associated with without
>knowing the name of the Field?  Say I didn't know 'Value' was my field
>name is it possible to derive the DataType of the field name associated with
>the param MyVal.  

not really, most treating the parameter as string will work (except for date-types and blob-types), because this will implicit converted by the database then.

Another possible would be to to execute the query forced with no result-set like
select * from atable where 0 = 1
after executing you can read out the datatype of the needed field
and execute your real query after setting the datatype for the parameter.

meikl ;-)

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