I keep getting "Data type mismatch in criteria expression" error in delphi - sql

Question

Whenever this code runs the I get the above error. The code is supposed to insert a record into a table and then delete records from another table.
for I := iMax - K to iMax do
begin
Inc(a);
with dmMenu.qryMcDonalds do
begin
SQL.Text :=
'SELECT ID, ItemID, ItemPrice, ItemCategory FROM tblCheckout WHERE ID = ' + IntToStr(I);
Open;
sItemID := Fields[1].AsString;
rItemPrice := Fields[2].AsFloat;
sItemCategory := Fields[3].AsString;
ShowMessage(IntToStr(I));
// I get the error here
SQL.Text :=
'INSERT INTO tblOrderItems (OrderItemID, OrderID, ItemID, ItemCategory, ItemPrice) VALUES ("' + sOrderID + '_' + IntToStr(a) + '"' + ', "' + sOrderID + '", "' + sItemID + '", "' + sItemCategory + '", "' + FloatToStrF(rItemPrice, ffCurrency, 10, 2) + '")';
ExecSQL;
SQL.Text := 'DELETE FROM tblCheckout WHERE ID = ' + IntToStr(I);
ExecSQL;
end; // with SQL
end; // for I
edit: I think i the problem is in the 'INSERT INTO' part. All the columns are short text except the last one, ItemPrice is a currency. I am also using Access

Answer 1

Please start a new project with just the following items on the main form:
A TAdoConnection configured to connect to your database;
A TAdoQuery configured to use the TAdoConnection
A TDataSource and TDBGrid configured to display the contents of the TAdoQuery.
Then, add the following code to the form
const
sSelect = 'select * from tblOrderItems';
sInsert = 'insert into tblOrderItems(OrderItemID, OrderID, ItemID, ItemCategory, ItemPrice) '#13#10
+ 'values(:OrderItemID, :OrderID, :ItemID, :ItemCategory, :ItemPrice)';
sOrderItemID = '0999';
sOrderID = '1999';
sItemID = '2999';
sItemCategory = 'Bolt';
fItemPrice = 5.99;
procedure TForm2.FormCreate(Sender: TObject);
begin
AdoQuery1.SQL.Text := sInsert;
AdoQuery1.Prepared := True;
AdoQuery1.Parameters.ParamByName('OrderItemID').Value:= sOrderItemID;
AdoQuery1.Parameters.ParamByName('OrderID').Value := sOrderID;
AdoQuery1.Parameters.ParamByName('ItemID').Value := sItemID;
AdoQuery1.Parameters.ParamByName('ItemCategory').Value := sItemCategory;
AdoQuery1.Parameters.ParamByName('ItemPrice').Value := fItemPrice;
AdoQuery1.ExecSQL;
AdoQuery1.SQL.Text := sSelect;
AdoQuery1.Open;
end;
Before compiling and running the program, review and change the values of the constants
so that they don't conflict with any rows already in your table.
The constant sInsert defines a so-called "parameterised SQL statement" Inside the Values
list, the items :OrderItemID, :OrderID, etc, are placeholders which the AdoQuery will turn into
parameters whose values you can supply at run-time, as in the block after AdoQuery1.Parameters.ParamByName(...
You should always construct SQL statements this way and not by concatenating strings
as your code attempts to do. It is far less error-prone, because it's easy to get into a
syntax muddle if you use DIY code and it also makes sure your queries are not prone
to Sql-Injection exploits, which they would be if you
give the user the opportunity to edit the SQL.
If you are using a FireDAC FDQuery, this has Params (an FD data-type) rather thn Parameters
but they work in pretty much the same way - see the Online Help.
In future, please be a bit more careful to ensure you include important details, especially things like the exact line where the error occurs - which you can check by single-stepping through your code using the debugger - and things like the exact db-access components you are using. Also try to get details right like whether a column is a "short text" type or an autonumber.
For a problem that needs to be debugged, like this one, you should also provide a complete, minimal, reproducible example, not just a snippet of code. Quite often, you will realise what the problem is while you are preparing the mre, so it helps you as well as us.

Answer 2

I bet the problem is in incompatible floating point format.
Use parameters to avoid it.