2007-12Dec-30

This text is not right

HackFox mentions this, but it's still annoying. Textboxes cannot be right aligned when using regular text. When you set the Alignment property to 1, you end up with a textbox that looks properly. Yet, as soon as the textbox receives the focus, the content moves to the left.

How much to the left directly depends on the maximum length of the value, either spelled out in the MaxLength property, or implicitly defined through the control source. Textboxes with a maximum length of 1 almost behave correctly. The text is right aligned when the control gets the focus. The longer the value can be, the more VFP shifts text to the left. If you have a control that can hold like 200 characters, you might end up only seeing the rightmost character when the textbox has focus.

Note to myself: It doesn't work. Don't waste your time trying to make it work.

2007-12Dec-17

HAVING gotcha

Without a GROPY BY clause HAVING operates similar to a WHERE clause, except that the filter operates on the result set:

Create Cursor curSrc (Fld1 I, Fld2 I)
Insert into curSrc values (1,1)
Insert into curSrc values (2,2)

Select Fld1, fld1+1 as Fld3 ;
  From curSrc ;
  having Fld3 = 2

In this sample the query only returns those records where expression "FLD1+1" results in 2. The ability to query fields in the result set is limited, though. You can only query field names that do not appear in one of the source tables. Rewriting the query like this gets you a different result. The only difference in the statement is that FLD3 is now named FLD2:

Select Fld1, fld1+1 as Fld2 ;
  From curSrc ;
  having fld2 = 2

FLD2 is only used an alias in the field list, yet the HAVING clause operates on curSrc.Fld2 instead of FLD2 from the result set. This can cause changes in program behaviour when you add a field to a table with the same name as a calculated column.

Once you aggregate the result set with GROUP BY, rules change slightly. Referring to the field name in the result set yields an error message, if a field with the same name exists in any of the source tables. In the following query, FLD1+1=2 works in the HAVING clause, FLD2=2 wouldn't:

Select Fld1, fld1+1 as Fld2 ;
  From curSrc ;
  group by 1,2 ;
  having fld1+1 = 2

The same query is valid if the field name does not exist in any of the source tables. The following query uses FLD3 instead of FLD2 as the field name:

Select Fld1, fld1+1 as Fld3 ;
  From curSrc ;
  group by 1,2 ;
  having fld3 = 2

This is a situation you might encounter when doing refactoring and renaming fields. Changing the local field name suddenly causes errors when you run the query.