MS Access – Number Format for VBA in Queries of Variant Type

ms accessvba

Lets say I have two queries like

select iif(condition, col, null) from table

select f(col) from table

where col is a double-valued column f is a VBA-public function(value as double) as variant. Somewhere later, I alter the format of the respective field to be displayed with a certain number format, for instance as a percentage. I have decided that f should be a variant since it is supposed to return Null if appropriate. However, in the former case, the format I specify is respected, but if I switch to the latter, the number format is totally ignored. Why?

Best Answer

The answer can be found here in Allen Browne's page:

in a query, a column can be only be ONE data type. JET therefore treats Variants as Text, since anything (numbers, dates, characters, ...) is valid in a Text column.

Numeric formatting options will not affect the text values which are automatically converted from the VBA Variant, even if the original value was coded as numeric.

His recommended solution is to do what you have already discovered: Use the IIF statement. The Jet engine uses datatype clues from the parameters to establish the returned column's data type.

Here's some code that will reveal the automatically-selected column type:

Dim rs As Recordset2
Set rs = CurrentDb.OpenRecordset("SELECT f([Col]) FROM table")
Debug.Print "Is text? " & (rs.Fields(0).Type = dbText)
rs.Close

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I think I can guess why your VBA is only changing around 150 records instead of all of them, but more importantly, you need to know that the specific method you're using--changing all the fields using VBA--can lead to incorrect data in your table. And, you can accomplish what you want much more easily with a SQL query ... even one made using the query designer. But for now I'll stick with plain SQL. There are three possibilities and corresponding approaches:

1 You just have to change a limited number of different sizes from mm to European. In that case use the switch function, e.g.:

update BS_2704
set Sizes = switch(
  Sizes = 150, 24
, Sizes = 160, 25
, ...
, Sizes = 325, 50
, true, Sizes
)

2 You can use a mathematical formula to convert from your mm size to your European measure, e.g. like http://en.wikipedia.org/wiki/Shoe_size#Europe:

update BS_2704
set Sizes = Sizes * 3 / 20

3 You can't use a mathematical formula, and you have such a large number of conversion mappings that putting them all in a single switch function is unwieldy: in this case you create a new table, e.g. named tblSizeMappings, with the mm sizes and the corresponding European sizes:

SizeMM SizeEuropean
   150           24
   160           25
   325           50

Then, do an update query like above but using the tblSizeMappings table to get the European sizes:

update BS_2704
inner join tblSizeMappings
on BS_2704.Sizes = tblSizeMappings.SizeMM
set BS_2704.Sizes = tblSizeMappings.SizeEuropean

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