From: Frank
Date: December 22 2004 12:41am
Subject: About float fields
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I have a float field in a table and I'm experimenting some updates using =
a DataGrid and a MySqlCommanBuilder. If the field assumes some =
particular values (ie. 2.24) I get a concurrency error when I send the =
UPDATE query to the server.=20

After some research I found that this particular value is probably not =
handled with the exact value by the server on a float type field, =
because of the approximation applied by the system on loating point =
numbers which every programmer knows of (it's late night and I'm too =
lazy to try the math :-) ).

The problem is that the CommandBuilder creates the UPDATE command string =
including the value of the float field in the WHERE part (... WHERE =
'fld_1'=3D1 AND 'float_fld'=3D2.24). This causes the query to not find =
the row and then return 0 rows which cause the concurreny error in .NET. =


I noticed that changing the field type to double solves the problem, but =
I think this is a partial solution, because the operator '=3D' with a =
floating point number is always not recommended in comparisons. I think =
I should remove the floating field comparison from the command text (I =
read about concurrency settings for the command text, but don't remember =
where they are), but won't this cause problems in case of more than one =
user concurrently working on that record?
What is a 'best' practice to solve this problem?
Thanks,
Frank
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