Re: [Qgis-user] Field calculator - converting string to int with possible NULL values

[David Strip]

To answer my own question -
My problem occurred in a layer that was joined to a csv file. I had "NULL" values where there was no matching join field, as one might expect.
But it turns out that the csv file had the string "null" in an otherwise integer column for missing entries. Thus, when I thought the field calculator was rejecting NULL values, it was actually rejecting the "null" string.

Sorry for the distraction.

On 5/14/2021 4:21 PM, David Strip wrote:

I have a string field I wish to convert to int. A small subset of the records contain NULL.
I tried the following in the field calculator:

case
when ("bb_usage" IS NULL) then 0
else to_int("bb_usage"")
end

When I look at the preview, the result is correct whether or not the field contains int or NULL. But when I try to run it, I get an error:
 
       

I also tried

case
when ("bb_usage" IS NULL) then 0
when  ("bb_usage" IS NULL) then to_int("bb_usage")
end

and get the same error.

I tried

if ("bb_usage" IS NULL, 0, to_int("bb_usage"))

same error.

I know there are workarounds, but why don't any of these work? Why does to_int get evaluated on the NULLs?

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