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First of all, sorry, I couldn't phrase my question better.

So I want to be able to add a new column in my attributes table, say B, and it's value should be 1 if Column A's value is 1 and 0 if Column A's value is 2. in other words:

If A==1 : B=1

elif A==2 : B=2 I couldn't figure out a way to do this using Field Calculator.

Thanks Trying to update "MineDeleteIt" values based on path_type

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After the THEN it should be 'Bike lane baby' and also 'some arbitrary text'. You need single quotes for strings –  Nathan W Jan 23 '13 at 4:36
    
You are right. I had added double quotes and it didn't make any difference. Thanks a lot for your patience! –  Pep Jan 23 '13 at 4:39
1  
Double quotes are for column names. Single quotes for strings. –  Nathan W Jan 23 '13 at 4:43
    
@NathanW Sorry for pushing this, but do if-else conditions work too? I'm getting errors, but if it's possible I'll figure it out myself... –  Pep Jan 23 '13 at 4:50
1  
Not yet. We haven't added support yet. Feel free to open at ticket at hub.qgis.org and assign it to me. I'm the only Nathan in the list. –  Nathan W Jan 23 '13 at 5:07

1 Answer 1

up vote 2 down vote accepted

You can use a case statement to do that:

CASE 
    WHEN "A" = 1 THEN 1 
    WHEN "A" = 2 THEN 2 
END

If you want everything else to match you can use ELSE

CASE 
    WHEN "A" = 1 THEN 1 
    WHEN "A" = 2 THEN 2
    ELSE 0
END

This way everything that is not A=1 or A=2 will get assigned 0.

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thanks for your answer. Can you tell me where should I enter it though? should I use field Calculator? Because it says invalid expression... –  Pep Jan 22 '13 at 21:49
    
Which version of QGIS? –  Nathan W Jan 23 '13 at 0:35
    
it's 1.8. are u able to do it with field calculator? –  Pep Jan 23 '13 at 1:37
    
Yes. What does it say when you click (More INfo) –  Nathan W Jan 23 '13 at 3:56
    
it say's : Parser Error: syntax error, unexpected COLUMN_REF, expecting WHEN or ELSE or END Eval Error: No root node! Parsing failed? –  Pep Jan 23 '13 at 4:13

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