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mySQL - if...else condition help....

 
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mySQL - if...else condition help....
cancer10
post 18 Aug, 2008 - 08:39 AM
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Hi there,


I have a table - mytable and the columns in the table are as follows:


CityName (varchar)
updated_by (varchar)
added_by (varchar)

The first column is a city column, someone would add/update the city names and accordingly their name would be updated/added to the updated_by and added_by columns. Now, the condition of my query would be:

- if the updated_by column is NOT empty and the added_by column is empty, then the value of the updated_by would show .

- if the added_by column is NOT empty and the updated_by column is empty, then the value of the added_by column would show.

- if both added_by and updated_by columns are NOT empty then the value of the updated_by would show.



Could this be done in one single query? If yes, how (example plz)?


Thanx in advance
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mocker
post 18 Aug, 2008 - 09:09 AM
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mysql's if statement goes like

SELECT IF( (condition), (true), (false) ) fieldname

It looks kind of weird but its basically an if..else in one statement, or if you have used the (condition) ? true value : false value ; statement, it is like that.

I am going to assume you mean null when you say empty, in which case you'd want something like

SELECT IF( isnull(updated_by), added_by, updated_by) as person FROM table_name

If they are both null, then the value returned will be null anyways, otherwise it matches your conditions
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AdaHacker
post 18 Aug, 2008 - 04:13 PM
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If by "empty" you mean NULL, then a simpler and more ANSI-compatible way to do it would be the COALESCE function. It takes a list of arguments and returns the first one that isn't null.
SQL
SELECT COALESCE(updated_by, added_by) FROM yourtable;


If by "empty" you mean something else, then ANSI SQL defines (and MySQL implements) the CASE statement. You can use it for if-else style comparisons, such as:
SQL
SELECT CASE
WHEN updated_by = '' THEN added_by
WHEN added_by = '' THEN updated_by
ELSE updated_by
END FROM yourtable;
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