using CASE for sorting

i am using MYSQL and i would like to "SELECT' a table and sort according to a numerical value that i either get it from "column1" or "column2", so:

***if a number from column1 exist, then this number is used to be sorted, otherwise the number from column2 (which always exists) is the number used to be sorted***

this is my current SQL statement:

PHP Code:

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SELECT * 
FROM table 
WHERE regtime >=DATE_SUB(NOW(), INTERVAL 20 DAY)
ORDER BY regtime ASC 


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i think i should use "CASE" but what i can do now is only sort in "column1" first if column1 IS NOT NULL, THEN sort in "column2"



i appreciate your help as this is already one of my last stages on my personal website :)

If it's a case of null or not null, you could do:

Code:

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SELECT *, IFNULL(column_1, column_2) AS sort_by_this
FROM table_name . . . ORDER BY sort_by_this

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awesome NogDog :D

never know the "AS" can do the trick!

thanks a million!