Mysql select non empty column

If the mysql table for the 开发者_运维知识库gallery looks like:

    id     |    pic1    |   pic2    |    pic3    |     pic4    
 -------------------------------------------------------------
    1      |            |   b.jpg   |    c.jpg   |     d.jpg

How can I select the first non empty pic value from columns pic1, pic2, pic3, pic4 for the gallery with id=1?

In example above it will be value from the pic2 column (b.jpg)

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SELECT COALESCE(pic1, pic2, pic3, pic4, 'backup.gif') AS pic
FROM gallery
WHERE id = 1

backup.gif will be returned if all are empty. This also assumed that by empty the columns are NULL.

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SELECT COALESCE( pic1, pic2, pic3, pic4 ) AS pic
FROM gallery
WHERE id = 1;

Assuming you used NULL to represent an empty value, as opposed to blanks

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Would be interesting to understand why you are structuring your data in such an inflexible way in the database?