SQL php Select priority
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If I have 2 type of data in a table, which is either ID1 or ID2 empty, how can I select the rows that ID1 is not empty first , then follow by the data with ID2 not empty?

Example:

     Data | ID1 | ID2
 
     1    | ok  | 

     2    |     |  ok

     3    | ok  |



and returns:


    Data | ID1 | ID2

     1   | ok  | 

     3   | ok  |

     2   |     |  ok


Thank you very much.