Sort by column ASC, but NULL values first?

Question

I need to sort a PostgreSQL table ascending by a date/time field, e.g. last_updated.

But that field is allowed to be empty or null and I want records wi

Answer 1

You can create a custom ORDER BY using a CASE statement.
The CASE statement checks for your condition and assigns to rows which meet that condition a lower value than that which is assigned to rows which do not meet the condition.
It's probably easiest to understand given an example:

  SELECT last_updated 
    FROM your_table 
ORDER BY CASE WHEN last_updated IS NULL THEN 0 ELSE 1 END, 
         last_updated ASC;