问题
I have a query with a where condition like so:
WHERE A.event_date BETWEEN B.start_date AND B.end_date
The complexity is that if B.start_date is NULL, it means from time immemorial, similarly B.end_date is NULL, it means the present. So I still want to select a row where A.event_date > B.start_date and B.end_date is NULL, for example.
The long-winded way to do this is
WHERE A.event_date BETWEEN B.start_date AND B.end_date
OR (A.event_date > B.start_date AND B.end_date IS NULL)
OR (B.start_date IS NULL AND A.event_date < B.end_date)
Is there a more elegant solution (especially since in one query I have multiple between condition like that)
回答1:
IFNULL might help out here:
WHERE A.event_date BETWEEN IFNULL(B.start_date,"1900-01-01")
AND IFNULL(B.end_date,now());
回答2:
The COALESCE() function will return the first non-null value in the parameter list. Give this a try:
WHERE A.event_date BETWEEN COALESCE(B.start_date,'1900-01-01') and COALESCE(B.end_date,CURRENT_TIMESTAMP)
回答3:
IF PERFORMANCE MATTERS...
When I saw the @tom-mac answer I said : nice solution, I need to test it, and after I saw the @mw-goodjava answer and I wanted to compare.
According to this test http://blogs.x2line.com/al/archive/2004/03/01/189.aspx, it seems to be better to use IFNULL() instead of COALESCE() function but the best is still to use WHERE ... OR ... IS NULL like this :
WHERE (A.event_date >= B.start_date OR B.start_date IS NULL)
AND (A.event_date <= B.end_date OR B.end_date IS NULL)
So the query is more complex and not using BETWEEN but finaly I will choose that solution.
来源：https://stackoverflow.com/questions/26164224/mysql-using-between-comparison-with-null