SQL: If some rows in column returns null, then query again

Question

I need to join 2 tables together on the 'URL' column, however because of some crazy problems on our back-end, the URLs get logged inconsistently (slash/no-slash) in the two tables: http://google.com/ vs. http://google.com.

After I run my query to join, I get:

URL                     DATE
http://facebook.com     20130914
http://google.com/      NULL
http://youtube.com/     NULL

I'm a beginner with SQL, but does SQL have something like after you run a query, IF item in column is empty, then run query again?

I found How to ignore trailing slash while joining two string columns in SQL that I can then modify the 2nd query to remove trailing slash if exist.

What does your query look like? Why not join using rtrim(col,'/')? Not efficient, but probably more efficient than querying twice. — Barbara Laird
– Barbara Laird, Commented Oct 7, 2013 at 23:12
@BarbaraLaird: the reason is because I only want to rtrim if what it returned null on the first pass — user1899415
– user1899415, Commented Oct 7, 2013 at 23:32
SELECT DISTINCT b.url AS url, a.date AS date FROM url_results a LEFT OUTER JOIN url_samples b ON b.url = a.url; — user1899415
– user1899415, Commented Oct 8, 2013 at 0:02

cmd · Accepted Answer · 2013-10-07 23:17:46Z

1

Unfortunately, your best best course of action is to cleanup the data and normalize it on insert. The problem here is that you are performing a join with this data. Any work around will be very inefficient from a performance perspective.

answered Oct 7, 2013 at 23:17

cmd

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