In the last episode (Aug 26), Karl Larsen said:
I was working with my version 5 and made a couple of views which
are very useful. Looking in the db I was able to see the VIEW's saved
as TABLE :-)
What command did you run to determine this? SHOW TABLES does list
them but that's to be expected since views act like tables. SHOW
TABLE STATUS and selecting from information_schema.tables both clearly
distinguish tables from views.
This was a surprise and not sure if this is the expected result or
not. Then I did some SELECT that involved the VIEW and it does work a
lot like another TABLE, but it can and mine does take data from many
TABLE's into a VIEW.
You can write a SELECT or even another VIEW using a VIEW. But if
you keep track of the time used by a query, it starts to get too long
if you use a SELECT of a VIEW that has within it another VIEW.
Mysql's optimization of views is currently very rudimentary. If your
view is simple (adding a computed column, etc) it directly modifies
your query to match the view and runs it on the view's parent table.
Otherwise it has to create a temporary table containing the entire
view's contents and then run your query on that. Nested views using
temptables could certainly be very slow.
http://dev.mysql.com/doc/refman/5.0/en/create-view.html
http://dev.mysql.com/doc/refman/5.0/en/view-restrictions.html
--
Dan Nelson
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