Re: Truncate if exists

> For starters, the use-case hasn't been explained to my satisfaction.
> In what situation is it actually helpful to TRUNCATE a table that's
> not there yet?  Aren't you going to have to do a CREATE IF NOT EXISTS
> to keep from failing later in the script?  If so, why not just do that
> first?

There is a use case for the truncate 'mutliple' tables, maybe less clear for a single table.
Sébastien will speak here I suppose.

> Second, to my mind the point of a multi-table TRUNCATE is to ensure that
> all the referenced tables get reset to empty *together*.  With something
> like this, you'd have no such guarantee.  Consider a timeline like this:
> 
> 	Session 1			Session 2
> 
> 	TRUNCATE IF EXISTS a, b, c;
> 	... finds c doesn't exist ...
> 	... working on a and b ...
> 					CREATE TABLE c ( ... );
> 					INSERT INTO c ...;
> 	... commits ...
> 
> Now we have a, b, and c, but c isn't empty, violating the expectations
> of session 1.  So even if there's a use-case for IF EXISTS on a single
> table, I think it's very very dubious to allow it in multi-table
> commands.

well, in such case you probably don't want to use IF EXISTS.

-- 
Cédric Villemain +33 (0)6 20 30 22 52
http://2ndQuadrant.fr/
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