[SQL] INSERT ... SELECT problem in Mysql

[Evil Azrael]

Hi!

I was trying to port a solution from postgresql to mysql for a mysql
user. im often using INSERT ... SELECTS with the same table in the
INSERT and SELECT statments at the same time. In Postgres i used to
use the destination only in a Subquery with IN, but in Mysql i had to
join the table, but it didn´t work and threw this error :  INSERT TABLE 'dummy' isn't 
allowed in FROM table list
with this page explaining the error :
http://www.mysql.de/doc/en/INSERT_SELECT.html

I have a problem with this part in the text

The target table of the INSERT statement cannot appear in the FROM clause of the 
SELECT part of the query because it's forbidden in standard SQL to SELECT from the 
same table into which you are inserting. (The problem is that the SELECT possibly 
would find records that were inserted earlier during the same run. When using subquery 
clauses, the situation could easily be very confusing!)


Is that correct? PostgreSQL allows this which is very handy, but
breaks so some ANSI compliance. Can anyform that ANSI SQL doesn´t
allow this?


Thanx

Christoph Nelles

  

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Re: [SQL] INSERT ... SELECT problem in Mysql

[Evil Azrael]

Thanx for the fast answer. I already thought something about like
this and considered sending the question to the advocacy list instead
of the SQL list. I really like their docs since i´ve read about their
reasons against Foreign Keys *g*

One more point in favor for PostgreSQL :)

Christoph Nelles


Am Freitag, 4. Juli 2003 um 23:45 schrieben Sie:

TL> Evil Azrael <[EMAIL PROTECTED]> writes:
>> I have a problem with this part in the text
>> 
>> The target table of the INSERT statement cannot appear in the FROM
>> clause of the SELECT part of the query because it's forbidden in
>> standard SQL to SELECT from the same table into which you are
>> inserting.

TL> This is just MySQL's self-serving reading of the spec.  What SQL92
TL> actually says is (section 13.8)

TL>  1) The following restrictions apply for Intermediate SQL:

TL> a) The leaf generally underlying table of T shall not be gen-
TL>   erally contained in the  immediately
TL>   contained in the  except as the
TL>of a .

TL> SQL99 puts it a little differently:

TL>  Conformance Rules

TL>  1) Without Feature F781, "Self-referencing operations", no leaf
TL> generally underlying table of T shall be generally contained in
TL> the  immediately contained in the  columns and source> except as the  or
TL>  of a column reference.

TL> In other words, the behavior is perfectly standard, it's just not
TL> required for minimal SQL implementations to support it.

TL> What the standard behavior is is defined by this rule, earlier in the
TL> same section:

TL>  3) The  is effectively evaluated before inserting
TL> any rows into B.

TL> that is, the SELECT doesn't see any rows that are being inserted into
TL> the target table during the same command.  There would not be any need
TL> for that rule if selecting from the same table you're inserting into
TL> were flat-out forbidden, as the MySQL docs claim.

TL> regards, tom lane



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