Message-ID: <9e6f1c320511270949jca5a7dq710c4be8c017dc46@xxxxxxxxxxxxxx>
Date: Sun, 27 Nov 2005 12:49:17 -0500
From: Glenn Deschênes <maestroqc@xxxxxxxxx>
To: php-db@xxxxxxxxxxxxx
MIME-Version: 1.0
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Subject: Re: MySQL Update Quandry
This is not the problem.
The query fails when there is, as examples, an invalid syntax in the query
or the table is not found.
That's correct, and there's a distinct lack of
understanding going around the list.
A query may or may not return rows, and that is
not a sign of "failure". You might class it as
failing, but returning no rows is a sign that
there's no data matching your query - in which
case you may have no matching data, or you may
have written a valid query but one which doesn't ask the right question ;-)
So, checking mysql_error() return string will
only tell you if the query resulted in a database error.
It will not tell you if there were no results or changes to the database.
However, if the query executes but updates nothing. How can I know when the
update has changed a row or not? Not changing a row does not return a
failure.
PHP has functions for this, which you should read
in conjunction with the MySQL3.24 documentation
to understand when the DB considers a row inserted, deleted or updated.
mysql_affected_rows : http://us2.php.net/mysql-affected-rows
MySQL 4 and 5 have additional SQL statements to
get these values after the insert / update, using
a second query: SQL_CALC_FOUND_ROWS /
FOUND_ROWS(), LAST_INSERT_ID() LAST_INSERT_ID, ROW_COUNT()
For example, updating a row and giving it the
exact same values will result in an update row count of zero.
Inserting should always (unless the query fails)
give an affected_rows value more than zero.
Inserting *may* also result in a insert_id value
: *If* the table has a primary key, *and* it's an
autoincrement primary key, it'll return the
autoincrement value) : http://us2.php.net/mysql_insert_id
Matt's solutions works well. Since the application is hosted and I have
limited choices... the mysql_info() does the trick.
Although it's not the best use for flow control
for this task, because you have to parse the
string to get values from it (it's only available
PHP 4.3.0 onwards, which shouldn't be a problem
on this list), and it's not giving enough information unlike mysql_error()
HTH
Cheers - Neil
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