Posted by Jo�o Morais on 07/28/07 09:24

Hi there guys,

My doubt is related to PHP and MySQL usage, and it's related to check
if performed queries are performed with success, since we know that:

[quote]
mysql_query() - Return Values:
For SELECT, SHOW, DESCRIBE, EXPLAIN and other statements returning
resultset, mysql_query() returns a resource on success, or FALSE on
error.
For other type of SQL statements, UPDATE, DELETE, DROP, etc,
mysql_query() returns TRUE on success or FALSE on error.
[/quote]

Each time we perform an sql query, we can check if it was performed
with success like this:

[code=php]
$result = mysql_query('sql query string');
if (!$result) echo mysql_error();
[/code]

If it fails, it will display the succeeded error.

Now that I gave an example, here are my doubts:

1. Should this procedure be done every time a query is done, or,
should we assume that 'SELECT' queries are always done with success if
sql syntax is correct?

2. If we have a lot of queries that depend on each other (See the next
example), imagine that query1 and query2 are made with success, but
query3 fails, I will have inconsistent data since, the update is made
on query2, but no delete will be made on query3 since it fails.
How can we avoid this?

[code=php]
$result1 = mysql_query('SELECT ...');
if (!$result1) {
echo mysql_error();
exit(0);
}

$result2 = mysql_query('UPDATE ... with data supplied from $result1');
if (!$result2) {
echo mysql_error();
exit(0);
}

$result3 = mysql_query('INSERT / UPDATE / DELETE ... with data
supplied from $result1');
if (!$result3) {
echo mysql_error();
exit(0);
}
[/code]

Hope you guys can understand my examples, if not, I'll try to explain
in a better way.

Thanks for your attention and spent time on reading this.

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