In a loop, some queries succeed, other queries fail 'No database selected' - php

Question

I apply the same 2 queries to 3 tables, so just loop round and substitute the table names. The first INSERT query always works on test servers and on production. The second DELETE query works on two different test servers but is failing on production and throwing mysql error 1046 No database selected.
Affected code extract:
$queries = array(
"INSERT INTO knd_bkg.#table#
SELECT DISTINCT SQL_NO_CACHE
B.ASIN, Author, Title, EditorialReview, DetailPageURL, current_price, salesrank, number_reviews, erotica, G.BrowseNodeId, price_salesrank_checked_on
FROM bkd_books.club_books B
USE INDEX (free_quality)
RIGHT JOIN bkd_books.book_genre G on G.ASIN=B.ASIN
WHERE EXISTS
(
SELECT 1 FROM knd_bkg.genres K WHERE K.browsenode=G.BrowseNodeId
)
AND #priceWhere#
AND price_salesrank_checked_on > '#newerThan#'
AND B.number_reviews >= 4
AND B.rating >= 4.0
AND B.language = 'english'
AND B.hide_knd=0
AND B.public_domain=0;",
"DELETE T FROM knd_bkg.#table# T
INNER JOIN
(
SELECT N.* FROM knd_bkg.#table# N
INNER JOIN
(
SELECT DISTINCT ASIN, BrowseNodeId FROM knd_bkg.#table#
INNER JOIN knd_bkg.genres ON knd_bkg.genres.browsenode=knd_bkg.#table#.BrowseNodeId
WHERE isFiction=1
) F
ON F.ASIN=N.ASIN
INNER JOIN knd_bkg.genres
ON knd_bkg.genres.browsenode=N.BrowseNodeId
WHERE knd_bkg.genres.isNonFiction=1
) D
USING (ASIN, BrowseNodeId)
WHERE D.ASIN=T.ASIN AND D.BrowseNodeId=T.BrowseNodeId"
);
$tables = array(
"free_books" => array('priceWhere' => "B.current_price = 0", 'timePeriod' => $freeTimePeriod),
"99_books" => array('priceWhere' => "B.current_price > 0 AND B.current_price < 100", 'timePeriod' => $paidTimePeriod),
"399_books" => array('priceWhere' => "B.current_price >= 100 AND B.current_price < 400", 'timePeriod' => $paidTimePeriod),
);
connectSlaveDB();
foreach ($tables as $table => $data) {
$newerThan = date("Y-m-d H:i:s", strtotime("-" . $data['timePeriod'] . " hours"));
foreach ($queries as $query) {
$query = str_replace('#table#', $table, $query);
$query = str_replace('#newerThan#', $newerThan, $query);
$query = str_replace('#priceWhere#', $data['priceWhere'], $query);
Logger::_write(LOG_VERBOSE, "API - api/bkg/rebuild query: $query");
$result = mysql_query($query);
if (!$result) {
Logger::_write(LOG_ERR, "API - api/bkg/rebuild FAILED: " . mysql_error());
$success = false;
} else {
Logger::_write(LOG_VERBOSE, "API - api/bkg/rebuild SUCCESS");
}
}
}
And connectSlaveDB()
function connectSlaveDB()
{
global $dbSlave, $dbUser, $dbPass, $dbName;
$connSlave = mysql_connect($dbSlave, $dbUser, $dbPass, TRUE);
if (!$connSlave) {
Logger::_write(LOG_CRIT, "Unable to connect to slave DB");
include 'screens/error.inc.php';
exit();
}
mysql_set_charset('utf8', $connSlave);
mysql_select_db($dbName, $connSlave);
return TRUE;
}
The tables are MEMORY tables, but I get the same error with MYISAM, and only on production. This query is running on a replication slave and does not involve the master, but previous code TRUNCATES the tables so I don't believe it is down to permissions. When the query is taken out of the log file, it works fine in phpMyAdmin. And it's fine on the test servers.
I don't get the reason for the 1046 No database selected error. And after 3 hours I might be missing something really obvious. Especially as the failure pattern is like this, for one DB connection:
INSERT on free_books - success
DELETE on free_books - fail
INSERT on 99_books - success
DELETE on 99_books - fail
INSERT on 399_books - success
DELETE on 399_books - fail
Please excuse ugly globals and deprecated mysql* functions. This is a legacy app that is rather out of date. I know...

Answer 1

The syntax of your DELETE query may be causing the problem
DELETE T FROM
I know this has caused issues with UPDATE queries sometimes before due to a mysql bug.
Re-writing your query to avoid the T reference should resolve this issue.

Answer 2

Looks like the T alias in the DELETE was causing problems, but I'm not quiet sure why. The problem is now fixed by making the DELETE query to be:
"DELETE knd_bkg.#table# FROM knd_bkg.#table#
INNER JOIN
(
SELECT N.* FROM knd_bkg.#table# N
INNER JOIN
(
SELECT DISTINCT ASIN, BrowseNodeId FROM knd_bkg.#table#
INNER JOIN knd_bkg.genres ON knd_bkg.genres.browsenode=knd_bkg.#table#.BrowseNodeId
WHERE isFiction=1
) F
ON F.ASIN=N.ASIN
INNER JOIN knd_bkg.genres
ON knd_bkg.genres.browsenode=N.BrowseNodeId
WHERE knd_bkg.genres.isNonFiction=1
) D
USING (ASIN, BrowseNodeId)
WHERE D.ASIN=knd_bkg.#table#.ASIN AND D.BrowseNodeId=knd_bkg.#table#.BrowseNodeId"