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Full Discussion: Optimizing query
Special Forums UNIX and Linux Applications Optimizing query Post 302130209 by kahuna on Friday 3rd of August 2007 02:31:24 PM
Old 08-03-2007
Quote:
Originally Posted by matrixmadhan
Basically, with combination of using selected columns ( column1 ) and the specific rowids ( rowid ), what is the need to specify an extra condition with a separate subquery to extract column1.
Yes you are right that it makes 2 sub-selects. If you have many duplicates, then your original post may be better. But suppose you only have a single duplicate. My subquery1 returns only a single value of column1 (the duplicate), where your subquery returns many values (the non duplicates). So now I have a single value to compare against tableA where you have many values. Yes, I still have to make subquery2, but it is against a much smaller set.

Subquery2 makes sure that, for a given value of column1, we don't delete the row with the smallest rowid.

Last edited by kahuna; 08-03-2007 at 04:03 PM.. Reason: Clarification
 

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MAXDB_AFFECTED_ROWS(3)							 1						    MAXDB_AFFECTED_ROWS(3)

maxdb_affected_rows - Gets the number of affected rows in a previous MaxDB operation

       Procedural style

SYNOPSIS
int maxdb_affected_rows (resource $link) DESCRIPTION
Object oriented style int$maxdb->affected_rows () maxdb_affected_rows(3) returns the number of rows affected by the last INSERT, UPDATE, or DELETE query associated with the provided $link parameter. If this number cannot be determined, this function will return -1. Note For SELECT statements maxdb_affected_rows(3) works like maxdb_num_rows(3). The maxdb_affected_rows(3) function only works with queries which modify a table. In order to return the number of rows from a SELECT query, use the maxdb_num_rows(3) function instead. RETURN VALUES
An integer greater than zero indicates the number of rows affected or retrieved. Zero indicates that no records where updated for an UPDATE statement, no rows matched the WHERE clause in the query or that no query has yet been executed. -1 indicates that the number of rows affected can not be determined. EXAMPLES
Example #1 Object oriented style <?php $maxdb = new maxdb("localhost", "MONA", "RED", "DEMODB"); /* check connection */ if (maxdb_connect_errno()) { printf("Connect failed: %s ", maxdb_connect_error()); exit(); } maxdb_report (MAXDB_REPORT_OFF); $maxdb->query("DROP TABLE mycustomer"); maxdb_report (MAXDB_REPORT_ERROR); /* Insert rows */ $maxdb->query("CREATE TABLE mycustomer AS SELECT * from hotel.customer"); printf("Affected rows (INSERT): %d ", $maxdb->affected_rows); $maxdb->query("ALTER TABLE mycustomer ADD Status int default 0"); /* update rows */ $maxdb->query("UPDATE mycustomer SET Status=1 WHERE cno > 50"); printf("Affected rows (UPDATE): %d ", $maxdb->affected_rows); /* delete rows */ $maxdb->query("DELETE FROM mycustomer WHERE cno < 50"); printf("Affected rows (DELETE): %d ", $maxdb->affected_rows); /* select all rows */ $result = $maxdb->query("SELECT title FROM mycustomer"); printf("Affected rows (SELECT): %d ", $maxdb->affected_rows); $result->close(); /* Delete table Language */ $maxdb->query("DROP TABLE mycustomer"); /* close connection */ $maxdb->close(); ?> Example #2 Procedural style <?php $link = maxdb_connect("localhost", "MONA", "RED", "DEMODB"); if (!$link) { printf("Can't connect to localhost. Error: %s ", maxdb_connect_error()); exit(); } maxdb_report (MAXDB_REPORT_OFF); maxdb_query($link,"DROP TABLE mycustomer"); maxdb_report (MAXDB_REPORT_ERROR); /* Insert rows */ maxdb_query($link, "CREATE TABLE mycustomer AS SELECT * from hotel.customer"); printf("Affected rows (INSERT): %d ", maxdb_affected_rows($link)); maxdb_query($link, "ALTER TABLE mycustomer ADD Status int default 0"); /* update rows */ maxdb_query($link, "UPDATE mycustomer SET Status=1 WHERE cno > 50"); printf("Affected rows (UPDATE): %d ", maxdb_affected_rows($link)); /* delete rows */ maxdb_query($link, "DELETE FROM mycustomer WHERE cno < 50"); printf("Affected rows (DELETE): %d ", maxdb_affected_rows($link)); /* select all rows */ $result = maxdb_query($link, "SELECT title FROM mycustomer"); printf("Affected rows (SELECT): %d ", maxdb_affected_rows($link)); maxdb_free_result($result); /* Delete table Language */ maxdb_query($link, "DROP TABLE mycustomer"); /* close connection */ maxdb_close($link); ?> The above example will output something similar to: Affected rows (INSERT): 15 Affected rows (UPDATE): 15 Affected rows (DELETE): 0 Affected rows (SELECT): 15 SEE ALSO
maxdb_num_rows(3), maxdb_info(3). PHP Documentation Group MAXDB_AFFECTED_ROWS(3)
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