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From: "J.O. Aho" <user@example.net>
Newsgroups: alt.php.sql
Subject: Re: UPDATE Problem
Date: Thu, 1 Feb 2018 22:07:34 +0100
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On 02/01/18 21:07, Call Me Tom wrote:
> In table test there is a text field. For all rows I want to change the
> first 34 characters to something else. Here is my code.
> 
> <?php
> 
> require_once('./includes/mysql_connect.php');
> 
> $query = "SELECT report_id,fsacars_rep_url
>            FROM test";
> 
> $result=$dbh->query($query);
> $numin=$result->rowCount();
> echo "$numin";
> 
> while($url_orig=$result->FETCH(PDO::FETCH_NUM)) {
> 
>         $report_id = $url_orig[0];
>         $url_trim = substr($url_orig[1],34);
>         $url_new = 'http://localhost/CAA' . $url_trim;
> 
>         $sql="UPDATE test
>                 SET fsacars_rep_url = $url_new
>                 WHERE report_id = $report_id";        
>         $dbh->exec($sql);
>         
> } 
> 
> From tests I have shown that values are correct, However, the UPDATE
> fails. A response in a PHP forum was:
> 
> "You are updating the table before recovering all the rows from a row
> set.  The exec will invalidate the internal "cursor" that is used to
> fetch the rows one by one."
> 
> So, my question here is how do I change the first 34 characters of a
> field in every row of the table? 

Rewrite your SQL-query so that you do it all on the SQL-server instead
of doing it in the script.

See the following links to SQL-function
https://dev.mysql.com/doc/refman/5.7/en/string-functions.html#function_substr

https://dev.mysql.com/doc/refman/5.7/en/string-functions.html#function_trim

https://dev.mysql.com/doc/refman/5.7/en/string-functions.html#function_concat

Keep in mind, you still need to take care of results/errors for your
queries as Jerry already pointed out.


-- 

 //Aho