Home/ Questions/Q 6079279
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-23T10:55:43+00:00

I created a database and two tables customer_full and customer_change through PhpMyAdmin. I successfully

  • 0

I created a database and two tables customer_full and customer_change through PhpMyAdmin. I successfully populated the two tables from two text files, the customer_full now contains 12902 rows while customer_change has 12947 rows, and each row has a CUSTOMER_ID field to identify each customer. The customer_change table has some new members that customer_full doesn’t, and I want to capture them.

The task now I need to do is very common, I need to get the rows that only exist in the customer_change table but not exist in the customer_full table, so I wrote and executed the following query:

SELECT * FROM customer_change 
LEFT JOIN customer_full ON customer_change.CUSTOMER_ID = customer_full.ID 
WHERE customer_full.ID IS NULL

It seems that after I submit the query in the PhpMyAdmin, it will always stay at “waiting for http://localhost/phpmyadmin/import.php” and finally turn out to be a time-out error.
However, if I run some simple query like 

SELECT * FROM customer_change,customer_full

It will work and returning the result by simply joining every record from two tables. So I am wondering could any experts help me debug, could it be my query has a effciency issue or should I do more checking on the configuration of the PhpMyAdmin? Or could there be any other possible reasons my previous query failed?

Please pardon me if this is simple since I just began self-learning MySql. Thanks in advance for all the help.

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    This: 

    SELECT * FROM customer_change,customer_full

    Is a cross-join it joins every row in table customer_change against every row in customer_full. So it returns 12,902 x 12,947 = 167,042,194 rows. No idea why you’d want this.

    The left join you’ve written looks correct:

    SELECT * FROM customer_change 
LEFT JOIN customer_full ON customer_change.CUSTOMER_ID = customer_full.ID 
WHERE customer_full.ID IS NULL

    Missing index
    In order for it to run quickly, you need to put an index on customer_change.CUSTOMER_ID and an index on customer_full.ID.
    Once you’ve done that it should run instantly.

    Corrupt tables
    There’s also a possibility that your tables are corrupt; esp. if you’re using MyISAM.
    Try and run the step outlined in this link:
    http://dev.mysql.com/doc/refman/5.0/en/corrupted-myisam-tables.html
    Or this link: http://www.thegeekstuff.com/2008/09/how-to-repair-corrupted-mysql-tables-using-myisamchk/

    • 0