Question

Why doesn’t this work?

SELECT `user_log`.`COMPUTER_NAME`, `user_log`.`LOCATION` 
FROM `user_log`, `user_log_max` as max
WHERE max.`USER_NAME` = `user_log`.`USER_NAME` AND max.`ACCESS_DATE_TIME` = `user_log`.`ACCESS_DATE_TIME`

I get the following error:

#1054 - Unknown column 'max.ACCESS_DATE_TIME' in 'where clause'

I have tried taking out the alias:

SELECT `user_log`.`COMPUTER_NAME`, `user_log`.`LOCATION` 
FROM `user_log`, `user_log_max`
WHERE `user_log_max`.`USER_NAME` = `user_log`.`USER_NAME` AND `user_log_max`.`ACCESS_DATE_TIME` = `user_log`.`ACCESS_DATE_TIME`

and this error ->

#1054 - Unknown column 'user_log_max.ACCESS_DATE_TIME' in 'where clause'

It’s taking out the tick marks…why?

EDIT:

user_log_max:
USER_NAME        varchar(20)      
ACCESS_DATE_TIME timestamp  

user_log contains the same column, plus a few more including COMPUTER_NAME and LOCATION

user_log_max contains all the data from issuing this query on user_log

SELECT `USER_NAME`, MAX(`ACCESS_DATE_TIME`) FROM `user_log
GROUP BY `USER_NAME`

Essentially what I’m trying to do is select columns withing a MAX…GROUP BY other than what is in my GROUP BY.

EDIT 2:

Here is how I’m creating user_log_max ->

 CREATE TABLE `user_log_max`
SELECT `USER_NAME`, MAX(`ACCESS_DATE_TIME`) FROM `user_log`
GROUP BY `USER_NAME`

Answer 1

In your CREATE TABLE query, you must supply an alias for the MAX() aggregate column:

 CREATE TABLE `user_log_max`
   SELECT
     `USER_NAME`, 
      /* Alias this calculated value as ACCESS_DATE_TIME */
      MAX(`ACCESS_DATE_TIME`) AS `ACCESS_DATE_TIME` 
   FROM `user_log`
   GROUP BY `USER_NAME`

The way you had done it, the column name should be something like the whole string MAX(ACCESS_DATE_TIME), which is obviously very confusing.

Now, you can query it as you attempted to do:

/* The column ACCESS_DATE_TIME now exists in user_log_max, so this will work */
SELECT `user_log`.`COMPUTER_NAME`, `user_log`.`LOCATION` 
FROM `user_log`, `user_log_max`
WHERE `user_log_max`.`USER_NAME` = `user_log`.`USER_NAME` AND `user_log_max`.`ACCESS_DATE_TIME` = `user_log`.`ACCESS_DATE_TIME`