Question

I keep getting this statement “Invalid use of group function”

for this query

 mysql_query("UPDATE users SET users.lastmessage = MAX(messages.id) WHERE users.name ='tom'") 
or die(mysql_error());  

What I’m trying to do is take the lastmessage field in the users table and update it to be the largest id in the messages table where the name = tom

What did I do incorrectly

Answer 1

You want to execute a sub-query to get the maximum Id for the user ‘tom’ which is done as follows:

UPDATE users 
   SET users.lastmessage = (SELECT MAX(id) FROM Messages WHERE messages.name = users.name) 
 WHERE users.Name = 'tom'

Edit: WHERE clause to only perform this for the correct user