Updating one mysql table based on calculations using variables in another table

I'm trying to update one table based on values in another table. What's wrong with the following request? Error: Unknow开发者_JAVA技巧n column 'source.col3' in 'where clause'

UPDATE target 
  SET target.col1 = source.col1 * target.col2,
WHERE target.col3 = source.col3

Well, for one you're not specifying 'source' as a table anywhere.

MySQL actually supports multiple table update, so you could write your code as:

UPDATE target, source
   SET target.col1=source.col1*target.col2
 WHERE target.col3=source.col3

Now whether that would actually do what you want I can't tell without knowing more about your tables.