join the two tables which possess one to many relationship
The relationship appears to be between content_field_mem_id.field_mem_id_value and ex.mem_id
However, since content_field_mem_id.field_mem_id_value is an int and ex.mem_id is a varchar, you will need to cast/convert one of the columns as part of your join.  

It would be more reliable (although slower) to convert the int column to a varchar.

You didn't say which DB technology you are using, so I can't show the exact syntax for the convert (it is very different between MS SQL/Oracle/DB2/etc).