The join predicate serves to join tables. To join two columns from two tables, select the first column from the first table, hold down the mouse button and select the second column from the second table. A connecting line between the columns indicates that two tables are joined via two columns.
To specify the created join, select Joins or double-click on the connecting line that represents the join. Here you can see all existing joins, and enter the type and comparison operator for
a join. To delete a join, select Joins or double-click on the connecting line that represents the join and Delete, or press the 
key.
