Oracle Join Venn Diagram

A popular way of understanding sql joins is to visualize them using venn diagrams so each example have corresponding venn diagram appropriate select statement and the result.

Oracle join venn diagram. A join is not strictly a set operation that can be described with venn diagrams. They re more accurate and visually more useful. However like the commenters to her post i found that the venn diagrams didn t quite match the sql join syntax reality in my testing. For each row in the t1 table the full outer join compares it with every row in the t2 table.

11 oct 2007 a visual explanation of sql joins. Since sql joins appear to be set based the use of venn diagrams to explain them seems at first blush to be a natural fit. The following query will return a result set that is desired from us and will answer the question. I thought oracle s documentation on joins was ok myself although it doesn t have a diagram to show a conceptual model of them.

A sql join is a method to retrieve data from two or more database tables. This article presents a basic overview of what data from a particular sql join will look like. Oracle right join the right join or right outer join is a reversed version of the left join. Looked ok to me.

Well data on a database is sets and joins are the joining of sets of data so joins on that data can be represented with venn diagrams. So if in doubt please use join diagrams rather than venn diagrams. I thought ligaya turmelle s post on sql joins was a great primer for novice developers. A join is always a cross product with a predicate and possibly a union to add additional rows to the outer join result.

If rows from both tables meet the join condition the full outer join includes columns of both rows in the result set we say that the row in t1 table matches with the row in the t2 table in this case. As shown in the venn diagram we need to matched rows of all tables. While these venn diagrams are certainly useful to understand and remember sql join syntax they re not entirely accurate because sql join is a special type of a cartesian product the cross join. The sql multiple joins approach will help us to join onlinecustomers orders and sales tables.