Sql Join Using 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.

Sql join using venn diagram. First of all we will briefly describe them using venn diagram illustrations. Inner join and a left outer join table 1 table 3 table 2 select from table 1 t1 inner join table 2 t2 on t1 id t2 fk left outer join table 3 t3. To achieve this you use the left join and a where clause to exclude the rows from the right table. The other one is multiple joins.

Semi join similar to inner join with less duplication from table 2. Inner join returns the rows that match in both tables. 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. Sometimes you want to get only rows from the left table that do not exist in the right table.

The following venn diagram illustrates the left join. Inner left right and full. Select from table 1 t1 where exists select 1 from table 2t where t2 id t1 fk. Basic sql join types.

There are four basic types of sql joins. You might ask yourself how many different types of join exist in sql server. Each join type specifies how sql server uses data from one table to select rows in another table. 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.

I also hate using venn diagrams for explaning sql joins. A sql join is a method to retrieve data from two or more database tables. The set bag discrepancy is one of the reasons. The answer is there are four main types of joins that exist in sql server.

I thought ligaya turmelle s post on sql joins was a great primer for novice developers. It s using venn diagram to build a valid sql join with an explanation. Venn diagrams completely break for anything above 3 sets tables 2 joins and may confuse you more than actually explain things. The easiest and most intuitive way to explain the difference between these four types is by using a venn diagram which shows all possible logical relations between data sets.

Basic sql join types. 11 oct 2007 a visual explanation of sql joins. To get a complete meaningful set of data you need to query data from these tables by using joins.