SQL Tuning Basic Overview 07-sql Joins

N years ago, just when the contact with SQL, is a multi-table query in a variety of internal connections, external connections, left outer connection, right outside the connection of a variety of connections to get dizzy.

What's more, there are two different ways to read the table connections in the book.

For example, the query for table A, table B

1, internal connection two kinds of wording:

SELECT * from A, B where a.id = b.id;

SELECT * from A join B on a.id = b.id;

2, right outer connection notation:

SELECT * from A, B where a.id (+) = b.id;

SELECT * from A right join B on a.id = b.id;

3, LEFT outer connection notation:

SELECT * from A, B where a.id = b.ID (+);

SELECT * from A LEFT join B on a.id = b.id;

The difference between the results of each query is really a painful memory.

Although this knowledge point seems to be easy to understand now, it has caused a lot of confusion for beginners.

And today just see a picture on the Internet, very good description of the different connections, very comprehensive, is the following picture.

I am not a developer, some of these connections I have not used so far, but when I see this diagram, the SQL joins is fully understood.

SQL Tuning Basic Overview 07-sql Joins