Table view of the database is the result of the operation.
Table in the database is the data unit;
a join operator;
It is an operational view of the result.
Database join explanation
1, join: the table structure is connected to a two view
2、left、right、inner：
Remove a record from a reference table into the (left, right) in the memory (the reference record)
3, on: the scanning condition according to the connection the connection table, there are matching records (matching records), the reference records matching records merged into one record, view into the connector;
Reference record needs to be connected all the matching records, the reference record may be recorded with a plurality of matching records to generate a plurality of views;
4, if the connection is no matching record is not included in the reference connector view recording; the other two ways connected credited view.
join operation is the database table, it is possible to cascade operation.
sql statement is as follows:
select * from A left join B
on A.aID = B.bID