SQL Lesson 7: OUTER JOINs

Select query with LEFT/RIGHT/FULL JOINs on multiple tables
SELECT column, another_column, …
FROM mytable
INNER/LEFT/RIGHT/FULL JOIN another_table 
    ON mytable.id = another_table.matching_id
WHERE condition(s)
ORDER BY column, … ASC/DESC
LIMIT num_limit OFFSET num_offset;

a LEFT JOIN simply includes rows from A regardless of whether a matching row is found in B.

表示仅仅只是保留A 中的行数不管是否能找到B中

The RIGHT JOIN is the same, but reversed, keeping rows in B regardless of whether a match is found in A

仅仅保留B

 a FULL JOIN simply means that rows from both tables are kept, regardless of whether a matching row exists in the other table.

A&B 都保留