MySQL connection query is easy to understand

Get ready ab Two tables , And insert data .

LEFT JOIN Left connection , Subject to the left table .（ To the left a The table shall prevail ,b Table without is automatically empty ）

RIGHT JOIN The right connection , Subject to the right table .（ With b The table shall prevail ,a Table without is automatically empty ）

 INNER JOIN Internal connection , Take the intersection of two tables .（ Take the intersection of two tables ）