MySQL Learning (ii)

Connection query:

1, connection above table 2, connection conditions

Left JOIN connection:

Select column 1, ... TableA left join TableB on tableA. Column = TableB. column where group by,having write as usual

[When connected to a large table, you can act as a table]

Slect goods_id, Goods.cat_is,cat_name,shop_price from goods left join category on goods.cat_id=category.cat_id

Right connection:

Select column 1, ... tableA right joins TableB on tableA. Column = TableB. Column where group By,having writes as usual

Internal connection:

Select column 1, ... tableA inner join TableB on tableA. Column = TableB. column where group by,having write as usual

The difference between left join, right connection and inner connection:

Left join: Take the left table as the quasi, go to the right table to find matching data, can not find matching with null;

Right connection: Whichever is the right table,

Internal connection: Query the left and right table data, that is, the part that does not have null.

Trigger: Trigger monitors a situation that triggers a certain action;

Trigger creation Syntax four elements: 1. Monitoring location (table) 2. Monitoring Events (Insert/update/delete) 3. Trigger Time (After/before) 4. Trigger Event (Insert/update/delete)

Transaction:

Open transaction Start transaction;

Execute SQL statement

Commit a transaction commit; /Roll back rollback;

MySQL Learning (ii)