一 、SELECT语句关键字的定义顺序
SELECT DISTINCT <select_list>
FROM <left_table>
<join_type> JOIN <right_table>
ON <join_condition>
WHERE <where_condition>
GROUP BY <group_by_list>
HAVING <having_condition>
ORDER BY <order_by_condition>
LIMIT <limit_number>
二 、SELECT语句关键字的执行顺序
1 (7) SELECT
2 (8) DISTINCT <select_list>
3 (1) FROM <left_table>
4 (3) <join_type> JOIN <right_table>
5 (2) ON <join_condition>
6 (4) WHERE <where_condition>
7 (5) GROUP BY <group_by_list>
8 (6) HAVING <having_condition>
9 (9) ORDER BY <order_by_condition>
10 (10) LIMIT <limit_number>
三、 准备表和数据
1. 新建一个测试数据库TestDB;
create database TestDB;
2.创建测试表table1和table2;
CREATE TABLE table1
(
customer_id VARCHAR(10) NOT NULL,
city VARCHAR(10) NOT NULL,
PRIMARY KEY(customer_id)
)ENGINE=INNODB DEFAULT CHARSET=UTF8;
CREATE TABLE table2
(
order_id INT NOT NULL auto_increment,
customer_id VARCHAR(10),
PRIMARY KEY(order_id)
)ENGINE=INNODB DEFAULT CHARSET=UTF8;
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