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数据库系统原理与应用教程（039）—— MySQL 查询（一）：SELECT 命令的语法分析
2022-07-23 06:49:00 【睿思达DBA_WGX】
数据库系统原理与应用教程（039）—— MySQL 查询（一）：SELECT 命令的语法分析
目录
MySQL 使用 SELECT 语句查询所需的数据。查询是指根据使用需求，使用不同的查询方式从数据库中获取所需的数据， 查询是 MySQL 最重要的操作。
一、SELECT 语句的语法结构
SELECT 语句的语法格式如下：
SELECT DISTINCT
<列名或表达式列表>
FROM
<表名> <连接类型>
JOIN <表名> ON <连接条件>
WHERE
<筛选条件>
GROUP BY
<分组字段列表>
HAVING
<分组筛选条件>
ORDER BY
<排序字段>
LIMIT <m,n>;
/* 参数说明： （1）DISTINCT：消除重复行。 （2）<字段或表达式列表>：表示所要查询字段的名称，可以使用（*）表示所有字段，也可以使用列名构造表达式。 （3）<连接类型>：可以使用 inner join，left join，right join 分别表示内连接，左连接，右连接。 （4）<连接条件>：一般使用两个表中的相同列构造连接条件。进行连接运算的表通常具有一对多联系，连接条件通常使用子表的外键和父表的主键建立。 （5）<筛选条件>：限定查询数据必须满足该查询条件。 （6）<分组字段列表>：按照指定的字段分组。 （7）<分组筛选条件>：对分组进行筛选。 （8）<排序字段>：对查询结果进行排序，可以进行升序（ASC）和降序（DESC）排列，默认是升序。 （9）LIMIT <m,n>：分页显示数据。 */
二、准备查询所需的数据表
/* CREATE TABLE student( s_id char(5) primary key, s_name char(20), birth datetime, phone char(20), addr varchar(100) ); INSERT INTO student VALUES('S2011','张晓刚','1999-12-3','13163735775','信阳市'), ('S2012','刘小青','1999-10-11','13603732255','新乡市'), ('S2013','曹梦德','1998-2-13','13853735522','郑州市'), ('S2014','刘艳','1998-6-24','13623735335','郑州市'), ('S2015','刘岩','1999-7-6','13813735225','信阳市'), ('S2016','刘若非','2000-8-31','13683735533','开封市'), ('S2021','董雯花','2000-7-30','13533735564','开封市'), ('S2022','周华建','1999-5-25','13243735578','郑州市'), ('S2023','特朗普','1999-6-21','13343735588','新乡市'), ('S2024','奥巴马','2000-10-17','13843735885','信阳市'), ('S2025','周健华','2000-8-22','13788736655','开封市'), ('S2026','张学有','1998-7-6','13743735566','郑州市'), ('S2031','李明博','1999-10-26','13643732222','郑州市'), ('S2032','达芬奇','1999-12-31','13043731234','郑州市'); CREATE TABLE teacher( t_id char(5) primary key, t_name char(20), job_title char(20), phone char(20) ); INSERT INTO teacher VALUES('T8001','欧阳修','教授','13703735666'), ('T8002','华罗庚','教授','13703735888'), ('T8003','钟南山','教授','13703735675'), ('T8004','钱学森','教授','13703735638'), ('T8005','李白','副教授','13703735828'), ('T8006','孔子','教授','13703735457'), ('T8007','王安石','副教授','13703735369'); CREATE TABLE course( c_id char(4) primary key, c_name char(20), t_id char(5) ); INSERT INTO course VALUES('C101','古代文学','T8001'), ('C102','高等数学','T8002'), ('C103','线性代数','T8002'), ('C104','临床医学','T8003'), ('C105','传染病学','T8003'), ('C106','大学物理','T8004'), ('C107','诗歌欣赏','T8005'), ('C108','教育学','T8006'), ('C109','刑事诉讼法','T8007'), ('C110','经济法','T8007'); CREATE TABLE score( s_id char(5), c_id char(4), score int, primary key(s_id, c_id) ); INSERT INTO score VALUES('S2011','C102',84),('S2011','C105',90),('S2011','C106',79),('S2011','C109',65), ('S2012','C101',67),('S2012','C102',52),('S2012','C103',55),('S2012','C104',86), ('S2012','C105',87),('S2012','C106',64),('S2012','C107',62), ('S2012','C108',73),('S2012','C109',78),('S2012','C110',89), ('S2013','C102',97),('S2013','C103',68),('S2013','C104',66),('S2013','C105',68), ('S2014','C102',90),('S2014','C103',85),('S2014','C104',77),('S2014','C105',96), ('S2015','C101',69),('S2015','C102',66),('S2015','C103',88),('S2015','C104',69), ('S2015','C105',66),('S2015','C106',88),('S2015','C107',69), ('S2015','C108',66),('S2015','C109',88),('S2015','C110',69), ('S2016','C101',65),('S2016','C102',69),('S2016','C107',82),('S2016','C108',56), ('S2021','C102',72),('S2021','C103',90),('S2021','C104',90),('S2021','C105',57), ('S2022','C102',88),('S2022','C103',93),('S2022','C109',47),('S2022','C110',62), ('S2023','C102',68),('S2023','C103',86),('S2023','C109',56),('S2023','C110',91), ('S2024','C102',87),('S2024','C103',97),('S2024','C109',80),('S2024','C110',81), ('S2025','C102',61),('S2025','C105',62),('S2025','C106',87),('S2025','C109',82), ('S2026','C102',59),('S2026','C105',48),('S2026','C106',90),('S2026','C109',73); */
mysql> select * from student;
+-------+-----------+---------------------+-------------+-----------+
| s_id | s_name | birth | phone | addr |
+-------+-----------+---------------------+-------------+-----------+
| S2011 | 张晓刚 | 1999-12-03 00:00:00 | 13163735775 | 信阳市 |
| S2012 | 刘小青 | 1999-10-11 00:00:00 | 13603732255 | 新乡市 |
| S2013 | 曹梦德 | 1998-02-13 00:00:00 | 13853735522 | 郑州市 |
| S2014 | 刘艳 | 1998-06-24 00:00:00 | 13623735335 | 郑州市 |
| S2015 | 刘岩 | 1999-07-06 00:00:00 | 13813735225 | 信阳市 |
| S2016 | 刘若非 | 2000-08-31 00:00:00 | 13683735533 | 开封市 |
| S2021 | 董雯花 | 2000-07-30 00:00:00 | 13533735564 | 开封市 |
| S2022 | 周华建 | 1999-05-25 00:00:00 | 13243735578 | 郑州市 |
| S2023 | 特朗普 | 1999-06-21 00:00:00 | 13343735588 | 新乡市 |
| S2024 | 奥巴马 | 2000-10-17 00:00:00 | 13843735885 | 信阳市 |
| S2025 | 周健华 | 2000-08-22 00:00:00 | 13788736655 | 开封市 |
| S2026 | 张学有 | 1998-07-06 00:00:00 | 13743735566 | 郑州市 |
| S2031 | 李明博 | 1999-10-26 00:00:00 | 13643732222 | 郑州市 |
| S2032 | 达芬奇 | 1999-12-31 00:00:00 | 13043731234 | 郑州市 |
+-------+-----------+---------------------+-------------+-----------+
14 rows in set (0.00 sec)
mysql> select * from teacher;
+-------+-----------+-----------+-------------+
| t_id | t_name | job_title | phone |
+-------+-----------+-----------+-------------+
| T8001 | 欧阳修 | 教授 | 13703735666 |
| T8002 | 华罗庚 | 教授 | 13703735888 |
| T8003 | 钟南山 | 教授 | 13703735675 |
| T8004 | 钱学森 | 教授 | 13703735638 |
| T8005 | 李白 | 副教授 | 13703735828 |
| T8006 | 孔子 | 教授 | 13703735457 |
| T8007 | 王安石 | 副教授 | 13703735369 |
+-------+-----------+-----------+-------------+
7 rows in set (0.00 sec)
mysql> select * from course;
+------+-----------------+-------+
| c_id | c_name | t_id |
+------+-----------------+-------+
| C101 | 古代文学 | T8001 |
| C102 | 高等数学 | T8002 |
| C103 | 线性代数 | T8002 |
| C104 | 临床医学 | T8003 |
| C105 | 传染病学 | T8003 |
| C106 | 大学物理 | T8004 |
| C107 | 诗歌欣赏 | T8005 |
| C108 | 教育学 | T8006 |
| C109 | 刑事诉讼法 | T8007 |
| C110 | 经济法 | T8007 |
+------+-----------------+-------+
10 rows in set (0.00 sec)
mysql> select * from score;
+-------+------+-------+
| s_id | c_id | score |
+-------+------+-------+
| S2011 | C102 | 84 |
| S2011 | C105 | 90 |
| S2011 | C106 | 79 |
| S2011 | C109 | 65 |
| S2012 | C101 | 67 |
| S2012 | C102 | 52 |
| S2012 | C103 | 55 |
| S2012 | C104 | 86 |
| S2012 | C105 | 87 |
| S2012 | C106 | 64 |
| S2012 | C107 | 62 |
| S2012 | C108 | 73 |
| S2012 | C109 | 78 |
| S2012 | C110 | 89 |
| S2013 | C102 | 97 |
| S2013 | C103 | 68 |
| S2013 | C104 | 66 |
| S2013 | C105 | 68 |
| S2014 | C102 | 90 |
| S2014 | C103 | 85 |
| S2014 | C104 | 77 |
| S2014 | C105 | 96 |
| S2015 | C101 | 69 |
| S2015 | C102 | 66 |
| S2015 | C103 | 88 |
| S2015 | C104 | 69 |
| S2015 | C105 | 66 |
| S2015 | C106 | 88 |
| S2015 | C107 | 69 |
| S2015 | C108 | 66 |
| S2015 | C109 | 88 |
| S2015 | C110 | 69 |
| S2016 | C101 | 65 |
| S2016 | C102 | 69 |
| S2016 | C107 | 82 |
| S2016 | C108 | 56 |
| S2021 | C102 | 72 |
| S2021 | C103 | 90 |
| S2021 | C104 | 90 |
| S2021 | C105 | 57 |
| S2022 | C102 | 88 |
| S2022 | C103 | 93 |
| S2022 | C109 | 47 |
| S2022 | C110 | 62 |
| S2023 | C102 | 68 |
| S2023 | C103 | 86 |
| S2023 | C109 | 56 |
| S2023 | C110 | 91 |
| S2024 | C102 | 87 |
| S2024 | C103 | 97 |
| S2024 | C109 | 80 |
| S2024 | C110 | 81 |
| S2025 | C102 | 61 |
| S2025 | C105 | 62 |
| S2025 | C106 | 87 |
| S2025 | C109 | 82 |
| S2026 | C102 | 59 |
| S2026 | C105 | 48 |
| S2026 | C106 | 90 |
| S2026 | C109 | 73 |
+-------+------+-------+
60 rows in set (0.00 sec)
三、SELECT 语句的书写顺序与执行顺序
1、SELECT 语句的书写顺序
SELECT DISTINCT <列名或表达式列表>
FROM <table_name> [INNER|LEFT|RIGHT] JOIN <table_name>
ON <连接条件>
WHERE <筛选条件>
GROUP BY <分组字段或表达式>
HAVING <分组筛选条件>
WITH ROLLUP
ORDER BY <排序字段或表达式>
LIMIT [m,]n
如果书写顺序不对会提示书写错误（1064）：
-- order by 和 where 顺序不对
mysql> select * from student order by s_name where addr='郑州市';
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'where addr='郑州
市'' at line 1
-- where 和 from 顺序不对
mysql> select * where addr='郑州市' from student;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'where addr='郑州
市' from student' at line 1
-- where 和 group 顺序不对
mysql> select addr,count(*) from student group by addr where s_name like '张%';
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'where s_name like '张%'' at line 1
2、SELECT 语句的执行顺序
--（1）指定查询所使用的表
FROM <table_name> [INNER|LEFT|RIGHT] JOIN <table_name>
ON <连接条件>
--（2）指定筛选条件（WHERE 后面不能使用 SELECT 所指定的列的别名，因为此时 select 子句还没有执行）
WHERE <筛选条件>
--（3）对数据分组
GROUP BY <分组字段或表达式>
WITH ROLLUP
HAVING <分组筛选条件>
--（4）生成需要显示的列和表达式
SELECT <字段或表达式列表>
--（5）消除重复的数据行
DISTINCT
--（6）对查询结果排序
ORDER BY <排序字段或表达式>
LIMIT [m,]n
四、查询举例
1、基本用法
mysql> select s_id,s_name,year(now())-year(birth) age from student;
+-------+-----------+------+
| s_id | s_name | age |
+-------+-----------+------+
| S2011 | 张晓刚 | 23 |
| S2012 | 刘小青 | 23 |
| S2013 | 曹梦德 | 24 |
| S2014 | 刘艳 | 24 |
| S2015 | 刘岩 | 23 |
| S2016 | 刘若非 | 22 |
| S2021 | 董雯花 | 22 |
| S2022 | 周华建 | 23 |
| S2023 | 特朗普 | 23 |
| S2024 | 奥巴马 | 22 |
| S2025 | 周健华 | 22 |
| S2026 | 张学有 | 24 |
| S2031 | 李明博 | 23 |
| S2032 | 达芬奇 | 23 |
+-------+-----------+------+
14 rows in set (0.03 sec)
2、指定查询条件
mysql> select * from student where s_name like '张%';
+-------+-----------+---------------------+-------------+-----------+
| s_id | s_name | birth | phone | addr |
+-------+-----------+---------------------+-------------+-----------+
| S2011 | 张晓刚 | 1999-12-03 00:00:00 | 13163735775 | 信阳市 |
| S2026 | 张学有 | 1998-07-06 00:00:00 | 13743735566 | 郑州市 |
+-------+-----------+---------------------+-------------+-----------+
2 rows in set (0.02 sec)
3、连接查询
/* select s.s_id, s_name, c.c_id, c_name, score from student s join score sc on s.s_id = sc.s_id join course c on sc.c_id = c.c_id where score > 90; */
mysql> select s.s_id, s_name, c.c_id, c_name, score
-> from student s join score sc
-> on s.s_id = sc.s_id
-> join course c
-> on sc.c_id = c.c_id
-> where score > 90;
+-------+-----------+------+--------------+-------+
| s_id | s_name | c_id | c_name | score |
+-------+-----------+------+--------------+-------+
| S2013 | 曹梦德 | C102 | 高等数学 | 97 |
| S2014 | 刘艳 | C105 | 传染病学 | 96 |
| S2022 | 周华建 | C103 | 线性代数 | 93 |
| S2023 | 特朗普 | C110 | 经济法 | 91 |
| S2024 | 奥巴马 | C103 | 线性代数 | 97 |
+-------+-----------+------+--------------+-------+
5 rows in set (0.00 sec)
4、对查询结果进行排序
mysql> select * from student order by birth desc;
+-------+-----------+---------------------+-------------+-----------+
| s_id | s_name | birth | phone | addr |
+-------+-----------+---------------------+-------------+-----------+
| S2024 | 奥巴马 | 2000-10-17 00:00:00 | 13843735885 | 信阳市 |
| S2016 | 刘若非 | 2000-08-31 00:00:00 | 13683735533 | 开封市 |
| S2025 | 周健华 | 2000-08-22 00:00:00 | 13788736655 | 开封市 |
| S2021 | 董雯花 | 2000-07-30 00:00:00 | 13533735564 | 开封市 |
| S2032 | 达芬奇 | 1999-12-31 00:00:00 | 13043731234 | 郑州市 |
| S2011 | 张晓刚 | 1999-12-03 00:00:00 | 13163735775 | 信阳市 |
| S2031 | 李明博 | 1999-10-26 00:00:00 | 13643732222 | 郑州市 |
| S2012 | 刘小青 | 1999-10-11 00:00:00 | 13603732255 | 新乡市 |
| S2015 | 刘岩 | 1999-07-06 00:00:00 | 13813735225 | 信阳市 |
| S2023 | 特朗普 | 1999-06-21 00:00:00 | 13343735588 | 新乡市 |
| S2022 | 周华建 | 1999-05-25 00:00:00 | 13243735578 | 郑州市 |
| S2026 | 张学有 | 1998-07-06 00:00:00 | 13743735566 | 郑州市 |
| S2014 | 刘艳 | 1998-06-24 00:00:00 | 13623735335 | 郑州市 |
| S2013 | 曹梦德 | 1998-02-13 00:00:00 | 13853735522 | 郑州市 |
+-------+-----------+---------------------+-------------+-----------+
14 rows in set (0.00 sec)
5、分组查询
mysql> select addr,count(*) cnt from student group by addr;
+-----------+-----+
| addr | cnt |
+-----------+-----+
| 信阳市 | 3 |
| 开封市 | 3 |
| 新乡市 | 2 |
| 郑州市 | 6 |
+-----------+-----+
4 rows in set (0.00 sec)
-- 对分组进行筛选
mysql> select addr,count(*) cnt from student group by addr having cnt>2;
+-----------+-----+
| addr | cnt |
+-----------+-----+
| 信阳市 | 3 |
| 开封市 | 3 |
| 郑州市 | 6 |
+-----------+-----+
3 rows in set (0.00 sec)
6、分页查询
-- 取前三条记录
mysql> select * from student order by birth limit 3;
+-------+-----------+---------------------+-------------+-----------+
| s_id | s_name | birth | phone | addr |
+-------+-----------+---------------------+-------------+-----------+
| S2013 | 曹梦德 | 1998-02-13 00:00:00 | 13853735522 | 郑州市 |
| S2014 | 刘艳 | 1998-06-24 00:00:00 | 13623735335 | 郑州市 |
| S2026 | 张学有 | 1998-07-06 00:00:00 | 13743735566 | 郑州市 |
+-------+-----------+---------------------+-------------+-----------+
3 rows in set (0.00 sec)
-- 从第 4 条开始，取 2 条记录
mysql> select * from student order by birth limit 3,2;
+-------+-----------+---------------------+-------------+-----------+
| s_id | s_name | birth | phone | addr |
+-------+-----------+---------------------+-------------+-----------+
| S2022 | 周华建 | 1999-05-25 00:00:00 | 13243735578 | 郑州市 |
| S2023 | 特朗普 | 1999-06-21 00:00:00 | 13343735588 | 新乡市 |
+-------+-----------+---------------------+-------------+-----------+
2 rows in set (0.00 sec)
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