Tutorial on principles and applications of database system (039) -- MySQL query (I): syntax analysis of select command

Database system principle and Application Tutorial （039）—— MySQL Inquire about （ One ）：SELECT Syntax analysis of commands

MySQL Use SELECT Statement to query the required data . Query refers to the use of demand , Use different query methods to obtain the required data from the database , Query is MySQL The most important operation .

One 、SELECT The grammatical structure of a sentence

SELECT The syntax format of the statement is as follows ：

SELECT DISTINCT
    < Column name or expression list >
FROM
    < Table name > < Connection type >
JOIN < Table name > ON < Connection condition >
WHERE
    < filter >
GROUP BY
    < Group field list >
HAVING
    < Group filter criteria >
ORDER BY
    < Sort field >
LIMIT <m,n>;

/*  Parameter description ： （1）DISTINCT： Eliminate duplicate lines . （2）< List of fields or expressions >： Indicates the name of the field to be queried , have access to （*） Represents all fields , You can also use column names to construct expressions . （3）< Connection type >： have access to  inner join,left join,right join  Respectively represents internal connection , Left connection , The right connection . （4）< Connection condition >： Generally, the same columns in two tables are used to construct connection conditions . Tables that perform join operations usually have one to many connections , Connection conditions are usually established by using the foreign key of the child table and the primary key of the parent table . （5）< filter >： The restricted query data must meet the query condition . （6）< Group field list >： Group according to the specified fields . （7）< Group filter criteria >： Filter the groups . （8）< Sort field >： Sort query results , Can be in ascending order （ASC） And descending （DESC） array , The default is ascending . （9）LIMIT <m,n>： Display data in pages . */

Two 、 Prepare the data table required for query

/* 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',' Zhang Xiaogang ','1999-12-3','13163735775',' Xinyang City '), ('S2012',' Liu Xiaoqing ','1999-10-11','13603732255',' Xinxiang City '), ('S2013',' Cao mengde ','1998-2-13','13853735522',' Zhengzhou city '), ('S2014',' Liu Yan ','1998-6-24','13623735335',' Zhengzhou city '), ('S2015',' Liu Yan ','1999-7-6','13813735225',' Xinyang City '), ('S2016',' Liu Ruofei ','2000-8-31','13683735533',' Kaifeng City '), ('S2021',' Dong Wenhua ','2000-7-30','13533735564',' Kaifeng City '), ('S2022',' Zhou Huajian ','1999-5-25','13243735578',' Zhengzhou city '), ('S2023',' trump ','1999-6-21','13343735588',' Xinxiang City '), ('S2024',' Obama ','2000-10-17','13843735885',' Xinyang City '), ('S2025',' Zhou Jianhua ','2000-8-22','13788736655',' Kaifeng City '), ('S2026',' Zhang Xueyou ','1998-7-6','13743735566',' Zhengzhou city '), ('S2031',' Lee Myung Bak ','1999-10-26','13643732222',' Zhengzhou city '), ('S2032',' Vinci ','1999-12-31','13043731234',' Zhengzhou city '); 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',' Ouyang xiu ',' professor ','13703735666'), ('T8002',' Hua Luogeng ',' professor ','13703735888'), ('T8003',' Zhong Nanshan ',' professor ','13703735675'), ('T8004',' Qian xuesen ',' professor ','13703735638'), ('T8005',' Li Bai ',' associate professor ','13703735828'), ('T8006',' Confucius ',' professor ','13703735457'), ('T8007',' Wang Anshi ',' associate professor ','13703735369'); CREATE TABLE course( c_id char(4) primary key, c_name char(20), t_id char(5) ); INSERT INTO course VALUES('C101',' Ancient literature ','T8001'), ('C102',' Advanced mathematics ','T8002'), ('C103',' linear algebra ','T8002'), ('C104',' Clinical medicine ','T8003'), ('C105',' Infectious diseases ','T8003'), ('C106',' College Physics ','T8004'), ('C107',' Poetry appreciation ','T8005'), ('C108',' pedagogy ','T8006'), ('C109',' criminal procedure law ','T8007'), ('C110',' economic law ','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 |  Zhang Xiaogang     | 1999-12-03 00:00:00 | 13163735775 |  Xinyang City     |
| S2012 |  Liu Xiaoqing     | 1999-10-11 00:00:00 | 13603732255 |  Xinxiang City     |
| S2013 |  Cao mengde     | 1998-02-13 00:00:00 | 13853735522 |  Zhengzhou city     |
| S2014 |  Liu Yan       | 1998-06-24 00:00:00 | 13623735335 |  Zhengzhou city     |
| S2015 |  Liu Yan       | 1999-07-06 00:00:00 | 13813735225 |  Xinyang City     |
| S2016 |  Liu Ruofei     | 2000-08-31 00:00:00 | 13683735533 |  Kaifeng City     |
| S2021 |  Dong Wenhua     | 2000-07-30 00:00:00 | 13533735564 |  Kaifeng City     |
| S2022 |  Zhou Huajian     | 1999-05-25 00:00:00 | 13243735578 |  Zhengzhou city     |
| S2023 |  trump     | 1999-06-21 00:00:00 | 13343735588 |  Xinxiang City     |
| S2024 |  Obama     | 2000-10-17 00:00:00 | 13843735885 |  Xinyang City     |
| S2025 |  Zhou Jianhua     | 2000-08-22 00:00:00 | 13788736655 |  Kaifeng City     |
| S2026 |  Zhang Xueyou     | 1998-07-06 00:00:00 | 13743735566 |  Zhengzhou city     |
| S2031 |  Lee Myung Bak     | 1999-10-26 00:00:00 | 13643732222 |  Zhengzhou city     |
| S2032 |  Vinci     | 1999-12-31 00:00:00 | 13043731234 |  Zhengzhou city     |
+-------+-----------+---------------------+-------------+-----------+
14 rows in set (0.00 sec)

mysql> select * from teacher;
+-------+-----------+-----------+-------------+
| t_id  | t_name    | job_title | phone       |
+-------+-----------+-----------+-------------+
| T8001 |  Ouyang xiu     |  professor       | 13703735666 |
| T8002 |  Hua Luogeng     |  professor       | 13703735888 |
| T8003 |  Zhong Nanshan     |  professor       | 13703735675 |
| T8004 |  Qian xuesen     |  professor       | 13703735638 |
| T8005 |  Li Bai       |  associate professor     | 13703735828 |
| T8006 |  Confucius       |  professor       | 13703735457 |
| T8007 |  Wang Anshi     |  associate professor     | 13703735369 |
+-------+-----------+-----------+-------------+
7 rows in set (0.00 sec)

mysql> select * from course;
+------+-----------------+-------+
| c_id | c_name          | t_id  |
+------+-----------------+-------+
| C101 |  Ancient literature         | T8001 |
| C102 |  Advanced mathematics         | T8002 |
| C103 |  linear algebra         | T8002 |
| C104 |  Clinical medicine         | T8003 |
| C105 |  Infectious diseases         | T8003 |
| C106 |  College Physics         | T8004 |
| C107 |  Poetry appreciation         | T8005 |
| C108 |  pedagogy           | T8006 |
| C109 |  criminal procedure law       | T8007 |
| C110 |  economic law           | 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)

3、 ... and 、SELECT The writing order and execution order of statements

1、SELECT The writing order of sentences

SELECT DISTINCT < Column name or expression list >
FROM <table_name> [INNER|LEFT|RIGHT] JOIN <table_name>
ON < Connection condition >
WHERE < filter >
GROUP BY < Group fields or expressions >
HAVING < Group filter criteria >
WITH ROLLUP
ORDER BY < Sort field or expression >
LIMIT [m,]n

If the writing order is wrong, it will prompt the wrong writing （1064）：

-- order by  and  where  Wrong order 
mysql> select * from student order by s_name where addr=' Zhengzhou city ';
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=' zhengzhou 
 City '' at line 1

-- where  and  from  Wrong order 
mysql> select * where addr=' Zhengzhou city ' 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=' zhengzhou 
 City ' from student' at line 1

-- where  and  group  Wrong order 
mysql> select addr,count(*) from student group by addr where s_name like ' Zhang %';
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 ' Zhang %'' at line 1

2、SELECT The order in which statements are executed

--（1） Specify the table used by the query 
FROM <table_name> [INNER|LEFT|RIGHT] JOIN <table_name>
ON < Connection condition >
--（2） Specify filter criteria （WHERE  Can't be used later  SELECT  Alias of the specified column , Because at this time  select  Clause has not been executed ）
WHERE < filter >
--（3） Grouping data 
GROUP BY < Group fields or expressions >
WITH ROLLUP
HAVING < Group filter criteria >
--（4） Generate the columns and expressions that need to be displayed 
SELECT < List of fields or expressions >
--（5） De duplicate data rows 
DISTINCT
--（6） Sort query results 
ORDER BY < Sort field or expression >
LIMIT [m,]n

Four 、 Query example

1、 Basic usage

mysql> select s_id,s_name,year(now())-year(birth) age from student;
+-------+-----------+------+
| s_id  | s_name    | age  |
+-------+-----------+------+
| S2011 |  Zhang Xiaogang     |   23 |
| S2012 |  Liu Xiaoqing     |   23 |
| S2013 |  Cao mengde     |   24 |
| S2014 |  Liu Yan       |   24 |
| S2015 |  Liu Yan       |   23 |
| S2016 |  Liu Ruofei     |   22 |
| S2021 |  Dong Wenhua     |   22 |
| S2022 |  Zhou Huajian     |   23 |
| S2023 |  trump     |   23 |
| S2024 |  Obama     |   22 |
| S2025 |  Zhou Jianhua     |   22 |
| S2026 |  Zhang Xueyou     |   24 |
| S2031 |  Lee Myung Bak     |   23 |
| S2032 |  Vinci     |   23 |
+-------+-----------+------+
14 rows in set (0.03 sec)

2、 Specify query criteria

mysql> select * from student where s_name like ' Zhang %';
+-------+-----------+---------------------+-------------+-----------+
| s_id  | s_name    | birth               | phone       | addr      |
+-------+-----------+---------------------+-------------+-----------+
| S2011 |  Zhang Xiaogang     | 1999-12-03 00:00:00 | 13163735775 |  Xinyang City     |
| S2026 |  Zhang Xueyou     | 1998-07-06 00:00:00 | 13743735566 |  Zhengzhou city     |
+-------+-----------+---------------------+-------------+-----------+
2 rows in set (0.02 sec)

3、 Link query

/* 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 |  Cao mengde     | C102 |  Advanced mathematics      |    97 |
| S2014 |  Liu Yan       | C105 |  Infectious diseases      |    96 |
| S2022 |  Zhou Huajian     | C103 |  linear algebra      |    93 |
| S2023 |  trump     | C110 |  economic law        |    91 |
| S2024 |  Obama     | C103 |  linear algebra      |    97 |
+-------+-----------+------+--------------+-------+
5 rows in set (0.00 sec)

4、 Sort query results

mysql> select * from student order by birth desc;
+-------+-----------+---------------------+-------------+-----------+
| s_id  | s_name    | birth               | phone       | addr      |
+-------+-----------+---------------------+-------------+-----------+
| S2024 |  Obama     | 2000-10-17 00:00:00 | 13843735885 |  Xinyang City     |
| S2016 |  Liu Ruofei     | 2000-08-31 00:00:00 | 13683735533 |  Kaifeng City     |
| S2025 |  Zhou Jianhua     | 2000-08-22 00:00:00 | 13788736655 |  Kaifeng City     |
| S2021 |  Dong Wenhua     | 2000-07-30 00:00:00 | 13533735564 |  Kaifeng City     |
| S2032 |  Vinci     | 1999-12-31 00:00:00 | 13043731234 |  Zhengzhou city     |
| S2011 |  Zhang Xiaogang     | 1999-12-03 00:00:00 | 13163735775 |  Xinyang City     |
| S2031 |  Lee Myung Bak     | 1999-10-26 00:00:00 | 13643732222 |  Zhengzhou city     |
| S2012 |  Liu Xiaoqing     | 1999-10-11 00:00:00 | 13603732255 |  Xinxiang City     |
| S2015 |  Liu Yan       | 1999-07-06 00:00:00 | 13813735225 |  Xinyang City     |
| S2023 |  trump     | 1999-06-21 00:00:00 | 13343735588 |  Xinxiang City     |
| S2022 |  Zhou Huajian     | 1999-05-25 00:00:00 | 13243735578 |  Zhengzhou city     |
| S2026 |  Zhang Xueyou     | 1998-07-06 00:00:00 | 13743735566 |  Zhengzhou city     |
| S2014 |  Liu Yan       | 1998-06-24 00:00:00 | 13623735335 |  Zhengzhou city     |
| S2013 |  Cao mengde     | 1998-02-13 00:00:00 | 13853735522 |  Zhengzhou city     |
+-------+-----------+---------------------+-------------+-----------+
14 rows in set (0.00 sec)

5、 Group query

mysql> select addr,count(*) cnt from student group by addr;
+-----------+-----+
| addr      | cnt |
+-----------+-----+
|  Xinyang City     |   3 |
|  Kaifeng City     |   3 |
|  Xinxiang City     |   2 |
|  Zhengzhou city     |   6 |
+-----------+-----+
4 rows in set (0.00 sec)

--  Filter the groups 
mysql> select addr,count(*) cnt from student group by addr having cnt>2;
+-----------+-----+
| addr      | cnt |
+-----------+-----+
|  Xinyang City     |   3 |
|  Kaifeng City     |   3 |
|  Zhengzhou city     |   6 |
+-----------+-----+
3 rows in set (0.00 sec)

6、 Paging query

--  Take the first three records 
mysql> select * from student order by birth limit 3;
+-------+-----------+---------------------+-------------+-----------+
| s_id  | s_name    | birth               | phone       | addr      |
+-------+-----------+---------------------+-------------+-----------+
| S2013 |  Cao mengde     | 1998-02-13 00:00:00 | 13853735522 |  Zhengzhou city     |
| S2014 |  Liu Yan       | 1998-06-24 00:00:00 | 13623735335 |  Zhengzhou city     |
| S2026 |  Zhang Xueyou     | 1998-07-06 00:00:00 | 13743735566 |  Zhengzhou city     |
+-------+-----------+---------------------+-------------+-----------+
3 rows in set (0.00 sec)

--  From  4  Bar start , take  2  Bar record 
mysql> select * from student order by birth limit 3,2;
+-------+-----------+---------------------+-------------+-----------+
| s_id  | s_name    | birth               | phone       | addr      |
+-------+-----------+---------------------+-------------+-----------+
| S2022 |  Zhou Huajian     | 1999-05-25 00:00:00 | 13243735578 |  Zhengzhou city     |
| S2023 |  trump     | 1999-06-21 00:00:00 | 13343735588 |  Xinxiang City     |
+-------+-----------+---------------------+-------------+-----------+
2 rows in set (0.00 sec)