MySQL database query basics, simple query, conditional query, sorting query results

1. SELECT statement SELECT COL1, COL2, ....COLn FROM TABLE1, TABLE2, ....TABLEn

[WHERE CONDITIONS] -- Query conditions

[GROUP BY GROUP_BY_LIST] -- Query result grouping

[HAVING CONDITIONS] -- Query conditions - statistical results as conditions

[ORDER BY ORDER_LIST[ASC|DESC] -- Query result sorting

2. Simple query

1. Query all rows and columns in the table

eg: Query all rows and columns in the player table

select user_qq,user_name,user_sex,user_birthday,user_mobile from users;

select * from users;

2. Query some columns of the table

eg: Query from the player table Player QQ and nickname

select user_qq,user_name from users;

3. Use of alias

eg: Query player QQ and nickname from the player table and display it as ' Player QQ' and 'player nickname'

select user_qq as 'player QQ',user_name as 'player nickname' from users;

select user_qq 'player QQ',user_name 'player nickname' from users;

4.DISTINCT keyword-eliminate duplicate rows in the result set

eg: Display QQ of players who participated in the game, and require players who participated in multiple games not to display QQ repeatedly

select distinct user_qq from scores;

5.LIMIT keyword-specify the display range of the data in the result set

eg: Display the 3rd to 5th data in the player table

select * from users limit 2,3;

select*from users limit 3 ---Only display the first three pieces of data

三.Conditional query

1. Ordinary condition query

Syntax: SELECT COL_LIST FROM TABLE_NAME [WHERE CONDITION_EXPRESSION]

eg1: Query the player information with QQ number 12301

select * from users where user_qq =12301;

eg2: Query data with scores greater than 2500

select *from scores where score>2500;

<> --- --Not equal to >= -----Greater than or equal to <= -----Less than or equal to

eg3: Query the score information of the game number 1 and the score is greater than 4000 points

select * from scores where gno=1 and score>4000;

Logical operators: and-- and

               or-- or

                                                   

#eg4: Query the score information of game numbers 1 and 2

select * from scores where gno=1 or gno=2;

2. Fuzzy query

eg1: Query scores with scores between 2500 (inclusive) and 3000 (inclusive)

select *from scores where score>=2500 and score<=3000;

select * from scores where score between 2500 and 3000;

eg2: Query score information where score is not between 2500 (inclusive) and 3000 (inclusive)

select * from scores where score not between 2500 and 3000;

eg3: Query players born from January 1, 1987 to July 31, 1992

select * from users where user_birthday between '1987-01-01' and '1992-0731';

Wildcard: '_' One character Branch like 'L_'

Any length Route_Code Like 'AMS-%'

[] Within the specified range Airbusno Like 'AB0[1-5 ] '

[^^] Not in parentheses, Airbusno Like' Ab0 [^] '

Eg4: ​​Query all the player information of all the surnames of the Sun

## Select * from users where user_name like 'Sun%';

eg5: Query the information of all players whose surname is not Sun

select * from users where user_name not like 'Sun%';

3. Query empty Value operator

eg: Query the information of players whose birthday is null

select * from users where use_birthday is null;

eg: Query the players whose birthday is not NULL Information

select * from users where user_birthday is not null;

Four pairs of query results sorting

1. Sort the specified column (sort by , sorting method)

Syntax: SELECT CLO_LIST FROM TABLE_NAME ORDER BY ORDER_BY_LIST [ASC/DESC]

Example: Query all score information numbered 1 in the score table, and sort by score in ascending order

select *from scores where gno=1 order by score asc.

Example: Query all score information numbered 1 in the score table, and sort by score in descending order

select * from score where gno=1 order by score desc.

2. Sort multiple columns (sorting basis, sorting method, priority)

Example: Query all information in the score table , and sort in ascending order of game number and descending order of score

select * from scores order by gno asc, score desc

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