1. Data Type

CHAR & VARCHAR

CHAR: fixed-length string
VARCHAR: variable-length string

ENUM & SET

ENUM: enumerated types, in a selected number of enumeration values
SET: set of multiple-choice

2. Keywords

LIKE

Keywords can be achieved LIKE fuzzy query, use wildcards% and _ on behalf of an unknown character
- %: Variable number of unspecified characters
- _: A character not specified

3. Statement

Sort --ORDER BY

SELECT name,age,salary,phone FROM employee ORDER BY salary DESC;

Aggregate Functions

SELECT MAX(salary) AS max_salary,MIN(salary) FROM employee;

4. Query

Subqueries

Want to know where the department is named "Tom" employees to do a few projects. Employee information is stored in the employee table, but the project engineering information stored in the table.
For such cases, we can use sub-query:

SELECT of_dpt,COUNT(proj_name) AS count_project FROM project GROUP BY of_dpt
HAVING of_dpt IN
(SELECT in_dpt FROM employee WHERE name='Tom');

Join query

SELECT id,name,people_num
FROM employee JOIN department
ON employee.in_dpt = department.dpt_name
ORDER BY id;

#另一种等价写法
SELECT id,name,people_num
FROM employee,department
WHERE employee.in_dpt = department.dpt_name
ORDER BY id;

5. Other

index

ALTER TABLE employee ADD INDEX idx_id (id);  #在employee表的id列上建立名为idx_id的索引

CREATE INDEX idx_name ON employee (name);   #在employee表的name列上建立名为idx_name的索引

view

#这里把视图当作一张表使用
CREATE VIEW v_emp (v_name,v_age,v_phone) AS SELECT name,age,phone FROM employee;

Import Data

LOAD DATA INFILE '文件路径和文件名' INTO TABLE 表名字;

Backup

mysqldump -u root 数据库名>备份文件名;   #备份整个数据库

mysqldump -u root 数据库名 表名字>备份文件名;  #备份整个表

restore

Combined with backup, restore backed up data to the database just

mysql -u root test < bak.sql

MySQL basis to fill a vacancy

1. Data Type

CHAR & VARCHAR

CHAR: fixed-length string

VARCHAR: variable-length string