• MySQL必知必会

    文章目录

    SQL Tutorial
    Select

    查询

    SELECT column1, column2, ...
FROM table_name;

SELECT * FROM table_name;
    Select Distinct

    选择不同的项

    SELECT DISTINCT column1, column2, ...
FROM table_name;
    where

    范围选择

    SELECT column1, column2, ...
FROM table_name
WHERE condition;
    symboldescribe
    =Equal
    >Greater than
    <Less than
    >=Greater than or equal
    <=Less than or equal
    <>Not equal. Note: In some versions of SQL this operator may be written as !=
    BETWEENBetween a certain range
    LIKESearch for a pattern
    INTo specify multiple possible values for a column
    And、Or、Not

    与或非选择

    //与
SELECT column1, column2, ...
FROM table_name
WHERE condition1 AND condition2 AND condition3 ...;
//或
SELECT column1, column2, ...
FROM table_name
WHERE condition1 AND condition2 AND condition3 ...;
//非
SELECT column1, column2, ...
FROM table_name
WHERE NOT condition;
    Order By

    排序，默认升序，DESC：倒序

    SELECT column1, column2, ...
FROM table_name
ORDER BY column1, column2, ... ASC|DESC;
    Insert Into

    插入数据

    INSERT INTO table_name (column1, column2, column3, ...)
VALUES (value1, value2, value3, ...);

INSERT INTO table_name
VALUES (value1, value2, value3, ...);
    Null Value

    空值

    //寻找null value
SELECT column_names
FROM table_name
WHERE column_name IS NULL;
//寻找不为空
SELECT column_names
FROM table_name
WHERE column_name IS NULL;
    Update

    更新

    UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;
    Delete

    删除

    DELETE FROM table_name WHERE condition;
    Select Top

    选择指定数量的结果，不同数据库略有差异

    • SQL Server/MS Access : number
    • MySQL: Limit
    • Oracle：Rownum
    --SQL Server / MS Access Syntax:
SELECT TOP number|percent column_name(s)
FROM table_name
WHERE condition;

--MySQL Syntax:
SELECT column_name(s)
FROM table_name
WHERE condition
LIMIT number;

--Oracle Syntax:
SELECT column_name(s)
FROM table_name
WHERE ROWNUM <= number;
    Min和Max函数

    Min返回给定字段最小的一项数据，Max则相反

    SELECT MIN(column_name)
FROM table_name
WHERE condition;

SELECT MAX(column_name)
FROM table_name
WHERE condition;
    Count、Avg、Sum

    Count统计，Avg平均数、Sum求和

    --count
SELECT COUNT(column_name)
FROM table_name
WHERE condition;

--Avg
SELECT AVG(column_name)
FROM table_name
WHERE condition;

--Sum
SELECT SUM(column_name)
FROM table_name
WHERE condition;
    Like

    模糊查询

    • %：0个或多个字符
    • _ ：1个字符
    SELECT column1, column2, ...
FROM table_name
WHERE columnN LIKE pattern;
    WildCards

    通配符

    MS Access：

    符号描述例子
    *0个或多个字符bl* 可以代表 bl, black, blue, and blob
    ?代表一个字符h?t 可以代表hot, hat, and hit
    []代表方括号里的任意单个字符h[oa]t 可以代表 hot and hat, 但不能代表 hit
    !代表不在方括号里的任意字符h[!oa]t 与上面一个相反
    -代表一个范围c[a-b]t 代表 cat and cbt
    #代表任意一个数字2#5 代表205, 215, 225, 235, 245, 255, 265, 275, 285, 295

    SQL Server：

    符号描述例子
    %0个或多个字符bl* 可以代表 bl, black, blue, and blob
    _一个字符h_t 可以代表hot, hat, and hit
    []方括号里的任意字符h[oa]t 可以代表 hot and hat, 但不能代表 hit
    ^不在方括号里的任意字符h[^oa]t 代表 hit, 但不代表 hot 和 hat
    -代表一个范围c[a-b]t 代表 cat 和 cbt
    In

    相当于多个Or

    SELECT column_name(s)
FROM table_name
WHERE column_name IN (value1, value2, ...);
or
SELECT column_name(s)
FROM table_name
WHERE column_name IN (SELECT STATEMENT);
    Between

    指定选择范围

    SELECT column_name(s)
FROM table_name
WHERE column_name BETWEEN value1 AND value2;
    Alias

    别名

    --给字段取别名
SELECT column_name AS alias_name
FROM table_name;
--给表取别名
SELECT column_name(s)
FROM table_name AS alias_name;
    Join

    主要用于多表查询，不同的Join如下：

    1. Inner Join：返回表的交集部分

    在这里插入图片描述

    ```sql
SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column_name = table2.column_name;
```

    1. Left Join：返回左表全部和匹配的右表部分

      在这里插入图片描述

      SELECT column_name(s)
FROM table1
LEFT JOIN table2
ON table1.column_name = table2.column_name;

    2. Right Join：返回整个右表以及和左表匹配的部分

    在这里插入图片描述

    ```sql
SELECT column_name(s)
FROM table1
RIGHT JOIN table2
ON table1.column_name = table2.column_name;
```
    1. Full Join：返回两张表的所有匹配信息

    Full Join

    ```sql
SELECT column_name(s)
FROM table1
FULL OUTER JOIN table2
ON table1.column_name = table2.column_name
WHERE condition;
```

    1. Self Join：表与自身的联接

      SELECT column_name(s)
FROM table1 T1, table1 T2
WHERE condition;
    Union

    用于组合两个或多个结果集，但要求结果集合要有相同的结构和数据类型

    --默认不允许有重复
SELECT column_name(s) FROM table1
UNION
SELECT column_name(s) FROM table2;
--允许有重复
SELECT column_name(s) FROM table1
UNION ALL
SELECT column_name(s) FROM table2;
    Group By

    将结果指定字段进行分组，一般与聚合函数（COUNT, MAX, MIN, SUM, AVG）一起使用

    SELECT column_name(s)
FROM table_name
WHERE condition
GROUP BY column_name(s)
ORDER BY column_name(s);
    Having

    Having是为了解决Where无法使用聚合函数而引入的

    SELECT column_name(s)
FROM table_name
WHERE condition
GROUP BY column_name(s)
HAVING condition
ORDER BY column_name(s);
    Exists

    Exists用于测试子查询是否有结果，如果有，返回true。

    SELECT column_name(s)
FROM table_name
WHERE EXISTS
(SELECT column_name FROM table_name WHERE condition);
    Any、All

    Any、All主要用于Where和Having。当有任意子查询满足条件，Any返回true；All对应满足所有子查询。

    SELECT column_name(s)
FROM table_name
WHERE column_name operator ANY
(SELECT column_name FROM table_name WHERE condition);

SELECT column_name(s)
FROM table_name
WHERE column_name operator ALL
(SELECT column_name FROM table_name WHERE condition);
    Select Into

    Select Into主要用于将数据从一个表中复制到另外一个表中。通常用于备份

    --复制全部
SELECT *
INTO newtable [IN externaldb]
FROM oldtable
WHERE condition;
--复制部分
SELECT column1, column2, column3, ...
INTO newtable [IN externaldb]
FROM oldtable
WHERE condition;
    Insert Into Select

    Insert Into Select用于将一个表中的数据插入到另外一个表中去。注意要两个表要数据类型匹配

    INSERT INTO　target_table
SELECT * FROM source_table
WHERE condition;

INSERT INTO target_table (column1, column2, column3, ...)
SELECT column1, column2, column3, ...
FROM source_table
WHERE condition;
    Case

    Case用于多选择判断的情况

    CASE
    WHEN condition1 THEN result1
    WHEN condition2 THEN result2
    WHEN conditionN THEN resultN
    ELSE result
END;

eg.
SELECT OrderID, Quantity,
CASE
    WHEN Quantity > 30 THEN 'The quantity is greater than 30'
    WHEN Quantity = 30 THEN 'The quantity is 30'
    ELSE 'The quantity is under 30'
END AS QuantityText
FROM OrderDetails;
    NULL Functions

    用于判断是否为空，在某些时候需要将其设置成一个临时值

    eg.

    P_IdProductNameUnitPriceUnitsInStockUnitsOnOrder
    1Jarlsberg10.451615
    2Mascarpone32.5623
    3Gorgonzola15.67920
    --MySQL
SELECT ProductName, UnitPrice * (UnitsInStock + IFNULL(UnitsOnOrder, 0))
FROM Products;
SELECT ProductName, UnitPrice * (UnitsInStock + COALESCE(UnitsOnOrder, 0))
FROM Products;
--SQL Server
SELECT ProductName, UnitPrice * (UnitsInStock + ISNULL(UnitsOnOrder, 0))
FROM Products;
--MS Access
SELECT ProductName, UnitPrice * (UnitsInStock + IIF(IsNull(UnitsOnOrder), 0, UnitsOnOrder))
FROM Products;
--Oracle
SELECT ProductName, UnitPrice * (UnitsInStock + NVL(UnitsOnOrder, 0))
FROM Products;
    Stored Procedures

    Stored Procedures：存储过程也就是一段可编程函数，用于完成特定功能的SQL语句集和，使用存储过程主要有好处有

    • 提高效率:将重复度非常高的一些操作通过存储过程反复调用
    • 提高数据安全性：通过统一接口，从而提高数据的安全性

    存储过程创建、查看、删除

    delimiter $ ：该语句将sql语句的分隔符改为$(默认是;)从而确保多条sql语句能被放到一个存储过程中

    创建存储过程

    CREATE PROCEDURE 名称()
BEGIN
语句
END$

    调用存储过程

    CALL 名称();

    删除存储过程

    DROP PROCEDURE `存储过程名称`;
    Comments

    单行注释：–

    多行注释：/**/

    Operators

    运算符，SQL有各种各样的运算符，如算术运算符（±*/）、逻辑运算符（ALL AND OR）、位运算符（& | ^）等

    SQL DataBase
    Create DB

    创建数据库

    CREATE DATABASE databasename;
    Drop DB

    删除数据库

    DROP DATABASE databasename;
    Backup DB

    备份数据库

    --SQL Server
BACKUP DATABASE databasename
TO DISK = 'filepath';
    Create Table

    创建表

    CREATE TABLE table_name (
    column1 datatype,
    column2 datatype,
    column3 datatype,
   ....
);

--使用其他表来创建表
CREATE TABLE new_table_name AS
    SELECT column1, column2,...
    FROM existing_table_name
    WHERE ....;
    Drop Table

    删除表

    --表本身也删除
DROP TABLE table_name;
--只删除表的数据，表自身不删除
TRUNCATE TABLE table_name;
    Alter Table

    修改表结构，如增加字段、删除字段、修改字段等

    --添加字段
ALTER TABLE table_name
ADD column_name datatype;
--删除字段
ALTER TABLE table_name
ADD column_name datatype;
--修改字段
	--SQL Server/MS Access
	ALTER TABLE table_name
	ALTER COLUMN column_name datatype;
	--My SQL / Oracle
	ALTER TABLE table_name
	MODIFY COLUMN column_name datatype;
    Constraints

    表约束，一般在建表时给定相应约束

    CREATE TABLE table_name (
    column1 datatype constraint,
    column2 datatype constraint,
    column3 datatype constraint,
    ....
);

    ​ SQL常用约束：

    • NOT NULL：不为空

    • UNIQUE：值不同

    • PRIMARY KEY：主键约束

    • FORIGEN KEY：外键约束

    • CHECK：确保值满足特定条件

    • DEFAULT：给字段设置默认值

    • INDEX：用于快速从数据库创建和检索数据

      eg：

      --NOT NULL
CREATE TABLE Persons (
    ID int NOT NULL,
    LastName varchar(255) NOT NULL,
    FirstName varchar(255) NOT NULL,
    Age int
);
--Unique
	--SQL Server / Oracle / MS Access
	CREATE TABLE Persons (
    ID int NOT NULL,
    LastName varchar(255) NOT NULL,
    FirstName varchar(255) NOT NULL,
    Age int
	);
	--MySQL
	CREATE TABLE Persons (
    ID int NOT NULL,
    LastName varchar(255) NOT NULL,
    FirstName varchar(255),
    Age int,
    UNIQUE (ID)
	);
	--定义多个字段的组合约束unique
	CREATE TABLE Persons (
    ID int NOT NULL,
    LastName varchar(255) NOT NULL,
    FirstName varchar(255),
    Age int,
    CONSTRAINT UC_Person UNIQUE (ID,LastName)
	);
    Auto Increment

    自动增长：主要用于主键

    Dates

    日期：

    ​ MySQL：

    • DATE - format YYYY-MM-DD
    • DATETIME - format: YYYY-MM-DD HH:MI:SS
    • TIMESTAMP - format: YYYY-MM-DD HH:MI:SS
    • YEAR - format YYYY or YY

    ​ SQL Server：

    • DATE - format YYYY-MM-DD
    • DATETIME - format: YYYY-MM-DD HH:MI:SS
    • SMALLDATETIME - format: YYYY-MM-DD HH:MI:SS
    • TIMESTAMP - format: a unique number
    Views

    视图：基于结果集的虚拟表

    创建视图

    CREATE VIEW view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;

    更新视图

    CREATE OR REPLACE VIEW view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;

    删除视图

    DROP VIEW view_name;
    Injection

    注入：一种代码注入技术，可以侵入/破坏数据库，可以通过参数来防控

    Data Types

    数据类型：SQL有多种数据类型，一眼而言，主要分三类：字符串、数字、日期。具体参看官网

    MM-DD HH:MI:SS

    • TIMESTAMP - format: YYYY-MM-DD HH:MI:SS
    • YEAR - format YYYY or YY

    ​ SQL Server：

    • DATE - format YYYY-MM-DD
    • DATETIME - format: YYYY-MM-DD HH:MI:SS
    • SMALLDATETIME - format: YYYY-MM-DD HH:MI:SS
    • TIMESTAMP - format: a unique number
    Views

    视图：基于结果集的虚拟表

    创建视图

    CREATE VIEW view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;

    更新视图

    CREATE OR REPLACE VIEW view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;

    删除视图

    DROP VIEW view_name;
    Injection

    注入：一种代码注入技术，可以侵入/破坏数据库，可以通过参数来防控

    Data Types

    数据类型：SQL有多种数据类型，一眼而言，主要分三类：字符串、数字、日期。具体参看官网

    ​
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  • 原文地址：https://www.cnblogs.com/ma-liner/p/14196580.html
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