MySQL

2022-12-05 11:40:36

基础

use DBname;选择数据库
set names utf8;设置字符集

语法

select 选择

select [distinct column_name...]|* 
from tableName 
where column_name [operator] value 
{[joiner column_nameX operator valueX]...}
group by column_nameY desc|asc;
operator:
=,<>,>,<,>=,<=,BETWEEN,LIKE,IN
joiner:
AND,OR

insert 插入

第一种：
INSERT INTO table_name
VALUES (value1,value2,value3,...);
第二种：
INSERT INTO table_name (column1,column2,column3,...)
VALUES (value1,value2,value3,...);

update 更新

UPDATE table_name
SET column1=value1,column2=value2,...
WHERE some_column=some_value;

delete 删除

DELETE FROM table_name
WHERE some_column=some_value;

其他

create 创建

• DATABASE

CREATE DATABASE dbname;

• TABLE

CREATE TABLE table_name
(
column_name1 data_type(size),
column_name2 data_type(size),
column_name3 data_type(size),
....
);

• INDEX

列值不唯一索引:
CREATE INDEX index_name
ON table_name (column_name);

添加索引
ALTER table tableName ADD INDEX indexName(columnName);

删除索引
DROP INDEX [indexName] ON mytable; 

展示索引
SHOW INDEX FROM table_name;

列值唯一索引:
CREATE UNIQUE INDEX index_name
ON table_name (column_name);

修改唯一索引
ALTER table table_name ADD UNIQUE [indexName] (username(length));

alter 变更

• TABLE

添加列:
ALTER TABLE table_name
ADD column_name datatype

删除列:
ALTER TABLE table_name
DROP COLUMN column_name

改变列的数据类型:
ALTER TABLE table_name
MODIFY COLUMN column_name datatype

添加主键
ALTER TABLE table_name ADD PRIMARY KEY (i);

修改主键
ALTER TABLE table_name MODIFY i INT NOT NULL;

删除主键
ALTER TABLE table_name DROP PRIMARY KEY;

drop 删除

• DATABASE

DROP DATABASE database_name;

• TABLE

删除表:
DROP TABLE table_name 

删除表内数据
TRUNCATE TABLE table_name

• INDEX

Oracle:
DROP INDEX index_name

MySQL:
ALTER TABLE table_name DROP INDEX index_name

高级

返回指定记录数

MySql:
    SELECT column_name(s)
    FROM table_name
    LIMIT number;
Oracle:
    SELECT column_name(s)
    FROM table_name
    WHERE ROWNUM <= number;

通配符

  • 通配符
描述
%
替代 0 个或多个字符
_
替代一个字符
[charlist]
字符列中的任何单一字符
[^charlist] 或 [!charlist]
不在字符列中的任何单一字符
  • 别名
方式一:
    SELECT column_name AS alias_name
    FROM table_name;
方式二:
    SELECT column_name(s)
    FROM table_name AS alias_name;
  • 连接
SQL INNER JOIN 语法
    SELECT column_name(s)
    FROM table1
    INNER JOIN table2
    ON table1.column_name=table2.column_name;
或：
    SELECT column_name(s)
    FROM table1
    JOIN table2
    ON table1.column_name=table2.column_name;
SQL LEFT JOIN 语法
    SELECT column_name(s)
    FROM table1
    LEFT JOIN table2
    ON table1.column_name=table2.column_name;
或：
    SELECT column_name(s)
    FROM table1
    LEFT OUTER JOIN table2
    ON table1.column_name=table2.column_name;
SQL RIGHT JOIN 语法
    SELECT column_name(s)
    FROM table1
    RIGHT JOIN table2
    ON table1.column_name=table2.column_name;
或：
    SELECT column_name(s)
    FROM table1
    RIGHT OUTER JOIN table2
    ON table1.column_name=table2.column_name;
SQL FULL OUTER JOIN 语法
    SELECT column_name(s)
    FROM table1
    FULL OUTER JOIN table2
    ON table1.column_name=table2.column_name;
SQL UNION 语法
    SELECT column_name(s) FROM table1
    UNION
    SELECT column_name(s) FROM table2;
SQL UNION ALL 语法
    SELECT column_name(s) FROM table1
    UNION ALL
    SELECT column_name(s) FROM table2;
SQL SELECT INTO  复制表
MySQL:
SQL INSERT INTO SELECT 语法以从一个表中复制所有的列插入到另一个已存在的表中：
INSERT INTO table2
SELECT * FROM table1;
只复制希望的列插入到另一个已存在的表中：
INSERT INTO table2
(column_name(s))
SELECT column_name(s)
FROM table1;
其他数据库:
我们可以复制所有的列插入到新表中：
SELECT *
INTO newtable [IN externaldb]
FROM table1;
只复制希望的列插入到新表中：
SELECT column_name(s)
INTO newtable [IN externaldb]
FROM table1;

约束

  • NOT NULL:指示某列不能存储 NULL 值
  • UNIQUEL:保证某列的每行必须有唯一的值
  • PRIMARY KEY:主键
  • FOREIGN KEY:外键
  • CHECK:保证列中的值符合指定的条件
  • DEFAULT规定没有给列赋值时的默认值
  • AUTO_INCREMENT:自动地创建主键字段的值
  • 试图创建：
CREATE VIEW view_name AS
SELECT column_name(s)
FROM table_name
WHERE condition
  • 更新：
CREATE OR REPLACE VIEW view_name AS
SELECT column_name(s)
FROM table_name
WHERE condition
  • 删除：
DROP VIEW view_name

函数

从列中取得的值，返回一个单一的值
• AVG() - 返回平均值
SELECT AVG(column_name) FROM table_name
• COUNT() - 返回行数
SELECT COUNT([distinct] column_name|*) FROM table_name;
• FIRST() - 返回第一个记录的值

MySQL:
    SELECT column_name FROM table_name
    ORDER BY column_name ASC
    LIMIT 1;
Oracle:
    SELECT column_name FROM table_name
    ORDER BY column_name ASC
    WHERE ROWNUM <=1;

• LAST() - 返回最后一个记录的值

MYSQL:
    SELECT column_name FROM table_name
    ORDER BY column_name DESC
    LIMIT 1;
Oracle:
    SELECT column_name FROM table_name
    ORDER BY column_name DESC
    WHERE ROWNUM <=1;

• MAX() - 返回最大值
SELECT MAX(column_name) FROM table_name;
• MIN() - 返回最小值
SELECT MIN(column_name) FROM table_name;
• SUM() - 返回总和
SELECT SUM(column_name) FROM table_name;
基于输入值，返回一个单一的值
• UCASE() - 将某个字段转换为大写

SQL UCASE() 语法
SELECT UCASE(column_name) FROM table_name;
用于 SQL Server 的语法
SELECT UPPER(column_name) FROM table_name;

• LCASE() - 将某个字段转换为小写

SQL LCASE() 语法
SELECT LCASE(column_name) FROM table_name;
用于 SQL Server 的语法
SELECT LOWER(column_name) FROM table_name;

• MID() - 从某个文本字段提取字符

MySql 中使用
SELECT MID(column_name,start[,length]) FROM table_name;

• SubString(字段，1，end) - 从某个文本字段提取字符
• LEN() - 返回某个文本字段的长度

SQL LEN() 语法
SELECT LEN(column_name) FROM table_name;
MySQL 中函数为 LENGTH():
SELECT LENGTH(column_name) FROM table_name;

• ROUND() - 对某个数值字段进行指定小数位数的四舍五入

SELECT ROUND(column_name,decimals) FROM table_name;

• NOW() - 返回当前的系统日期和时间

SELECT NOW() FROM table_name;

• FORMAT() - 格式化某个字段的显示方式

SELECT FORMAT(column_name,format) FROM table_name;
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