Summary of Mysql's add, delete, modify, query sql statements

Mysql combined with PHP usually involves adding, deleting, modifying, and checking. I believe most PHPers here are like me. They have been vomiting writing this. Although it is not too difficult, there is no doubt that it is very important. , PHP cannot do without these. Therefore, for most novices, they must master the most basic and important knowledge of PHP.

The following is some basic mysql knowledge that I have summarized, mainly for better reference and help other beginners in the future. At the same time, I can also record my own growth and write some slightly difficult ones. question.

#创建数据库 

CREATE DATABASE aa;

#删除数据库

DROP DATABASE aa;

表的操作
#创建表 create table 表名

CREATE TABLE study(

id INT PRIMARY KEY,

title CHAR(10) NOT NULL,

sex CHAR(4) NOT NULL

);

#删除表(drop table 表名)

DROP TABLE study

#在表格中插入数据（insert into 表名（属性） values(对应的值)）

INSERT INTO study(id,title,sex) VALUES(1,"张三","男");

#更新表格数据（update 表名 set 键=值,键=值 where 条件）注意：修改多个属性中间必须要用","隔开，其他的符号无效,而set只能写一个;
UPDATE studySET id=2 , title="a" WHERE id=1

#删除表中数据（delete from 表名 where 条件）

DELETE FROM study WHERE id=0;

#查看表中数据（select 查询的东西 from 表名 where 条件）

SELECT * FROM study WHERE id=1

SELECT * FROM study ORDER BY age DESC

#注意：order by 字段名 asc 为升序，order by 字段名 desc 为降序

#Mysql添加字段名(既列名)   （alter table 表名 add 列名 字段类型）

ALTER TABLE study  ADD tell CHAR(20)

ALTER TABLE study ADD address CHAR(50) AFTER sex

#删除列（alter table 表名 drop 列名）

ALTER TABLE study DROP address

#修改列属性（alter table 表名 change 需要修改的列名 修改后的列名 新列名字段类型）

ALTER TABLE study CHANGE telphone tel CHAR(20) DEFAULT "-"
ALTER TABLE study CHANGE tel
ALTER TABLE study RENAME stu简单函数

SELECT SUM(age) AS "总年龄" FROM  study
SELECT AVG(age) AS "平均年龄" FROM study
SELECT MAX(age) AS "最大年龄" FROM study
SELECT COUNT(id) AS "人数" FROM study(统计人数选择主键不然可为空的列会影响结果)

Group table content:

2005-05-09 wins

2005-05 -09 win

2005-05-09 lose

2005-05-09 lose

2005-05-10 win

2005-05-10 Negative

2005-05-10 Negative

<br/><span style="color: rgb(0, 0, 0);">如果要生成下列结果, 该如何写sql语句?<br/><br/>胜 负2005-05-09  2  22005-05-10  1  2</span><span style="color: #800080"><br/><br/></span><span style="color: #000000">SELECT DATA AS " ",SUM(result=&#39;胜&#39;) AS "胜" ,SUM(result=&#39;负&#39;) AS "负" FROM test1 GROUP BY DATA <br/><br/>Case when(case 属性=“” then “” end)　　　　　　</span>

<span style="color: #000000"><br/>写出由table1.table2得到table3的sql语句<span style="color: #ff9900"><br/></span><br/><img src="/static/imghw/default1.png"  data-src="https://img.php.cn/upload/article/000/000/001/1c521202747c8f7bfc220d18e6bfec7e-0.png"  class="lazy" alt=""/><img src="/static/imghw/default1.png"  data-src="https://img.php.cn/upload/article/000/000/001/1c521202747c8f7bfc220d18e6bfec7e-1.png"  class="lazy" alt=""/><br/><br/><img src="/static/imghw/default1.png"  data-src="https://img.php.cn/upload/article/000/000/001/861e73c9fbfabad696027626740bf9d0-2.png"  class="lazy" alt=""/></span><span   style="max-width:90%"> <br/></span>

) 
AS = THEN 业绩yj ELSE NULL END) AS = THEN 业绩yj ELSE NULL END) 

AS FROM table1 t1 LEFT JOIN table2 t2 ON t1.部门dep=

<span style="color: #000000">用一条SQL语句查询出每门课都大于80分的学生姓名(表名为score)
　　Select distinct(去重) name from score where name not in(<br/><br/>　　　　Select name from score where fenshu<=80<br/>　　　　<br/>　　);</span><span style="color: #000000"><span style="color: #ff0000"><br/><br/></span><span style="font-size: 16px; color: rgb(0, 0, 0);"><strong>Union all、union</strong></span>（下分别为t1.t1）<img src="/static/imghw/default1.png"  data-src="https://img.php.cn/upload/article/000/000/001/861e73c9fbfabad696027626740bf9d0-4.png"  class="lazy" alt=""/><img src="/static/imghw/default1.png"  data-src="https://img.php.cn/upload/article/000/000/001/861e73c9fbfabad696027626740bf9d0-5.png"  class="lazy" alt=""/> </span>

SELECT * FROM t1 UNION ALL SELECT * FROM t2 (不去除重复)===》t3

SELECT * FROM t1 UNION  SELECT * FROM t2 （去除重复）=====>t4

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