MySQL數據可的delete、upate語句和常用函數
例如：把所有性別為空的數據刪除
mysql> delete from student where Gender is null;
例如：把ID為2,4的數據刪除
mysql> delete from student where ID in (2,4);
2、清空數據表，只留表結構
mysql> truncate table student;
3、修改數據
mysql> update student set Score=80 where Name="肖清華";
4、統計字符串的字節數length()，字符數char_length()
mysql> select * from student where char_length(Name)=3; //查詢Name是三個字的人，也可以使用以下方法
mysql> select * from student where Name like "___";
5、 查詢指定時間內的數據
mysql> create table member(
ID int unsigned not null auto_increment,
Account varchar(30) not null unique,
Pass varchar(32),
Regtime datetime,
primary key(ID)); //新創建一個測試表
mysql> insert into member values(null,"李四","123456","2018-03-08");
mysql> insert into member values(null,"王五","1234567","2018-02-08");
mysql> insert into member values(null,"趙六","1234557","2017-02-08");
mysql> insert into member values(null,"夏明","123457","2017-12-08"); //插入測試數據
要求：統計近五天內註冊的會員人數
mysql> select count(*) from member where Regtime between date_add(now(),interval -5 day) and now();
mysql> select * from member where Regtime between date_add(now(),interval -5 day) and now();
6、格式化輸出
mysql> select Account 賬號,date_format(Regtime,"%Y年%m月%d日") 註冊日期 from member;
7、查詢當前系統的時間戳，然後轉換成年月日格式
mysql> select unix_timestamp() 系統時間戳;
mysql> select from_unixtime(1520494242);
mysql> select date_format(from_unixtime(1520494242),"%Y年%m月%d日");
8、將字符串連接
mysql> select concat("年齡:",Age) from student;
mysql> select concat_ws("-","年齡",Age) from student; //也是字符的拼接，只不過在字符中間加上了“-”
9、重復輸出，比如輸出十個"#"
mysql> select repeat("#",10);
mysql> select space(10); //輸出十個空格
10、大小寫轉換
mysql> select upper(Name) from student where Name like "w%"; //upper把小寫字母轉換為大寫字母
mysql> select lower(Name) from student where Name like "w%"; //lower把大寫字母轉換為小寫字母
11、字符截取
mysql> select left(Name,1) from student; //left截取左邊第一個字符
mysql> select right(Address,3) from student; //right截取右邊的字符
mysql> select mid(Address,2) from student; //mid從第幾個字符開始截取，這裏的首字符是1
mysql> select mid(Address,1,3) from student; //從第幾個開始到第幾個結束
12、if函數使用
等級：90優秀，70良好，60及格，以下補考
mysql> select Name 姓名,Gender 性別,Score 成績,if(Score>=90,"優秀",if(Score>=70,"良好",if(Score>=60,"及格","補考"))) 等級 from student;
13、uuid()生成唯一字符串
mysql> select uuid(),length(uuid()); //並查看長度
14、格式化數字
mysql> select format(1000,2); //將顯示1000.00
15、將IP轉換為數字
mysql> select inet_aton("192.168.200.101");
16、將數字轉換為IP
mysql> select inet_ntoa("3232286821");
MySQL數據可的delete、upate語句和常用函數