Mysql表,列,库增删改查问题小结

#创建数据库CREATE DATABASE mytest CHARACTER SET gbk#删除数据库DROP DATABASE mytest表的操作#创建表（create table 表名（columns））CREATE TABLE students(id INT PRIMARY KEY,NAME CHAR(10) NOT NULL,sex CHAR(4) NOT NULL);#删除表(drop table 表名)DROP TABLE students#在表格中插入数据（insert into 表名（属性） values(对应的值)）INSERT INTO students(id,NAME,sex) VALUES(1,"张三","男")#更新表格数据（update 表名 set 键=值,键=值 where 条件）中间要用“，”隔开，其他的无效  set只需写一个UPDATE students SET id=2 , NAME="a" WHERE id=1#删除表中数据（delete from 表名 where 条件）DELETE FROM students WHERE id=0#查看表中数据（select 查询的东西 from 表名 where 条件）SELECT * FROM students WHERE id=1SELECT * FROM students ORDER BY age DESC(order by升序，order by 列名 desc降序)列#添加列（alter table 表名 add 列名 字段类型）ALTER TABLE students ADD tel CHAR(20)ALTER TABLE students ADD address CHAR(50) AFTER sex#删除列（alter table 表名 drop 列名）ALTER TABLE students 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 stu CHANGE telphone tel CHAR(20) DEFAULT "-"ALTER TABLE students CHANGE telALTER TABLE students RENAME stu简单函数SELECT SUM(age) AS "总年龄" FROM studentsSELECT AVG(age) AS "平均年龄" FROM studentsSELECT MAX(age) AS "最大年龄" FROM studentsSELECT COUNT(id) AS "人数" FROM students(统计人数选择主键不然可为空的列会影响结果)分组表内容：2005-05-09 胜2005-05-09 胜2005-05-09 负2005-05-09 负2005-05-10 胜2005-05-10 负2005-05-10 负    　　　　如果要生成下列结果, 该如何写sql语句?      胜 负2005-05-09 2 22005-05-10 1 2SELECT DATA AS " ",SUM(result='胜') AS "胜" ,SUM(result='负') AS "负" FROM test1 GROUP BY DATA Case when(case 属性=“” then “” end)　　　　　　写出由table1.table2得到table3的sql语句 SELECT t1.部门dep,SUM(CASE WHEN 月份mon='一月份' THEN 业绩yj ELSE NULL END) AS '一月份',SUM(CASE WHEN 月份mon='二月份' THEN 业绩yj ELSE NULL END) AS '二月份',SUM(CASE WHEN 月份mon='三月份' THEN 业绩yj ELSE NULL END) AS '三月份' FROM table1 t1 LEFT JOIN table2 t2 ON t1.部门dep=t2.部门dep GROUP BY 部门dep左连接与右连接(left join 表名 on 连接语句)Left join与right join区别就是：左连接是以主表为主，显示所有内容，若连接的表没有与它对应的值则不显示或显示为null，右连接同理。内连接用一条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(　　　　Select name from score where fenshu<=80;　　);Union all、union（下分别为t1.t1）SELECT * FROM t1 UNION ALL SELECT * FROM t2 (不去除重复)===》t3SELECT * FROM t1 UNION SELECT * FROM t2  （去除重复）=====>t4（上分别为t3.t4）