数据库笔记2-数据表

表头:

查看当前数据库:SELECT DATABASE();

创建数据表:CREATE TABLE [IF NOT EXISTS] table_name (

colum_name(列名称) data_type(数据类型),

...

)#IF NOT EXISTS的作用是创建某个表时,存在这个表的话不会提示错误

例:CREATE TABLE tb1(

username VARCHAR(20),

age TINYINT UNSIGNED NOT NILL, #加'NOT NULL'后表示禁止为空

salary FLOAT(8,2) UNSIGNED

);

查看当前数据库的表:SHOW TABLES;

查看mysql数据库的表:SHOW TABLES FROM mysql;

查看数据表的结构:SHOW COLUMNS FROM tbl_name;

数据表中写入数据:INSERT [INTO] tbl_name [(col_name,...)] VALUES(val,...)

例:1.INSERT tb1 VALUES('Tom',25,7863.25);

2.INSERT tb1(username,salary) VALUES('John',4500.69);#只写入usernam,esalary的 值

记录查找:SELECT expr,... FROM tbl_name

例:SELECT * FROM tb1;

去重复：SELECT * FROM teacher GROUP BY depart

SELECT iid,iname FROM teacher GROUP BY isex