USE db_name;
CREATE DATABASE school;Use school;CREATE TABLE `StuInfo` (`STU_ID` varchar(10) NOT NULL ,`STU_NAME` varchar(25) NOT NULL ,`STU_SEX` char(2) NULL ,`CLASS` var char(10) NULL ,PRIMARY KEY (`STU_ID`));ALTER TABLE `scoreinfo` ADD CONSTRAINT `SS` FOREIGN KEY (`STU_ID`) REFERENCES `StuInfo` (`STU_ID`);CREATE TABLE `NewTable` (`STU_ID` varchar(10) NOT NULL ,`Tea_ID` varchar(10) NOT NULL ,PRIMARY KEY (`STU_ID`, `Tea_ID`),CONSTRAINT `STS` FOREIGN KEY (`STU_ID`) REFERENCES `StuInfo` (`STU_ID`),CONSTRAINT `STT` FOREIGN KEY (`Tea_ID`) REFERENCES `TeaInfo` (`TEA_ID`));SELECTteainfo.TEA_NAME,stuinfo.STU_NAME,stuinfo.CLASSFROMstuinfo join stuandteaon stuinfo.STU_ID=stuandtea.STU_IDjoin teainfoon teainfo.TEA_ID=stuandtea.Tea_ID
age TINYINT UNSIGNED,(无符号整型,>0)
salary FLOAT(8,2) UNSIGNED
SHOW TABLES FROM db_name;
SELECT DATABASE();//当前数据库
SHOW COLUMNS FROM table_name
INSERT [INTO] table_name [(cloumn_name,..)] VALUES(val...);
id SMALLINT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
username VARCHAR(25) NOT NULL UNIQUE KEY,
sex ENUM('1','2','3') DEFAULT '3',
约束:
约束保证数据的完整性和一致性。
约束分为表级约束(两个字段以上)和列级约束(一个字段)
包括:NOT NULL,PRIMARY KEY,UNIEUQ KEY,DEFAULT,FOREIGN KEY(实现一对一,一对多)
default-storage-engine=INNODB
SHOW INDEXES FROM table_name
CASCADE:从父表删除或更新,子表会自动删除更新匹配的行
SET NULL:从父表删除或更新行,设置子表中外键列为null
FOREIGN KEY (id) REFERENCES table_name(id) ON DELETE CASCADE
RESTRICT 拒接对父表的删除或更新
ALTER TABLE table_name ADD [COLUNM] (col_name col_definition,...) [FIRST|AFTER col_name]
ALTER TABLE table_name DROP [COLUNM] col_name
ALTER TABLE table_name ADD [CONSTRAINT PK_symbol] PRIMARY KEY [index_type] (index_col_name,)
ALTER TABLE table_name ALTER [COLUNM] col_name SET DEFAULT