【添加/刪除數據表】
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ALTER TABLE users ADD age TINYINT UNSIGNED NOT NULL DEFAULT 10;//添加單列
ALTER TABLE users ADD password VARCHAR(30) NOT NULL AFTER username ;//添加有序單列
ALTER TABLE users ADD truename VARCHAR(30) NOT NULL FIRST ;//添加有序單列
ALTER TABLE users DROP truename; //刪除單列
ALTER TABLE users DROP password,DROP age; //刪除多列
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【添加/刪除約束】
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添加主鍵約束
CREATE TABLE users2(
username VARCHAR(20) NOT NULL,
pid SMALLINT UNSIGNED
);
爲新增ID添加主鍵約束:ALTER TABLE users2 ADD CONSTRAINT PK_users2_id PRIMARY KEY (id);
刪除主鍵約束:
ALTER TABLE users2 DROP PRIMARY KEY;
添加唯一約束
爲usename添加唯一約束:ALTER TABLE users2 ADD UNIQUE (username);刪除唯一約束前先查看,哪些字段有約束,刪除的是約束而不是字段!!!
SHOW INDEXES FROM users2;//查看索引
ALTER TABLE users2 DROP INDEX username;
添加外鍵約束
ALTER TABLE user2 ADD FOREIGN KEY (pid) REFERENCES provinces(id);
刪除外鍵約束,先查看:SHOW CREATE TABLE users2;
ALTER TABLE users2 DROP FOREIGN KEY users2_ibfk_1; //刪除之後,查看下
添加/刪除默認約束
ALTER TABLE users2 ALTER age SET DEFAULT 15;
刪除默認約束:
ALTER TABLE users2 ALTER age DROP DEFAULT;
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//添加唯一約束
ALTER TABLE getUserImage ADD UNIQUE (openID );
//修改數據表字段的名稱
alter table getUserImage change province region varchar(60);
//修改數據庫格式
alter database weixin_getUserImage character set utf8;
//修改數據表編碼
ALTER TABLE getUserImage DEFAULT CHARACTER SET utf8;
//該命令用於將表中字段的編碼方式改爲utf8
ALTER TABLE getUserImage CHANGE sex sex VARCHAR(10) CHARACTER SET utf8 NOT NULL;