可以使用alert table或create index语给数据表加索引。mysql内部会把create index语句映射为alter table 操作。 alert table tab1_name add INDEX index_name alert table tab1_name add UNIQUE index_name alert table tab1_name add PRIMARY KEY (index_name) alert table tab1_name add FullTEXT index_name ...
Summary: in this tutorial, you will learn about MySQL foreign key and how to create, add, and drop foreign key constraints in MySQL. Introduction to MySQL foreign key# A foreign key is a field in a table that matches another field of another table. A foreign key places constraints on ...
29 ALTER TABLE files ADD CONSTRAINT files_users_fk FOREIGN KEY(`user_id`) REFERENCES users(`id`); 可以看出 files 依赖表users ,依赖表不能先删除。也就是说,需要先删除当前表,再删除外键关联表 我们来看看概念: 先看On Delete属性,可能取值为:No Action, Cascade,Set Null, Restrict属性。 当取值为No...
# dep_name 和 dep_location 数据会重复出现CREATETABLEemp(eidINTPRIMARYKEYAUTO_INCREMENT,enameVARCHAR(20),ageINT,dep_nameVARCHAR(20),dep_locationVARCHAR(20));--删除emp表,重新创建两张表DROPTABLEemp;# 主表,部门表。字段 id 为主键CREATETABLEdepartment(idINTPRIMARYKEYAUTO_INCREMENT,dep_nameVARCHAR(30...
WHERE TABLE_SCHEMA = 'luck'; 3. 禁用外键约束 在修改表结构前,临时禁用外键约束检查: SET FOREIGN_KEY_CHECKS = 0; 4. 修改数据库默认排序规则 将整个数据库的默认排序规则设置为 utf8mb4_0900_ai_ci(MySQL 8.0 默认): ALTER DATABASE luck CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci; ...
Bug #101270Error 1064: create table with foreign key Submitted:22 Oct 2020 4:39Modified:28 Oct 2020 11:00 Reporter:Dung NguyenEmail Updates: Status:DuplicateImpact on me: None Category:MySQL WorkbenchSeverity:S7 (Test Cases) Version:8.0.21OS:Windows (Microsoft Windows 10 Pro) ...
Create Table: CREATE TABLE`sakila_for_gbk`(`id`int(11)DEFAULT NULL,`name`varchar(45)DEFAULT NULL COMMENT'中文')ENGINE=InnoDB DEFAULTCHARSET=utf8# session character set: UTF-8# Description: Chinese character is invisible.echo"set names utf8; show create table sakila.sakila_for_gbk\G"|/usr...
-- 创建数据库 CREATE DATABASE school_db; -- 切换数据库 USE school_db; -- 创建表 CREATE TABLE students ( id INT PRIMARY KEY AUTO_INCREMENT, name VARCHAR(50) NOT NULL, age INT CHECK (age >= 10), class_id INT, FOREIGN KEY (class_id) REFERENCES classes(id) ); -- 修改表结构 ALTER...
I am creating two tables then doing an alter table to add a foreign key constraint and it gives the following error: Error Code: 1005. Can't create table 'mydb.#sql-870_16' (errno: 150) Here is a simple test to prove it:
ALTER TABLE <表名> DROP FOREIGN KEY <外键约束名>; (5)添加唯一约束的语法格式为: ALTER TABLE <表名> ADD CONSTRAINT <唯一约束名> UNIQUE(字段名); (6)删除唯一约束的语法格式为: ALTER TABLE <表名> DROP INDEX <唯一约束名>; 2.使用ALTER TABLE语句修改数据表 【任务实施】 操作演示 2.使用ALTER...