对于MySQL，第一种语法是错误的。第二种是MySQL的正确语法。请参阅此链接：https://www.w3schools.com...
“cannot delete or update a parent row: a foreign key”错误详解 1. 错误含义 “cannot delete or update a parent row: a foreign key”错误通常发生在数据库操作中,特别是在尝试删除或更新一个作为外键引用的父表记录时。这个错误表明,由于存在外键约束,你无法删除或更新父表中的相关记录,因为这些记录正在...
MySQL FOREIGN KEY ConstraintThe FOREIGN KEY constraint is used to prevent actions that would destroy links between tables.A FOREIGN KEY is a field (or collection of fields) in one table, that refers to the PRIMARY KEY in another table.
To create a FOREIGN KEY constraint on the "P_Id" column when the "Orders" table is already created, use the following SQL:MySQL / SQL Server / Oracle / MS Access:ALTER TABLE Orders ADD FOREIGN KEY (P_Id) REFERENCES Persons(P_Id)...
SQL FOREIGN KEY on ALTER TABLE To create aFOREIGN KEYconstraint on the "PersonID" column when the "Orders" table is already created, use the following SQL: MySQL / SQL Server / Oracle / MS Access: ALTERTABLEOrders ADDFOREIGNKEY(PersonID)REFERENCESPersons(PersonID); ...