如何删除相关表的行

Question

I am new in database and in my application i want when i delete any project then deleted all tasks related to this project.Following is my table structure.I want to use this query in php. please help.Thanks in Advanced.

 Table:- Project
         -Project_ID (primary)
         -ProjectName

 Table:- Task
        -Task_ID ( primary)
        -project_ID
        -TaskName

Answer 1

referential integrity. check this web

This is the concept you are looking for "ON DELETE CASCADE".

Answer 2

You can design this in database itself ... It will delete in automatically

 ALTER TABLE `Task` ADD FOREIGN KEY ( `project_ID` ) REFERENCES `Project`.`project_ID` (
`project_ID`) ON DELETE CASCADE ON UPDATE CASCADE ;

Answer 3

first delete the records from table Task

then you can delete the records of table Project

example

suppose you want to delete the record from table Project which have Project_Id=3

do this in two steps

1. delete records from table Task which has foreign key of Porject_ID

   DELETE FROM Task WHERE Project_Id=3

2. then you can delete the record from table Project

   DELETE FROM Project WHERE Project_Id=3