Here is only to explain the four parts, the simplest, most commonly used four parts.
1, trigger.
Definition: What is a trigger? In the SQL Server is a certain manner to trigger a certain condition to trigger a certain condition. The trigger is a special stored procedure. There are three common triggers: applied to INSERT, UPDATE, and DELETE events, respectively. (SQL Server 2000 defines new triggers, not mentioned here)
Why should I use a trigger? For example, two tables:
Create Table Student (- Student Table StudentId Int Primary Key, - Study No. ....)
Create Table BorrowRecord (- Student Borrowing Record Table BorrowRecord Int Id "
The functions used: 1. If I change the students' student number, I hope that his borrowing record is still related to this student (that is, change the student number of the borrowing record); 2. If the student has graduated I hope to delete his student number and delete its borrowing record. and many more.
This can be used at this time. For 1. Create a UPDATE trigger:
Create Trigger Trustudent On Student for Update As if Update (Studient) Begin
Update borrowrecord set studentid = i.studentid from BorrowRecord Br, Deleted D, Inserted I where br.studentid = D.studentID
End understands two temporary tables inside the trigger: deleted, inserted. Note that deleted and inserted indicate the table "old record" and "new record" of the trigger event. A UPDATE process can be seen as: generating a new record to the Inserted table, copy the old record to the deleted table, then delete the Student record and write a new record.
For 2, create a delete trigger Create Trigger trdstudent on student for delete as delete BorrowRecord from BorrowRecord Br, Delted D Where br.studentId = D.studentID
From these two examples we can see the key to the trigger: A.2 temporary table; b. Trigger mechanism. Here we only explain the simplest trigger. Complex rendering. In fact, I don't encourage the use of triggers. The initial design idea of the trigger has been replaced by the "Cascade"
