SQL-Triggers-Page22

-

                                                                                              


👉What are Database Triggers?

Database triggers are procedures that are implicitly executed by the Oracle engine when an insert, update, or delete is issued against a table (from SQL editor or through an application). These procedures are called database triggers.

When a trigger is fired, a SQL statement inside the trigger's PL/SQL code block can also fire the same or some other trigger. This is called cascading trigger.

Difference between Triggers and Procedures:

1)Triggers do not accept parameters whereas Procedures can.
2)A trigger is executed implicitly by the Oracle engine itself upon modification of an associated table or its data. Whereas to execute a procedure, it has to be explicitly called by a user.

A trigger has three basic parts:
1)A triggering event or statement
2)A trigger restriction
3)A trigger action

✅Triggering Event:

It is a SQL statement that causes a trigger to be fired. It can be Insert, Update or Delete statement for a specific table.

✅Trigger Restriction:

A trigger restriction specifies a boolean expression that must be true for the trigger to fire.

✅Trigger Action:

A trigger action is the PL/SQL code to be executed when triggering statement is encountered and any trigger restriction evaluates to true.

Comments

Post a Comment

Popular posts from this blog

SQL-ForeignKeyConstraint-Page6

-
Image
                                                                              👉 Foreign Key Constraint Foreign Key represent relationships between tables. A foreign key is a column or group of columns whose values are derived from the primary key or unique key of some other table. ✅ The table in which the foreign key is defined is called Foreign table or Detail table. ✅ The table that defines the primary or unique key and is referenced by the foreign key is called the Primary table or Master table. 👉 Features 1)Master table cannot be updated if child records exists. 2)Records cannot be inserted or deleted into a detail table if corresponding records in the master table do not exist. 3)Records of the master table cannot be deleted if corresponding records in the detail table already exist. 👉 O...
Read more

Javascript-OOPs(Part3)-Inheritance - (9)

-
Image
   👉 Javascript with OOPs (Inheritance) In Javascript, Inheritance is done using prototype object. A prototype object is an object pointing to another object. We don't have a direct inheritance in Javascript, we can mimic inheritance using prototype. Let's say, we have one more class that inherits from Customer, and it submits to Server2. function CustomerChild(){         this.submit = function() {         alert ("this submits the data to Server2" + " "      +  this.CustomerName + " "                                       + this.CustomerCode");   }}             CustomerChild.prototype = new Customer(); var cust = new Customer(); cust.CustomerName ("John"); cust.Submit();  --this is a call to the submit method of the Customer class.  cust = new CustomerChild(); cust...
Read more

OraclePLSQL-Page3

-
Image
                                                                                          👉 Creating a table from a table Below SQL syntax populates the target table with data from the source table. To create a target table without the records from the source table, the SELECT statement must have a WHERE clause. The WHERE clause must specify a condition that cannot be specified. 👉 Inserting data into a table from another table It is used to populate a table with data that already exist in another table. 👉DELETE Command The DELETE command deletes the rows from the table that satisfies the condition and returns the number of records deleted.
Read more