Types of Triggers in Oracle
What are the after triggers? Explanation: AFTER TRIGGERS can be classified further into three types as: AFTER INSERT Trigger, AFTER UPDATE Trigger, AFTER DELETE Trigger. Explanation: Example : declare @empid int; where empid is the variable.
Both DML and DDL triggers are nested when a trigger performs an action that initiates another trigger. These actions can initiate other triggers, and so on. DML and DDL triggers can be nested up to 32 levels.
How can we specifies a row-level trigger? Explanation: [FOR EACH ROW] − This specifies a row-level trigger, i.e., the trigger will be executed for each row being affected. Otherwise the trigger will execute just once when the SQL statement is executed, which is called a table level trigger.
Which SQL keyword is used to retrieve a maximum value? Explanation: The MAX() function returns the largest value of the selected column.
SELECT statements An SQL SELECT statement retrieves records from a database table according to clauses (for example, FROM and WHERE ) that specify criteria. The syntax is: SELECT column1, column2 FROM table1, table2 WHERE column2='value';
Which of the following is not a type of SQL statement? Explanation: Data Communication Language (DCL) is not a type of SQL statement. Explanation: The CREATE TABLE statement is used to create a table in a database. Tables are organized into rows and columns; and each table must have a name.
Feature ends with two 0's. Feature has more than two 0's. Feature has two 0's in it, at any position.
NULL in SQL: Indicating the Absence of Data. “Every [SQL] data type includes a special value, called the null value,”0 “that is used to indicate the absence of any data value”.
1) Make sure the column datatypes are the smallest necessary to comfortably fit the data. 2) Make sure you use date columns for dates, integer type columns for whole numbers that might have math done to them, VARCHAR when data width will vary, and NVARCHAR if you need to store more than one language.
0=0 is like TRUE. This is used when you want to dynamically append different conditions in the where clause of a select statement. In case there are no where clauses all records will be retured from the query. So in all 0=0 is not going to affect the results.
SQL is a query language, whereas MySQL is a relational database that uses SQL to query a database. You can use SQL to access, update, and manipulate the data stored in a database. ... SQL is used for writing queries for databases, MySQL facilitates data storing, modifying, and management in a tabular format.
Difference between WHERE and HAVING clause The WHERE clause is used in the selection of rows according to given conditions whereas the HAVING clause is used in column operations and is applied to aggregated rows or groups. If GROUP BY is used then it is executed after the WHERE clause is executed in the query.
A trigger is a special type of stored procedure that automatically runs when an event occurs in the database server. DML triggers run when a user tries to modify data through a data manipulation language (DML) event. ... SQL Server lets you create multiple triggers for any specific statement.
Procedure
You cant call Trigger from Stored Procedure, as Trigger are created on table and get fired implicitly. But you can call stored procedure to from trigger, but do remeber it should not be recursive.
A trigger defines a set of actions that are performed in response to an insert, update, or delete operation on a specified table. When such an SQL operation is executed, the trigger is said to have been activated. Triggers are optional and are defined using the CREATE TRIGGER statement.
Stored procedures are a pieces of the code in written in PL/SQL to do some specific task. On the other hand, trigger is a stored procedure that runs automatically when various events happen (eg update, insert, delete). ...
A cursor can be created within a trigger by writing the declare statement inside the trigger. A trigger cannot be created within a cursor. ... A cursor is activated and thus created in response to any SQL statement. A trigger is executed in response to a DDL statement, DML statement or any database operation.
Stored procedures in SQL are easier to create and functions have a more rigid structure and support less clauses and functionality. By the other hand, you can easily use the function results in T-SQL. We show how to concatenate a function with a string. Manipulating results from a stored procedure is more complex.
Views should be used to store commonly-used JOIN queries and specific columns to build virtual tables of an exact set of data we want to see. Stored procedures hold the more complex logic, such as INSERT, DELETE, and UPDATE statements to automate large SQL workflows.
No, a view is simply a stored text query. You can apply WHERE and ORDER against it, the execution plan will be calculated with those clauses taken into consideration.
Users cannot see or access the remaining data in the underlying tables. A view also serves as a mechanism to simplify query execution. Complex queries can be stored in the form as a view, and data from the view can be extracted using simple queries. A view consists of a SELECT statement that stored with a database.