Journey of DLithe Bootcamp .NET Full Stack Developer | Week 6(Feb28-Mar5)
Structured Query Language (SQL)
SQL JOIN
A JOIN clause is used to combine rows from two or more tables, based on a related column between them.
Different Types of SQL JOINs
Here are the different types of the JOINs in SQL:
(INNER) JOIN: Returns records that have matching values in both tables
LEFT (OUTER) JOIN: Returns all records from the left table, and the matched records from the right table
RIGHT (OUTER) JOIN: Returns all records from the right table, and the matched records from the left table
FULL (OUTER) JOIN: Returns all records when there is a match in either left or right table
SQL INNER JOIN Keyword
The INNER JOIN keyword selects records that have matching values in both tables.
SQL LEFT JOIN Keyword
The LEFT JOIN keyword returns all records from the left table (table1), and the matching records from the right table (table2). The result is 0 records from the right side, if there is no match.
SQL RIGHT JOIN Keyword
The RIGHT JOIN keyword returns all records from the right table (table2), and the matching records from the left table (table1). The result is 0 records from the left side, if there is no match.
SQL FULL OUTER JOIN Keyword
The FULL OUTER JOIN keyword returns all records when there is a match in left (table1) or right (table2) table records.
Tip: FULL OUTER JOIN and FULL JOIN are the same.
SQL Self Join
A self join is a regular join, but the table is joined with itself.
Date: 02–03–2022
Triggers in SQL
A trigger in SQL is a procedural code that is automatically executed in response to certain events on a specified table. It is important to understand how these small codes make such a huge difference in database performance.
What is a Trigger?
Triggers are the SQL codes that are automatically executed in response to certain events on a particular table. These are used to maintain the integrity of the data. A trigger in SQL works similar to a real-world trigger.
Types of Triggers
There are two types of triggers:
- DDL Trigger
- DML Trigger
DDL Triggers
The DDL triggers are fired in response to DDL (Data Definition Language) command events that start with Create, Alter and Drop, such as Create_table, Create_view, drop_table, Drop_view and Alter_table.
DML Triggers
The DML triggers are fired in response to DML (Data Manipulation Language) command events that start with Insert, Update, and Delete. Like insert_table, Update_view and Delete_table.
AFTER Triggers
AFTER triggers are executed after the action of an INSERT, UPDATE, or DELETE statement.
