SQL Tutorial

SQL - Foreign Key Constraint
In SQL, a Foreign Key is a column in one table that refers to the Primary Key in another table, creating a connection between the two tables.
SQL - JOINS
The JOIN clause in SQL is used to combine rows from two or more tables based on a related column between them. It allows you to retrieve data from multiple tables as if they were a single table.
SQL BACKUP DATABASE
The SQL BACKUP DATABASE statement is used to create a backup copy of an existing database. A backup is a safety copy of your database that you can restore later in case something goes wrong, such as accidental deletion, data corruption, or server failure.
SQL - NULL Values
SQL uses the term NULL to represent a non-existent data value in the database. These values are not the same as an empty string or a zero. They don't hold any space in the database and are used to signify the absence of a value or the unknown value in a data field.
Left Join vs Right Join
Both LEFT JOIN and RIGHT JOIN are types of outer joins in SQL. They are used to combine rows from two tables based on a related column, but they differ in which table's rows are preserved when there is no match.
SQL - Self Join
A SELF JOIN is a type of join in SQL where a table is joined with itself. This is used when you need to compare rows within the same table or find relationships among data stored in a single table. You can use aliases to distinguish between the two instances of the same table.

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