Types of SQL Keys

1. Different Type's of SQL Key's Primary key Super key Foreign key Alternate key Composite key Candidate key www.technogeekscs.com

2. What are Keys In SQL? In SQL, a key is a specific field or set of fields in a table that is used to uniquely identify each record in the table. www.technogeekscs.com

3. What is Primary Key? Primary key is column or group of columns to identify any row in a table. A primary key is a unique and non-null field or set of fields that can be used to identify a record in a table. Only one primary key can be defined for a table. Syntax:CREATE TABLE table_name ( column1 data_type PRIMARY KEY, column2 data_type, column3 data_type,..... ); www.technogeekscs.com

4. Uses of Primary Key It helps to improve performance of the database by creating unique index on it. It is used to update and delete records in the table. Primary keys help to enforce data integrity by ensuring that no duplicate records exist in a table. www.technogeekscs.com

5. What is Foreign Key? A Foreign key is a column which depends on primary key of another table. The table having foreign key is called as child table and the table having primary key is called parent table. Syntax:CREATE TABLE child_table ( column1 data_type, column2 data_type, column3 data_type, FOREIGN KEY (child_column) REFERENCES parent_table(parent_column), ... ); www.technogeekscs.com

6. Uses of Foreign key Providing flexibility in data modeling. Establishing relationships between tables in a database. A foreign key is used to establish a link between the data in two tables. It enables data modeling flexibility and support data normalization in foreign key. Foreign keys help to maintain data integrity by ensuring that the values in a foreign key field match the primary key of another table. www.technogeekscs.com

7. What is Super key? Super key is collection of one or more attributes to identify any row. When there is insufficient information to determine the primary key, a super key is created. Syntax: CREATE TABLE Employee ( EmployeeID INT PRIMARY KEY, FirstName VARCHAR(255), LastName VARCHAR(255), Salary DECIMAL(10,2), UNIQUE (FirstName, LastName) ); www.technogeekscs.com

8. Uses of Super key Creates clustered index on primary key for efficient data retrieval Allowing for efficient searching and sorting of data in the table. Establishes relationships between tables through foreign keys Improving query performance by using a super key as an index. Identifying a specific tuple in a table for update or deletion. www.technogeekscs.com

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