Thread by @souravWD

⬒ Types of keys in SQL

A Thread 🧵

🔹What is key in SQL ?
⇥ A key in SQL is an attribute or a set of attribute which helps us to uniquely identify a record or a row of data in a relation table.

🔹 Primary key 🗝️
⇥ A primary key is a table attribute or column that identify every record present in a table uniquely.

There can be only one primary key attribute in a table and primary key column elements can't be some or null values.

🔹 Super Key
⇥ it is the set of all columns which help to identify Rows in a table uniquely.

🔹 Condidate Key
⇥ A Condidate Key is a column or a set of column that can qualify as a primary key in the database. There can be multiple candidate key in a table and only one Condidate Key can qualify as the primary key.

🔹 Composite Key
⇥ it is a set of tow or more attribute that helps to identify each tuple uniquely.

Any key such as super, primary, or candidate key etc... Can be called Composite key if it has more than on attributes.

🔹Foreign Key
⇥ A Foreign key is a key used to link tow table together. This is something also called as a referencing key.

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