In this hindi free course SQL constraints are used to define the rules for data in a database.
We use them to ensure data integrity and consistency, limit the consequences of user errors, and enforce business rules.
There are three types of SQL constraints: column-level constraints, table-level constraints, and domain-range constraints.
Column-level constraints typically refer to individual columns in a table or view. They can be used to specify that certain values are not allowed for that column or that all values in the column must be unique. This is done through specifying NULL values, UNIQUE indexes, PRIMARY KEYs (or UNIQUE), CHECKs (or NOT NULL), or FOREIGN KEYs as appropriate.