What is SQL Constraints?

Question

SQL Constraints

SQL constraints are used to specify rules for table data.

The following are commonly used SQL constraints:
NOT NULL - Indicates that a column cannot contain any NULL value.
UNIQUE - Does not allow to insert a duplicate value in a column. The UNIQUE constraint maintains the uniqueness of a column in a table. More than one UNIQUE column can be used in a table.
PRIMARY KEY - Enforces the table to accept unique data for a specific column and this constraint create a unique index for acc

Answer 1

In this context, it means requirement.