SQL PRIMARY KEY Constraint: SQL PRIMARY KEY is a Field in a table which uniquely identifies each record in a database table. Primary key ought to have ‘UNIQUE’ values. Primary key will never have ‘NULL’ values. Note: A table can only have one primary keys, which may contain one or multiple fields. Type of Keys: …
SQL FOREIGN KEY Constraint: SQL FOREIGN KEY is a key used to link two tables in a database. A foreign key one table refers to a primary key in other table Note 1: A table can only have one primary keys, which may contain one or multiple fields. Note 2: A table containing the foreign key …
SQL Constraints: SQL Constraints are the set of rules followed by SQL programming language. SQL is a procedural programming language.They are used to specify rules for the data. They put a condition , and limit to data entering the table. SQL Constraints could be divided into ‘2’ levels: Constraints could be of ‘Table level’ or …