Explore all SQL constraints with examples and real-world use cases. Learn PRIMARY KEY, FOREIGN KEY, UNIQUE, CHECK, and more.
There are several different types of constraints in SQL, including:NOT NULL PRIMARY KEY UNIQUE DEFAULT FOREIGN KEY CHECKNow, let's discuss each of these constraints in detail.NOT NULL ConstraintThe NOT NULL constraint specifies that the column does not accept NULL values....
Types of Constraints We will discuss the following constraints: Not Null Integrity Constraint By default all columns in a table can contain null values. If you want to ensure that a column must always have a value, i.e. it should not be left blank, then define a NOT NULL constraint on ...
Since we can specify constraints on a table, there needs to be a way to remove this constraint as well. In SQL, this is done via the ALTER TABLE statement. The SQL syntax to remove a constraint from a table is, ALTER TABLE "table_name" DROP [CONSTRAINT|INDEX] "CONSTRAINT_NAME";...
In this article, we explored the different types of integrity constraints in SQL and how to implement them using PostgreSQL. We covered primary keys, NOT NULL constraints, UNIQUE constraints, DEFAULT constraints, CHECK constraints, and FOREIGN KEY constraints, providing practical examples for each. By...
data table, i.e., constraints are basically limitations or restrictions on the data type. Hence, they ensure the data’s reliability, consistency, and accuracy. In SQL, we will come across the following types of constraints. Here is an overview of the generic purpose that these constraints ...
SQL NOT NULL UNIQUE PRIMARY KEY FOREIGN KEY CHECK DEFAULT In this article, we will go through the first three constraints; SQL NOT NULL, UNIQUE and SQL PRIMARY KEY, and we will complete the rest three constraints in the next article. Let us start discussing each one of these SQL...
Let’s visit some commonly used constraints so you can get an idea as to what exactly can be accomplished with these types of commands. DEFAULT Constraint This constraint proves a default value for a column when you don’t have one specified. If you are trying to insert system values, you...
Types of Oracle Constraints Oracle has multiple types of constraints for multiple purposes. In this section, we are going to go through the different types of constraints in Oracle. 1. NOT NULL If we just add a column, by default the column is allowed to hold NULL values but in case ther...
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