Types of Constraints in SQL There are different types of SQL constraints to aim for the accuracy and consistency of data in a table. Here are some common types of constraints, where we will clarify your understanding of SQL constraint syntax and examples: 1.NOT NULLConstraint The NOT NULL con...
-- create a table with unique constraint on college_code columnCREATETABLEColleges ( college_codeVARCHAR(20)UNIQUE, college_nameVARCHAR(50) ); Here, the values of thecollege_codecolumn must be unique. SQL UNIQUE Constraint Syntax The syntax of the SQLUNIQUEconstraint is: CREATETABLEtable_name (...
Create Named CHECK Constraint It's a good practice to createnamed constraintsso that it is easier to alter and drop constraints. Here's an example to create a namedCHECKconstraint: -- create a named constraint named amountCK-- the constraint makes sure that amount is greater than 0CREATETABLE...
SQL Constraints SQL constraints are used to specify rules for the data in a table. Constraints are used to limit the type of data that can go into a table. This ensures the accuracy and reliability of the data in the table. If there is any violation between the constraint and the data ...
SQL | Constraints: In this tutorial, we are going to learn about the various constraints in SQL with its usages, syntaxes and query examples.
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Integrity constraints in SQL are rules enforced on database tables to maintain data accuracy, consistency, and validity, such as ensuring unique primary keys and valid foreign key relationships.
Assertions CREATE ASSERTION <name> CHECK ( <condition> ); These are database-schema elements, like relations or views An assertion is a statement in SQL that ensures a certain condition will always exist in the database. Assertions are like column and table constraints, except that they are ...
SQL QUERY EXAMPLES Other related articles: Recently viewed articles: SQL Introduction Structured Query Language, most often called (S-Q-L), is Database Query Language used to manipulate and extract data from Database. It was originally called Structured English Query Language (in short SEQUEL) by...
Managing SQL constraints ADD CONSTRAINT Add a key, check, or unique constraint to a column. ALTER TABLE users ADD CONSTRAINT id_name_unique UNIQUE (id, name); DROP CONSTRAINT Remove a constraint from a column. ALTER TABLE users DROP CONSTRAINT id_name_unique; ...