Using MySQL Unique Constraints

A UNIQUE constraint is an integrity constraint that ensures values in a column or group of columns to be unique. A UNIQUE constraint can be either a column constraint or a table constraint. In this syntax, you include the UNIQUE keyword in the definition of the column that you want to enforce the uniqueness rule.

1. How do you use unique constraints?
2. How do I create a unique constraint in MySQL?
3. How do I find unique key constraints in MySQL?
4. Can I define multiple unique key in a MySQL table?
5. What is unique constraint violated?
6. What is unique constraint explain with example?
7. What are the constraints in MySQL?
8. How do you write a unique constraint in SQL?
9. Is primary key unique MySQL?
10. How do I find unique constraints in SQL?
11. What are SQL constraints?
12. What is unique key example?

How do you use unique constraints?

The UNIQUE constraint ensures that all values in a column are different. Both the UNIQUE and PRIMARY KEY constraints provide a guarantee for uniqueness for a column or set of columns. A PRIMARY KEY constraint automatically has a UNIQUE constraint.

How do I create a unique constraint in MySQL?

The syntax for creating a unique constraint using an ALTER TABLE statement in MySQL is: ALTER TABLE table_name ADD CONSTRAINT constraint_name UNIQUE (column1, column2, ... column_n);

How do I find unique key constraints in MySQL?

You can show unique constraints of a table in MySQL using information_schema. table_constraints.

Can I define multiple unique key in a MySQL table?

Unlike the PRIMARY KEY index, you can have more than one UNIQUE index per table. Another way to enforce the uniqueness of value in one or more columns is to use the UNIQUE constraint. When you create a UNIQUE constraint, MySQL creates a UNIQUE index behind the scenes.

What is unique constraint violated?

The ORA-00001 message is triggered when a unique constraint has been violated. Essentially the user causes the error when trying to execute an INSERT or UPDATE statement that has generated a duplicate value in a restricted field. ... The constraint name can be found by looking at the error message itself.

What is unique constraint explain with example?

SQL - UNIQUE Constraint. The UNIQUE Constraint prevents two records from having identical values in a column. In the CUSTOMERS table, for example, you might want to prevent two or more people from having an identical age.

What are the constraints in MySQL?

MySQL CONSTRAINT is used to define rules to allow or restrict what values can be stored in columns. The purpose of inducing constraints is to enforce the integrity of a database. MySQL CONSTRAINTS are used to limit the type of data that can be inserted into a table.

How do you write a unique constraint in SQL?

The syntax for creating a unique constraint using an ALTER TABLE statement in SQL Server is: ALTER TABLE table_name ADD CONSTRAINT constraint_name UNIQUE (column1, column2, ... column_n); table_name.

Is primary key unique MySQL?

3 Answers. Primary key is always unique in every SQL. You dont have to explicitly define it as UNIQUE. ... Also you can have only one primary key constraint in the table(as the point of creating a primary key is to uniquely identify the row in your table) but you can more than one unique key constraint in your table.

How do I find unique constraints in SQL?

Use sys. indexes, join the table, schema, object, and as an added bonus, you get not only unique constraints, but also unique indices, including filter.

What are 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 action, the action is aborted.

What is unique key example?

Example of Creating Unique Key

Consider the same student table with attributes, 1) StudID, 2) Roll No, 3) First Name, 4) Last Name, and 5) Email. Stud ID can have a unique constraint where entries in Stud ID column can be unique because each student of a university must have a unique ID number.