Yahoo India Web Search

Search results

1. www.w3schools.com › sqL › sql_uniqueSQL UNIQUE Constraint - W3Schools

   www.w3schools.com › sqL › sql_unique

   • Cached

   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.

2. learnsql.com › blog › unique-constraint-in-sqlWhat Is a Unique Constraint in SQL? - LearnSQL.com

   learnsql.com › blog › unique-constraint-in-sql

   • Cached

   Feb 4, 2021 · A constraint is a rule that makes a column fulfill a particular condition (i.e. it prevents the user from entering the wrong type of data). A UNIQUE constraint dictates that a column must not store duplicate values. Let’s see an example using the Employees table.

3. www.geeksforgeeks.org › sql-unique-constraintSQL | UNIQUE Constraint - GeeksforGeeks

   www.geeksforgeeks.org › sql-unique-constraint

   • Cached

   Jan 23, 2024 · SQL Constraints Unique constraints in SQL is used to check whether the sub-query has duplicate tuples in its result. It returns a boolean value indicating the presence/absence of duplicate tuples. Unique constraint returns true only if the subquery has no duplicate tuples, else it returns false.

4. www.programiz.com › sql › uniqueSQL UNIQUE Constraint (With Examples) - Programiz

   www.programiz.com › sql › unique

   • Cached

   In SQL, the UNIQUE constraint in a column means that the column must have a unique value. In this tutorial, you will learn about the SQL UNIQUE constraint with the help of examples.

5. www.sqltutorial.org › sql-unique-constraintSQL UNIQUE Constraint: Enforce Uniqueness of Values

   www.sqltutorial.org › sql-unique-constraint

   • Cached

   By definition, an SQL UNIQUE constraint defines a rule that prevents duplicate values stored in specific columns that do not participate a primary key. UNIQUE vs. PRIMARY KEY constraints. You can have at most one PRIMARY KEY constraint whereas you can have multiple UNIQUE constraints in a table.

6. learn.microsoft.com › en-us › sqlUnique constraints and check constraints - SQL Server

   learn.microsoft.com › en-us › sql

   • Cached

   Jan 2, 2024 · Constraints are rules that the SQL Server Database Engine enforces for you. For example, you can use UNIQUE constraints to make sure that no duplicate values are entered in specific columns that don't participate in a primary key.

7. People also ask

   What is a unique constraint in SQL?

   • The UNIQUE constraint is one of many SQL constraints that can be defined for a column. A constraint is a rule that makes a column fulfill a particular condition (i.e. it prevents the user from entering the wrong type of data). A UNIQUE constraint dictates that a column must not store duplicate values. Let’s see an example using the Employees table.

   What Is a Unique Constraint in SQL? - LearnSQL.com

   learnsql.com/blog/unique-constraint-in-sql/

   See all results for this question

   How do I create a unique constraint?

   • MySQL / SQL Server / Oracle / MS Access: To create a UNIQUE constraint on the "ID" column when the table is already created, use the following SQL: MySQL / SQL Server / Oracle / MS Access: To name a UNIQUE constraint, and to define a UNIQUE constraint on multiple columns, use the following SQL syntax: MySQL / SQL Server / Oracle / MS Access:

   SQL UNIQUE Constraint - W3Schools

   www.w3schools.com/sqL/sql_unique.asp

   See all results for this question

   What happens if a unique constraint is added to a column?

   • When a UNIQUE constraint is added to an existing column or columns in the table, by default, the Database Engine examines the existing data in the columns to make sure all values are unique. If a UNIQUE constraint is added to a column that has duplicate values, the Database Engine returns an error and doesn't add the constraint.

   Unique constraints and check constraints - SQL Server

   learn.microsoft.com/en-us/sql/relational-databases/tables/unique-constraints-and-check-constraints?view=sql-server-ver16

   See all results for this question

   How to define a unique constraint for a group of columns?

   • To define a UNIQUE constraint for a group of columns, you write it as a table constraint with column names separated by commas as follows: key_column data_type PRIMARY KEY , column1 data_type, column2 data_type, column3 data_type, ..., UNIQUE (column1,column2) Code language: SQL (Structured Query Language) (sql)

   An Essential Guide to SQL Server UNIQUE Constraint

   www.sqlservertutorial.net/sql-server-basics/sql-server-unique-constraint/

   See all results for this question

8. www.sqlservertutorial.net › sql-server-basics › sqlAn Essential Guide to SQL Server UNIQUE Constraint

   www.sqlservertutorial.net › sql-server-basics › sql

   • Cached

   SQL Server UNIQUE constraints allow you to ensure that the data stored in a column, or a group of columns, is unique among the rows in a table. The following statement creates a table whose data in the email column is unique among the rows in the hr.persons table: CREATE SCHEMA hr; GO.