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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.
With the distinct keyword with single and multiple column names, you get distinct records: SELECT DISTINCT column 1, column 2, ... FROM table_name;
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.
23 sty 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 lut 2021 · When to Use a Unique Constraint (with Examples) Example 1: Unique Values. We use a UNIQUE constraint when the column must contain a unique value for each row. Let’s consider the Person table. Each person has a name, age, and a date of birth.
In this tutorial, you will learn how to enforce the uniqueness of values in a column or a set of columns using the SQL UNIQUE constraint.
20 gru 2023 · You can create a unique constraint in SQL Server by using SQL Server Management Studio or Transact-SQL to ensure no duplicate values are entered in specific columns that don't participate in a primary key. Creating a unique constraint automatically creates a corresponding unique index. Note.
