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SQL UNIQUE Constraint. 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.
With the distinct keyword with single and multiple column names, you get distinct records: SELECT DISTINCT column 1, column 2, ... FROM table_name;
Feb 4, 2021 · The UNIQUE constraint is used to enforce the uniqueness of values in a column or in a set of columns in a particular table – that is, for columns that are not included in the table’s primary key set. The difference between PRIMARY KEY and UNIQUE is that UNIQUE allows NULL values, while PRIMARY KEY does not.
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.
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.
SQL unique constraint is a type of constraint that ensures that the data in a column or set of columns is unique across all rows in a table. It is used to prevent duplicate values from being inserted into a table and to ensure data integrity.
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.
Mar 3, 2024 · The UNIQUE constraint is crucial for preventing duplicate entries in your database columns, which is key to maintaining clean and reliable data. Whether you’re a budding developer or a seasoned data architect, understanding how to implement this constraint can significantly impact your database’s performance and accuracy.
SQL Server UNIQUE Constraint. Summary: in this tutorial, you will learn how to use the SQL Server UNIQUE constraint to ensure the uniqueness of data contained in a column or a group of columns.
May 20, 2021 · The UNIQUE keyword in SQL plays the role of a database constraint; it ensures there are no duplicate values stored in a particular column or a set of columns. On the other hand, the DISTINCT keyword is used in the SELECT statement to fetch distinct rows from a table. The best place to learn about SQL and databases is LearnSQL.com.
