![]() Now, try to execute the below SQL Statement. Duplicate entry ‘1’ for key ’employee.Id’ This is because we are trying to insert duplicate Id values into the Id column.Įrror Code: 1062. When we try to execute the above INSERT SQL statement, we will get the following error. INSERT INTO Employee (Id, Name, Email, Department) VALUES (1, ‘Sambit’, ‘IT’) When we execute the above INSERT statement, it executed as expected. INSERT INTO Employee (Id, Name, Email, Department) VALUES (1, ‘Anurag’, ‘IT’) Now try to execute the below SQL Insert statements. Once you execute the above SQL Statement, it will give you the below output.Īs we have applied the UNIQUE constraint to the Id and Email column, so here you can see the key column of these two fields have UNI value which indicates these two columns are the UNIQUE column. Once you execute the above query, let us verify the Employee table structure by executing the below SQL Statement. It means these two columns will not accept the duplicate value. As you can see, here, we applied the UNIQUE constraint to Id, and Email columns. ![]() In order to understand MySQL Unique Constraint, first, create the EmployeeDB and Employee table by executing the following SQL Script. Let us understand the Unique Constraint in MySQL with some examples. Example to understand MySQL UNIQUE Constraint: We can apply the UNIQUE constraint on any data type column such as INT, VARCHAR, etc. Multiple columns in a single table can have the UNIQUE Constraint. But it accepts NULL values in that column. That means the UNIQUE Constraint is useful to restrict storing of duplicate data row values in a given column or combination of columns. When you want a column or columns not to accept any duplicate values, then you need to apply UNIQUE Constraint for that column or columns in MySQL. Please read our previous article where we discussed NOT NULL Constraint in MySQL. In this article, I am going to discuss UNIQUE Constraint in MySQL with Examples. Data Structures and Algorithms Tutorialsīack to: MySQL Tutorials for Beginners and Professionals UNIQUE Constraint in MySQL with Examples.With this new knowledge at our fingertips, we can rewrite our previous CREATE TABLE statement by adding our two new constraints. While IDENTITY can accept two arguments of the numeric seed where the values will begin from as well as the increment, these values are typically not specified with the IDENTITY constraint and instead are left as defaults (both default to 1). The second piece of the puzzle is the IDENTITY constraint, which informs SQL Server to auto increment the numeric value within the specified column anytime a new record is INSERTED. ![]() In a multi-column scenario, individual columns can contain duplicate, non-unique values, but the PRIMARY KEY constraint ensures that every combination of constrained values will in fact be unique relative to every other combination. While SQL Server only allows one PRIMARY KEY constraint assigned to a single table, that PRIMARY KEY can be defined for more than one column. The first is PRIMARY KEY, which as the name suggests, forces the specified column to behave as a completely unique index for the table, allowing for rapid searching and queries. The solution turns out to be using two constraint options provided by SQL Server.
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