![]() In this syntax, you specify the name of the UNIQUE constraint after the CONSTRAINT keyword. UNIQUE(column_list) Code language: SQL (Structured Query Language) ( sql ) To define a UNIQUE constraint with a name, you use this syntax: If you define a UNIQUE constraint without specifying a name, MySQL automatically generates a name for it. MySQL uses the combination of values in both column column_name1 and column_name2 to evaluate the uniqueness. In this syntax, you add a comma-separated list of columns in parentheses after the UNIQUE keyword. To define a UNIQUE constraint for two or more columns, you use the following syntax: CREATE TABLE table_name( And you can use it to enforce the unique rule for one column. This UNIQUE constraint is a column constraint. If you insert or update a value that causes duplicate in the column_name, MySQL rejects the change and issues an error. ![]() In this syntax, you include the UNIQUE keyword in the definition of the column that you want to enforce the uniqueness rule. ) Code language: SQL (Structured Query Language) ( sql ) To define a UNIQUE constraint for a column when you create a table, you use this syntax: CREATE TABLE table_name( A UNIQUE constraint can be either a column constraint or a table constraint. To enforce this rule, you use a UNIQUE constraint.Ī UNIQUE constraint is an integrity constraint that ensures values in a column or group of columns to be unique. For example, email addresses of users in the users table, or phone numbers of customers in the customers table should be unique. Sometimes, you want to ensure values in a column or a group of columns are unique. Summary: in this tutorial, you will learn about MySQL UNIQUE constraint and how to use UNIQUE constraint to enforce the uniqueness of values in a column or a group of columns in a table.
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