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Luckily, MySQL provides another kind of index called UNIQUE index that allows you to enforce the uniqueness of values in one or more columns. Unlike the PRIMARY KEY index, you can have more than one UNIQUE index per table. To create a UNIQUE index, you use the CREATE UNIQUE INDEX statement as follows:
- Indexes
Unique indexes – use unique indexes to ensure distinct...
- Indexes
CREATE UNIQUE INDEX Syntax. Creates a unique index on a table. Duplicate values are not allowed: CREATE UNIQUE INDEX index_name. ON table_name (column1, column2, ...); MySQL CREATE INDEX Example. The SQL statement below creates an index named "idx_lastname" on the "LastName" column in the "Persons" table: CREATE INDEX idx_lastname.
CREATE INDEX enables you to add indexes to existing tables. CREATE INDEX is mapped to an ALTER TABLE statement to create indexes. See Section 15.1.9, “ALTER TABLE Statement”. CREATE INDEX cannot be used to create a PRIMARY KEY; use ALTER TABLE instead.
5 sty 2024 · The syntax for creating a UNIQUE INDEX involves the CREATE INDEX statement. Creating a UNIQUE INDEX on a Single Column: CREATE UNIQUE INDEX index_unique_column ON tbl_name (col_name); Creating a UNIQUE INDEX on Multiple Columns: CREATE UNIQUE INDEX index_unique_columns ON tbl_name (co1, col2, …);
Unique indexes – use unique indexes to ensure distinct values stored in a column. Prefix indexes – show you how to use the prefix index to create an index for a character string column. Invisible indexes – cover the index visibility and show you how to make an index visible or invisible.
Learn how to create and use unique indexes in MySQL to prevent duplicate values in specified columns and speed up data retrieval. See syntax, examples, and tips for designing tables with unique indexes.
A unique index can be created on one or more columns of a table using the CREATE UNIQUE INDEX statement in MySQL. If we are creating unique index on only a single column, all the rows in that column must be unique.
