Αποτελέσματα Αναζήτησης
CREATE UNIQUE INDEX. The CREATE UNIQUE INDEX command creates a unique index on a table (no duplicate values allowed) Indexes are used to retrieve data from the database very fast. The users cannot see the indexes, they are just used to speed up searches/queries.
- CREATE VIEW
W3Schools offers free online tutorials, references and...
- CREATE VIEW
What is a unique index? A unique index on a column is an index on that column that also enforces the constraint that you cannot have two equal values in that column in two different rows. Example: CREATE TABLE table1 (foo int, bar int); CREATE UNIQUE INDEX ux_table1_foo ON table1(foo); -- Create unique index on foo.
5 Μαΐ 2023 · This topic describes how to create a unique index on a table in SQL Server by using SQL Server Management Studio or Transact-SQL. A unique index guarantees that the index key contains no duplicate values and therefore every row in the table is in some way unique.
5 Ιαν 2024 · In MySQL, a unique index is a crucial tool for ensuring that values in a specific column or a group of columns within a table are unique. This feature is essential to maintain data integrity by preventing duplicate entries where uniqueness is required.
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.
A unique index ensures the index key columns do not contain any duplicate values. A unique index may consist of one or many columns. If a unique index has one column, the values in this column will be unique.
26 Σεπ 2024 · PostgreSQL automatically creates a unique index when a unique constraint or primary key is defined for a table. The index covers the columns that make up the primary key or unique constraint (a multicolumn index, if appropriate), and is the mechanism that enforces the constraint.
