Gbase8s unique index and non unique index

Unique indexes are not allowed to have duplicate values in columns , It can be used to define and constrain the combined values of one or more columns in the table , In execution insert and update Statement needs to be checked for uniqueness .GBase8s Middle primary key （PRIMARY KEY） Will automatically create a unique index . A good table design should define a primary key or a unique constraint index . Especially in OLTP In the system , A unique index can help quickly locate a small number of records .

Syntax for creating unique indexes ：

CREATE UNIQUE INDEX idx_name ON tabname(col);

perhaps

CREATE DISTINCT INDEX idx_name ON tabname(col);

Non unique index （ Repeatable index ） You can create , Allow duplicate data in columns . However, it is necessary to avoid creating indexes on data columns with duplicate subkeys , Because the index with more duplicate values , The lower its efficiency .

The example diagram of unique index and non unique index is as follows ：

Be careful ： Because of the need in insert、update Make uniqueness judgment when , Therefore, it is not recommended to create multiple unique indexes on a table . To ensure uniqueness requirements , Generally, it is enough to create a unique index in a table .