PostgreSQL/Constraints/Unique — различия между версиями
Admin (обсуждение | вклад) м (1 версия) |
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(нет различий)
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Версия 16:45, 26 мая 2010
Содержание
Assign your own name for a unique constraint
<source lang="sql">
postgres=# -- Assign your own name for a unique constraint postgres=# postgres=# CREATE TABLE products ( postgres(# product_no integer CONSTRAINT must_be_different UNIQUE, postgres(# name text, postgres(# price numeric postgres(# ); NOTICE: CREATE TABLE / UNIQUE will create implicit index "must_be_different" for table "products" CREATE TABLE postgres=# postgres=# postgres=# drop table products; DROP TABLE postgres=# postgres=#
</source>
Specifying the unique column using Unique function
<source lang="sql">
postgres=# postgres=# CREATE TABLE products ( postgres(# product_no integer, postgres(# name text, postgres(# price numeric, postgres(# UNIQUE (product_no) postgres(# ); NOTICE: CREATE TABLE / UNIQUE will create implicit index "products_product_no_key" for table "products" CREATE TABLE postgres=# postgres=# drop table products; DROP TABLE postgres=# postgres=# postgres=#
</source>
Unique and not null column
<source lang="sql">
postgres=# postgres=# CREATE TABLE products ( postgres(# product_no integer UNIQUE NOT NULL, postgres(# name text, postgres(# price numeric postgres(# ); NOTICE: CREATE TABLE / UNIQUE will create implicit index "products_product_no_key" for table "products" CREATE TABLE postgres=# postgres=# drop table products; DROP TABLE postgres=# postgres=#
</source>
Unique constraint refers to a group of columns, the columns are listed separated by commas
<source lang="sql">
postgres=# postgres=# postgres=# -- Unique constraint refers to a group of columns, the columns are listed separated by commas: postgres=# postgres=# CREATE TABLE example ( postgres(# a integer, postgres(# b integer, postgres(# c integer, postgres(# UNIQUE (a, c) postgres(# ); NOTICE: CREATE TABLE / UNIQUE will create implicit index "example_a_key" for table "example" CREATE TABLE postgres=# postgres=# drop table example; DROP TABLE postgres=#
</source>
Unique Constraints
<source lang="sql">
postgres=# postgres=# -- Unique Constraints postgres=# postgres=# CREATE TABLE products ( postgres(# product_no integer UNIQUE, postgres(# name text, postgres(# price numeric postgres(# ); NOTICE: CREATE TABLE / UNIQUE will create implicit index "products_product_no_key" for table "products" CREATE TABLE postgres=# postgres=# drop table products; DROP TABLE postgres=# postgres=#
</source>