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PostgreSQL/Constraints/Unique - История изменений
2026-04-07T04:43:33Z
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http://sqle.ru/index.php?title=PostgreSQL/Constraints/Unique&diff=4958&oldid=prev
в 13:45, 26 мая 2010
2010-05-26T13:45:56Z
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http://sqle.ru/index.php?title=PostgreSQL/Constraints/Unique&diff=4959&oldid=prev
Admin: 1 версия
2010-05-26T10:14:31Z
<p>1 версия</p>
<p><b>Новая страница</b></p><div>==Assign your own name for a unique constraint==<br />
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<!-- start source code --><br />
<br />
<source lang="sql"><br />
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postgres=# -- Assign your own name for a unique constraint<br />
postgres=#<br />
postgres=# CREATE TABLE products (<br />
postgres(# product_no integer CONSTRAINT must_be_different UNIQUE,<br />
postgres(# name text,<br />
postgres(# price numeric<br />
postgres(# );<br />
NOTICE: CREATE TABLE / UNIQUE will create implicit index "must_be_different" for table "products"<br />
CREATE TABLE<br />
postgres=#<br />
postgres=#<br />
postgres=# drop table products;<br />
DROP TABLE<br />
postgres=#<br />
postgres=#<br />
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</source><br />
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==Specifying the unique column using Unique function==<br />
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<!-- start source code --><br />
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<source lang="sql"><br />
postgres=#<br />
postgres=# CREATE TABLE products (<br />
postgres(# product_no integer,<br />
postgres(# name text,<br />
postgres(# price numeric,<br />
postgres(# UNIQUE (product_no)<br />
postgres(# );<br />
NOTICE: CREATE TABLE / UNIQUE will create implicit index "products_product_no_key" for table "products"<br />
CREATE TABLE<br />
postgres=#<br />
postgres=# drop table products;<br />
DROP TABLE<br />
postgres=#<br />
postgres=#<br />
postgres=#<br />
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</source><br />
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==Unique and not null column==<br />
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<!-- start source code --><br />
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<source lang="sql"><br />
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postgres=#<br />
postgres=# CREATE TABLE products (<br />
postgres(# product_no integer UNIQUE NOT NULL,<br />
postgres(# name text,<br />
postgres(# price numeric<br />
postgres(# );<br />
NOTICE: CREATE TABLE / UNIQUE will create implicit index "products_product_no_key" for table "products"<br />
CREATE TABLE<br />
postgres=#<br />
postgres=# drop table products;<br />
DROP TABLE<br />
postgres=#<br />
postgres=#<br />
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</source><br />
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==Unique constraint refers to a group of columns, the columns are listed separated by commas==<br />
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<!-- start source code --><br />
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<source lang="sql"><br />
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postgres=#<br />
postgres=#<br />
postgres=# -- Unique constraint refers to a group of columns, the columns are listed separated by commas:<br />
postgres=#<br />
postgres=# CREATE TABLE example (<br />
postgres(# a integer,<br />
postgres(# b integer,<br />
postgres(# c integer,<br />
postgres(# UNIQUE (a, c)<br />
postgres(# );<br />
NOTICE: CREATE TABLE / UNIQUE will create implicit index "example_a_key" for table "example"<br />
CREATE TABLE<br />
postgres=#<br />
postgres=# drop table example;<br />
DROP TABLE<br />
postgres=#<br />
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</source><br />
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==Unique Constraints==<br />
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<!-- start source code --><br />
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<source lang="sql"><br />
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postgres=#<br />
postgres=# -- Unique Constraints<br />
postgres=#<br />
postgres=# CREATE TABLE products (<br />
postgres(# product_no integer UNIQUE,<br />
postgres(# name text,<br />
postgres(# price numeric<br />
postgres(# );<br />
NOTICE: CREATE TABLE / UNIQUE will create implicit index "products_product_no_key" for table "products"<br />
CREATE TABLE<br />
postgres=#<br />
postgres=# drop table products;<br />
DROP TABLE<br />
postgres=#<br />
postgres=#<br />
<br />
</source></div>
Admin