PostgreSQL/Constraints/Constraints Basics

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Null column

   <source lang="sql">

postgres=# CREATE TABLE products ( postgres(# product_no integer NULL, postgres(# name text NULL, postgres(# price numeric NULL postgres(# ); CREATE TABLE postgres=# drop table products; DROP TABLE postgres=# postgres=#

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Specifying range check in table creation

   <source lang="sql">

postgres=# postgres=# postgres=# CREATE TABLE products ( postgres(# product_no integer, postgres(# name text, postgres(# price numeric CHECK (price > 0) postgres(# ); CREATE TABLE postgres=# postgres=# postgres=# drop table products; DROP TABLE postgres=#

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Specifying two constaint for a single table

   <source lang="sql">

postgres=# postgres=# postgres=# CREATE TABLE products ( postgres(# product_no integer NOT NULL, postgres(# name text NOT NULL, postgres(# price numeric NOT NULL CHECK (price > 0) postgres(# ); CREATE TABLE postgres=# postgres=# drop table products; DROP TABLE postgres=#

      </source>