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mirror of https://github.com/postgres/postgres.git synced 2025-12-21 05:21:08 +03:00

A bit of minor copy-editing.

This commit is contained in:
Tom Lane
2005-10-23 19:29:49 +00:00
parent 55337e40b3
commit 7d3ab8ac55
2 changed files with 18 additions and 8 deletions

View File

@@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/ddl.sgml,v 1.44 2005/08/13 01:55:41 momjian Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/ddl.sgml,v 1.45 2005/10/23 19:29:49 tgl Exp $ -->
<chapter id="ddl">
<title>Data Definition</title>
@@ -240,7 +240,7 @@ CREATE TABLE products (
in a table. For many applications, however, the constraint they
provide is too coarse. For example, a column containing a product
price should probably only accept positive values. But there is no
data type that accepts only positive numbers. Another issue is
standard data type that accepts only positive numbers. Another issue is
that you might want to constrain column data with respect to other
columns or rows. For example, in a table containing product
information, there should only be one row for each product number.
@@ -431,7 +431,7 @@ CREATE TABLE products (
IS NOT NULL)</literal>, but in
<productname>PostgreSQL</productname> creating an explicit
not-null constraint is more efficient. The drawback is that you
cannot give explicit names to not-null constraints created that
cannot give explicit names to not-null constraints created this
way.
</para>
@@ -551,7 +551,7 @@ CREATE TABLE products (
columns included in the constraint are equal.
However, null values are not considered equal in this
comparison. That means even in the presence of a
unique constraint it is possible to store an unlimited number of
unique constraint it is possible to store duplicate
rows that contain a null value in at least one of the constrained
columns. This behavior conforms to the SQL standard, but we have
heard that other SQL databases may not follow this rule. So be