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