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>Chapter 37. The Rule System</H1
><DIV
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><DL
><DT
><B
>Table of Contents</B
></DT
><DT
>37.1. <A
HREF="querytree.html"
>The Query Tree</A
></DT
><DT
>37.2. <A
HREF="rules-views.html"
>Views and the Rule System</A
></DT
><DD
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>37.2.1. <A
HREF="rules-views.html#RULES-SELECT"
>How <TT
CLASS="COMMAND"
>SELECT</TT
> Rules Work</A
></DT
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>37.2.2. <A
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>View Rules in Non-<TT
CLASS="COMMAND"
>SELECT</TT
> Statements</A
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><DT
>37.2.3. <A
HREF="rules-views.html#AEN55562"
>The Power of Views in <SPAN
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>PostgreSQL</SPAN
></A
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>37.2.4. <A
HREF="rules-views.html#RULES-VIEWS-UPDATE"
>Updating a View</A
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>37.3. <A
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>Rules on <TT
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>INSERT</TT
>, <TT
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>UPDATE</TT
>, and <TT
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>DELETE</TT
></A
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>37.3.1. <A
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>How Update Rules Work</A
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>37.3.2. <A
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>Cooperation with Views</A
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>37.4. <A
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>Rules and Privileges</A
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><DT
>37.5. <A
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>Rules and Command Status</A
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>37.6. <A
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>Rules Versus Triggers</A
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><P
>     This chapter discusses the rule system in
     <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>.  Production rule systems
     are conceptually simple, but there are many subtle points
     involved in actually using them.</P
><P
>     Some other database systems define active database rules, which
     are usually stored procedures and triggers.  In
     <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>, these can be implemented
     using functions and triggers as well.</P
><P
>     The rule system (more precisely speaking, the query rewrite rule
     system) is totally different from stored procedures and triggers.
     It modifies queries to take rules into consideration, and then
     passes the modified query to the query planner for planning and
     execution.  It is very powerful, and can be used for many things
     such as query language procedures, views, and versions.  The
     theoretical foundations and the power of this rule system are
     also discussed in <A
HREF="biblio.html#STON90B"
><I
><A
HREF="http://db.cs.berkeley.edu/papers/ERL-M90-36.pdf"
TARGET="_top"
>    On Rules, Procedures, Caching and Views in Database Systems
    </A
></I
></A
> and <A
HREF="biblio.html#ONG90"
><I
>A Unified Framework for Version Modeling Using Production Rules in a Database System</I
></A
>.</P
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