The query is then identified as a<I>Utility</I> query or a more complex

query. A<I>Utility</I> query is processed by a query-specific function

in<AHREF="../../backend/commands"> commands.</A> A complex query, like

<CODE>SELECT, UPDATE,</CODE> and

<CODE>DELETE</CODE> requires much more handling.

<I>SELECT, UPDATE,</I> and

<I>DELETE</I> requires much more handling.

The parser takes a complex query, and creates a

<AHREF="../../include/nodes/parsenodes.h">Query</A> structure that

contains all the elements used by complex queries. Query.qual holds the

<CODE>WHERE</CODE> clause qualification, which is filled in by

<I>WHERE</I> clause qualification, which is filled in by

<AHREF="../../backend/parser/parse_clause.c">transformWhereClause().</A>

Each table referenced in the query is represented by a<A

HREF="../../include/nodes/parsenodes.h"> RangeTableEntry,</A> and they

are linked together to form the<I>range table</I> of the query, which is

generated by<AHREF="../../backend/parser/parse_clause.c">

makeRangeTable().</A> Query.rtable holds the query's range table.

Certain queries, like<CODE>SELECT,</CODE> return columns of data. Other

queries, like<CODE>INSERT</CODE> and<CODE>UPDATE,</CODE> specify the columns

Certain queries, like<I>SELECT,</I> return columns of data. Other

queries, like<I>INSERT</I> and<I>UPDATE,</I> specify the columns

modified by the query. These column references are converted to<A

HREF="../../include/nodes/primnodes.h">Resdom</A> entries, which are

linked together to make up the<I>target list</I> of the query. The

target list is stored in Query.targetList, which is generated by

<AHREF="../../backend/parser/parse_target.c">transformTargetList().</A>

Other query elements, like aggregates(<CODE>SUM()</CODE>),<CODE>GROUP BY,</CODE>

and<CODE>ORDER BY</CODE> are also stored in their own Query fields.

Other query elements, like aggregates(<I>SUM()</I>),<I>GROUP BY,</I>

and<I>ORDER BY</I> are also stored in their own Query fields.

The next step is for the Query to be modified by any<CODE>VIEWS</CODE> or

<CODE>RULES</CODE> that may apply to the query. This is performed by the<A

The next step is for the Query to be modified by any<I>VIEWS</I> or

<I>RULES</I> that may apply to the query. This is performed by the<A

HREF="../../backend/rewrite">rewrite</A> system.

The<AHREF="../../backend/optimizer">optimizer</A> takes the Query

operations to be performed to execute the query. The<A

HREF="../../backend/optimizer/path">path</A> module determines the best

table join order and join type of each table in the RangeTable, using

Query.qual(<CODE>WHERE</CODE> clause) to consider optimal index usage.

Query.qual(<I>WHERE</I> clause) to consider optimal index usage.

The Plan is then passed to the<A

HREF="../../backend/executor">executor</A> for execution, and the result