diff options
Diffstat (limited to 'doc/src/sgml/ref')
| -rw-r--r-- | doc/src/sgml/ref/create_operator.sgml | 93 |
1 files changed, 49 insertions, 44 deletions
diff --git a/doc/src/sgml/ref/create_operator.sgml b/doc/src/sgml/ref/create_operator.sgml index 02961e38a1c..eda81ffa895 100644 --- a/doc/src/sgml/ref/create_operator.sgml +++ b/doc/src/sgml/ref/create_operator.sgml @@ -15,7 +15,7 @@ </refnamediv> <REFSYNOPSISDIV> <REFSYNOPSISDIVINFO> - <DATE>1998-09-09</DATE> + <DATE>1999-04-14</DATE> </REFSYNOPSISDIVINFO> <SYNOPSIS> CREATE OPERATOR <replaceable>name</replaceable> ( @@ -25,15 +25,16 @@ CREATE OPERATOR <replaceable>name</replaceable> ( [, COMMUTATOR = <replaceable class="parameter">com_op</replaceable> ] [, NEGATOR = <replaceable class="parameter">neg_op</replaceable> ] [, RESTRICT = <replaceable class="parameter">res_proc</replaceable> ] - [, HASHES ] [, JOIN = <replaceable class="parameter">join_proc</replaceable> ] - [, SORT = <replaceable class="parameter">sort_op</replaceable> [, ...] ] + [, HASHES ] + [, SORT1 = <replaceable class="parameter">left_sort_op</replaceable> ] + [, SORT2 = <replaceable class="parameter">right_sort_op</replaceable> ] ) </SYNOPSIS> <REFSECT2 ID="R2-SQL-CREATEOPERATOR-1"> <REFSECT2INFO> - <DATE>1998-09-09</DATE> + <DATE>1999-04-14</DATE> </REFSECT2INFO> <TITLE> Inputs @@ -89,7 +90,7 @@ omitted for a left-unary operator. </TERM> <LISTITEM> <PARA> -The corresponding commutative operator. +The commutator for this operator. </PARA> </LISTITEM> </VARLISTENTRY> @@ -99,7 +100,7 @@ The corresponding commutative operator. </TERM> <LISTITEM> <PARA> -The corresponding negation operator. +The negator of this operator. </PARA> </LISTITEM> </VARLISTENTRY> @@ -109,7 +110,17 @@ The corresponding negation operator. </TERM> <LISTITEM> <PARA> -The corresponding restriction operator. +The restriction selectivity estimator function for this operator. + </PARA> + </LISTITEM> + </VARLISTENTRY> + <VARLISTENTRY> + <TERM> + <replaceable class="parameter">join_proc</replaceable> + </TERM> + <LISTITEM> + <PARA> +The join selectivity estimator function for this operator. </PARA> </LISTITEM> </VARLISTENTRY> @@ -119,27 +130,27 @@ HASHES </TERM> <LISTITEM> <PARA> -This operator can support a hash-join algorithm. +Indicates this operator can support a hash-join algorithm. </PARA> </LISTITEM> </VARLISTENTRY> <VARLISTENTRY> <TERM> - <replaceable class="parameter">join_proc</replaceable> + <replaceable class="parameter">left_sort_op</replaceable> </TERM> <LISTITEM> <PARA> -Procedure supporting table joins. +Operator that sorts the left-hand data type of this operator. </PARA> </LISTITEM> </VARLISTENTRY> <VARLISTENTRY> <TERM> - <replaceable class="parameter">sort_op</replaceable> + <replaceable class="parameter">right_sort_op</replaceable> </TERM> <LISTITEM> <PARA> -Operator to use for sorting. +Operator that sorts the right-hand data type of this operator. </PARA> </LISTITEM> </VARLISTENTRY> @@ -149,7 +160,7 @@ Operator to use for sorting. <REFSECT2 ID="R2-SQL-CREATEOPERATOR-2"> <REFSECT2INFO> - <DATE>1998-09-09</DATE> + <DATE>1999-04-14</DATE> </REFSECT2INFO> <TITLE> Outputs @@ -173,7 +184,7 @@ Operator to use for sorting. <REFSECT1 ID="R1-SQL-CREATEOPERATOR-1"> <REFSECT1INFO> - <DATE>1998-09-09</DATE> + <DATE>1999-04-14</DATE> </REFSECT1INFO> <TITLE> Description @@ -252,9 +263,9 @@ Operator to use for sorting. If a commutator operator name is supplied, <productname>Postgres</productname> searches for it in the catalog. If it is found and it - does not yet have a commutator itself, then the commutator's - entry is updated to have the current (new) operator - as its commutator. This applies to the negator, as well. + does not yet have a commutator itself, then the commutator's + entry is updated to have the newly created operator as its + commutator. This applies to the negator, as well. </para> <para> This is to allow the definition of two operators that are @@ -262,41 +273,34 @@ Operator to use for sorting. operator should be defined without a commutator or negator (as appropriate). When the second operator is defined, name the first as the commutator or negator. The first - will be updated as a side effect. + will be updated as a side effect. (As of Postgres 6.5, + it also works to just have both operators refer to each other.) </para> <para> - The next two specifications are present to support the + The next three specifications are present to support the query optimizer in performing joins. <productname>Postgres</productname> can always evaluate a join (i.e., processing a clause with two tuple variables separated by an operator that returns a boolean) by iterative substitution [WONG76]. In addition, <productname>Postgres</productname> - is planning on implementing a hash-join algorithm along + can use a hash-join algorithm along the lines of [SHAP86]; however, it must know whether this - strategy is applicable. - For example, a hash-join - algorithm is usable for a clause of the form: - <programlisting> - MYBOXES.description === MYBOXES2.description - </programlisting> - but not for a clause of the form: - <programlisting> - MYBOXES.description <<< MYBOXES2.description. - </programlisting> - The HASHES flag gives the needed information to the query - optimizer concerning whether a hash join strategy is - usable for the operator in question.</para> + strategy is applicable. The current hash-join algorithm + is only correct for operators that represent equality tests; + furthermore, equality of the datatype must mean bitwise equality + of the representation of the type. (For example, a datatype that + contains unused bits that don't matter for equality tests could + not be hashjoined.) + The HASHES flag indicates to the query optimizer that a hash join + may safely be used with this operator.</para> <para> Similarly, the two sort operators indicate to the query optimizer whether merge-sort is a usable join strategy and - what operators should be used to sort the two operand - classes. For the === clause above, the optimizer must - sort both relations using the operator, <<<. On the other - hand, merge-sort is not usable with the clause: - <programlisting> - MYBOXES.description <<< MYBOXES2.description - </programlisting> + which operators should be used to sort the two operand + classes. Sort operators should only be provided for an equality + operator, and they should refer to less-than operators for the + left and right side data types respectively. </para> <para> If other join strategies are found to be practical, @@ -355,7 +359,7 @@ Operator to use for sorting. <REFSECT2 ID="R2-SQL-CREATEOPERATOR-3"> <REFSECT2INFO> - <DATE>1998-09-09</DATE> + <DATE>1999-04-14</DATE> </REFSECT2INFO> <TITLE> Notes @@ -385,9 +389,10 @@ Operator to use for sorting. COMMUTATOR = ===, NEGATOR = !==, RESTRICT = area_restriction_procedure, + JOIN = area_join_procedure, HASHES, - JOIN = area-join-procedure, - SORT = <<<, <<<) + SORT1 = <<<, + SORT2 = <<<) </ProgramListing> </REFSECT1> @@ -401,7 +406,7 @@ Operator to use for sorting. <REFSECT2 ID="R2-SQL-CREATEOPERATOR-4"> <REFSECT2INFO> - <DATE>1998-09-09</DATE> + <DATE>1999-04-14</DATE> </REFSECT2INFO> <TITLE> SQL92 |