diff options
Diffstat (limited to 'doc/src/sgml/ref/create_aggregate.sgml')
| -rw-r--r-- | doc/src/sgml/ref/create_aggregate.sgml | 16 |
1 files changed, 14 insertions, 2 deletions
diff --git a/doc/src/sgml/ref/create_aggregate.sgml b/doc/src/sgml/ref/create_aggregate.sgml index eaa410bc94c..4bda23ada69 100644 --- a/doc/src/sgml/ref/create_aggregate.sgml +++ b/doc/src/sgml/ref/create_aggregate.sgml @@ -27,6 +27,7 @@ CREATE AGGREGATE <replaceable class="parameter">name</replaceable> ( [ <replacea [ , SSPACE = <replaceable class="PARAMETER">state_data_size</replaceable> ] [ , FINALFUNC = <replaceable class="PARAMETER">ffunc</replaceable> ] [ , FINALFUNC_EXTRA ] + [ , COMBINEFUNC = <replaceable class="PARAMETER">combinefunc</replaceable> ] [ , INITCOND = <replaceable class="PARAMETER">initial_condition</replaceable> ] [ , MSFUNC = <replaceable class="PARAMETER">msfunc</replaceable> ] [ , MINVFUNC = <replaceable class="PARAMETER">minvfunc</replaceable> ] @@ -45,6 +46,7 @@ CREATE AGGREGATE <replaceable class="parameter">name</replaceable> ( [ [ <replac [ , SSPACE = <replaceable class="PARAMETER">state_data_size</replaceable> ] [ , FINALFUNC = <replaceable class="PARAMETER">ffunc</replaceable> ] [ , FINALFUNC_EXTRA ] + [ , COMBINEFUNC = <replaceable class="PARAMETER">combinefunc</replaceable> ] [ , INITCOND = <replaceable class="PARAMETER">initial_condition</replaceable> ] [ , HYPOTHETICAL ] ) @@ -58,6 +60,7 @@ CREATE AGGREGATE <replaceable class="PARAMETER">name</replaceable> ( [ , SSPACE = <replaceable class="PARAMETER">state_data_size</replaceable> ] [ , FINALFUNC = <replaceable class="PARAMETER">ffunc</replaceable> ] [ , FINALFUNC_EXTRA ] + [ , COMBINEFUNC = <replaceable class="PARAMETER">combinefunc</replaceable> ] [ , INITCOND = <replaceable class="PARAMETER">initial_condition</replaceable> ] [ , MSFUNC = <replaceable class="PARAMETER">msfunc</replaceable> ] [ , MINVFUNC = <replaceable class="PARAMETER">minvfunc</replaceable> ] @@ -105,12 +108,15 @@ CREATE AGGREGATE <replaceable class="PARAMETER">name</replaceable> ( functions: a state transition function <replaceable class="PARAMETER">sfunc</replaceable>, - and an optional final calculation function - <replaceable class="PARAMETER">ffunc</replaceable>. + an optional final calculation function + <replaceable class="PARAMETER">ffunc</replaceable>, + and an optional combine function + <replaceable class="PARAMETER">combinefunc</replaceable>. These are used as follows: <programlisting> <replaceable class="PARAMETER">sfunc</replaceable>( internal-state, next-data-values ) ---> next-internal-state <replaceable class="PARAMETER">ffunc</replaceable>( internal-state ) ---> aggregate-value +<replaceable class="PARAMETER">combinefunc</replaceable>( internal-state, internal-state ) ---> next-internal-state </programlisting> </para> @@ -128,6 +134,12 @@ CREATE AGGREGATE <replaceable class="PARAMETER">name</replaceable> ( </para> <para> + An aggregate function may also supply a combining function, which allows + the aggregation process to be broken down into multiple steps. This + facilitates query optimization techniques such as parallel query. + </para> + + <para> An aggregate function can provide an initial condition, that is, an initial value for the internal state value. This is specified and stored in the database as a value of type |