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Diffstat (limited to 'doc/src/sgml/xfunc.sgml')
| -rw-r--r-- | doc/src/sgml/xfunc.sgml | 70 |
1 files changed, 13 insertions, 57 deletions
diff --git a/doc/src/sgml/xfunc.sgml b/doc/src/sgml/xfunc.sgml index 783702a6373..f2f379870fa 100644 --- a/doc/src/sgml/xfunc.sgml +++ b/doc/src/sgml/xfunc.sgml @@ -394,8 +394,8 @@ SELECT name, double_salary(emp.*) AS dream <para> Notice the use of the syntax <literal>$1.salary</literal> to select one field of the argument row value. Also notice - how the calling <command>SELECT</> command uses <literal>*</> - to select + how the calling <command>SELECT</> command + uses <replaceable>table_name</><literal>.*</> to select the entire current row of a table as a composite value. The table row can alternatively be referenced using just the table name, like this: @@ -405,6 +405,8 @@ SELECT name, double_salary(emp) AS dream WHERE emp.cubicle ~= point '(2,1)'; </screen> but this usage is deprecated since it's easy to get confused. + (See <xref linkend="rowtypes-usage"> for details about these + two notations for the composite value of a table row.) </para> <para> @@ -479,7 +481,8 @@ $$ LANGUAGE SQL; </para> <para> - We could call this function directly in either of two ways: + We could call this function directly either by using it in + a value expression: <screen> SELECT new_emp(); @@ -487,7 +490,11 @@ SELECT new_emp(); new_emp -------------------------- (None,1000.0,25,"(2,2)") +</screen> + + or by calling it as a table function: +<screen> SELECT * FROM new_emp(); name | salary | age | cubicle @@ -524,12 +531,7 @@ LINE 1: SELECT new_emp().name; </para> <para> - Another option is to use - functional notation for extracting an attribute. The simple way - to explain this is that we can use the - notations <literal><replaceable>attribute</>(<replaceable>table</>)</> - and <literal><replaceable>table</>.<replaceable>attribute</></> - interchangeably. + Another option is to use functional notation for extracting an attribute: <screen> SELECT name(new_emp()); @@ -539,50 +541,10 @@ SELECT name(new_emp()); None </screen> -<screen> --- This is the same as: --- SELECT emp.name AS youngster FROM emp WHERE emp.age < 30; - -SELECT name(emp) AS youngster FROM emp WHERE age(emp) < 30; - - youngster ------------ - Sam - Andy -</screen> + As explained in <xref linkend="rowtypes-usage">, the field notation and + functional notation are equivalent. </para> - <tip> - <para> - The equivalence between functional notation and attribute notation - makes it possible to use functions on composite types to emulate - <quote>computed fields</>. - <indexterm> - <primary>computed field</primary> - </indexterm> - <indexterm> - <primary>field</primary> - <secondary>computed</secondary> - </indexterm> - For example, using the previous definition - for <literal>double_salary(emp)</>, we can write - -<screen> -SELECT emp.name, emp.double_salary FROM emp; -</screen> - - An application using this wouldn't need to be directly aware that - <literal>double_salary</> isn't a real column of the table. - (You can also emulate computed fields with views.) - </para> - - <para> - Because of this behavior, it's unwise to give a function that takes - a single composite-type argument the same name as any of the fields of - that composite type. - </para> - </tip> - <para> Another way to use a function returning a composite type is to pass the result to another function that accepts the correct row type as input: @@ -599,12 +561,6 @@ SELECT getname(new_emp()); (1 row) </screen> </para> - - <para> - Still another way to use a function that returns a composite type is to - call it as a table function, as described in <xref - linkend="xfunc-sql-table-functions">. - </para> </sect2> <sect2 id="xfunc-output-parameters"> |