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提交 f45ec44c 编写于 作者: B Bruce Momjian
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Patches for the SGML documentation relating 

to the tutorial code changes.

NOTE:  I couldn't get ngsmls to find the document
type so that the changes could be checked.  However,
the changes were very minor:

Best,

Clark
上级 344190b7
隐藏空白更改
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Showing with 133 addition and 93 deletion
doc/src/sgml/xfunc.sgml
浏览文件 @ f45ec44c
......@@ -7,19 +7,20 @@
Consequently, while it is possible to define a new
function without defining a new type, the reverse is
not true. We therefore describe how to add new functions
to <ProductName>Postgres</ProductName> before describing how to add new
types.
<ProductName>Postgres</ProductName> <Acronym>SQL</Acronym> provides two types of functions: query
language functions (functions written in <Acronym>SQL</Acronym> and
programming language functions (functions written in a
compiled programming language such as <Acronym>C</Acronym>.) Either kind
to <ProductName>Postgres</ProductName> before describing
how to add new types.
<ProductName>Postgres</ProductName> <Acronym>SQL</Acronym>
provides two types of functions: query language functions
(functions written in <Acronym>SQL</Acronym> and programming
language functions (functions written in a compiled
programming language such as <Acronym>C</Acronym>.) Either kind
of function can take a base type, a composite type or
some combination as arguments (parameters). In addition,
both kinds of functions can return a base type or
a composite type. It's easier to define <Acronym>SQL</Acronym> functions,
so we'll start with those.
Examples in this section can also be found in <FileName>funcs.sql</FileName>
and <FileName>C-code/funcs.c</FileName>.
a composite type. It's easier to define <Acronym>SQL</Acronym>
functions, so we'll start with those. Examples in this section
can also be found in <FileName>funcs.sql</FileName>
and <FileName>funcs.c</FileName>.
</Para>
<Sect1>
......@@ -54,8 +55,8 @@
instead of one.
</Para>
<Para>
It's almost as easy to define <Acronym>SQL</Acronym> functions that take
base types as arguments. In the example below, notice
It's almost as easy to define <Acronym>SQL</Acronym> functions
that take base types as arguments. In the example below, notice
how we refer to the arguments within the function as $1
and $2.
......@@ -91,7 +92,8 @@
SELECT name, double_salary(EMP) AS dream
FROM EMP
WHERE EMP.dept = 'toy';
WHERE EMP.cubicle ~= '(2,1)'::point;
+-----+-------+
|name | dream |
......@@ -137,7 +139,7 @@
AS 'SELECT \'None\'::text AS name,
1000 AS salary,
25 AS age,
\'none\'::text AS dept;'
\'(2,2)\'::point AS cubicle'
LANGUAGE 'sql';
</ProgramListing>
......@@ -153,18 +155,18 @@
<ItemizedList>
<ListItem>
<Para>
The target list order must be exactly the same as
that in which the attributes appear in the CREATE
TABLE statement (or when you execute a .* query).
The target list order must be exactly the same as
that in which the attributes appear in the CREATE
TABLE statement (or when you execute a .* query).
</Para>
</ListItem>
<ListItem>
<Para>
You must typecast the expressions
(using ::) very carefully or you will see the following error:
You must typecast the expressions (using ::) very carefully
or you will see the following error:
<ProgramListing>
WARN::function declared to return type EMP does not retrieve (EMP.*)
WARN::function declared to return type EMP does not retrieve (EMP.*)
</ProgramListing>
</Para>
</ListItem>
......@@ -202,11 +204,12 @@ The reason why, in general, we must use the function
</ItemizedList>
</para>
<Para>
Any collection of commands in the <Acronym>SQL</Acronym> query language
can be packaged together and defined as a function.
The commands can include updates (i.e., <Acronym>insert</Acronym>, <Acronym>update</Acronym>
and <Acronym>delete</Acronym>) as well as <Acronym>select</Acronym> queries. However, the
final command must be a <Acronym>select</Acronym> that returns whatever is
Any collection of commands in the <Acronym>SQL</Acronym> query
language can be packaged together and defined as a function.
The commands can include updates (i.e., <Acronym>insert</Acronym>,
<Acronym>update</Acronym> and <Acronym>delete</Acronym>) as well
as <Acronym>select</Acronym> queries. However, the final command
must be a <Acronym>select</Acronym> that returns whatever is
specified as the function's returntype.
<ProgramListing>
......@@ -222,6 +225,7 @@ The reason why, in general, we must use the function
+--+
|1 |
+--+
</ProgramListing>
</Para>
</sect2>
......@@ -234,12 +238,13 @@ The reason why, in general, we must use the function
<Title>Programming Language Functions on Base Types</Title>
<Para>
Internally, <ProductName>Postgres</ProductName> regards a base type as a "blob of
memory." The user-defined functions that you define
over a type in turn define the way that <ProductName>Postgres</ProductName> can
operate on it. That is, <ProductName>Postgres</ProductName> will only store and
retrieve the data from disk and use your user-defined
functions to input, process, and output the data.
Internally, <ProductName>Postgres</ProductName> regards a
base type as a "blob of memory." The user-defined
functions that you define over a type in turn define the
way that <ProductName>Postgres</ProductName> can operate
on it. That is, <ProductName>Postgres</ProductName> will
only store and retrieve the data from disk and use your
user-defined functions to input, process, and output the data.
Base types can have one of three internal formats:
<ItemizedList>
<ListItem><Para>pass by value, fixed-length</Para>
......@@ -254,14 +259,16 @@ The reason why, in general, we must use the function
<Para>
By-value types can only be 1, 2 or 4 bytes in length
(even if your computer supports by-value types of other
sizes). <ProductName>Postgres</ProductName> itself only passes integer types by
value. You should be careful to define your types such
that they will be the same size (in bytes) on all
architectures. For example, the <Acronym>long</Acronym> type is dangerous
because it is 4 bytes on some machines and 8 bytes on
others, whereas <Acronym>int</Acronym> type is 4 bytes on most <Acronym>UNIX</Acronym>
machines (though not on most personal computers). A
reasonable implementation of the <Acronym>int4</Acronym> type on <Acronym>UNIX</Acronym>
sizes). <ProductName>Postgres</ProductName> itself
only passes integer types by value. You should be careful
to define your types such that they will be the same
size (in bytes) on all architectures. For example, the
<Acronym>long</Acronym> type is dangerous because it
is 4 bytes on some machines and 8 bytes on others, whereas
<Acronym>int</Acronym> type is 4 bytes on most
<Acronym>UNIX</Acronym> machines (though not on most
personal computers). A reasonable implementation of
the <Acronym>int4</Acronym> type on <Acronym>UNIX</Acronym>
machines might be:
<ProgramListing>
......@@ -277,9 +284,10 @@ The reason why, in general, we must use the function
<ProgramListing>
/* 16-byte structure, passed by reference */
typedef struct {
char data[16];
} char16;
typedef struct
{
double x, y;
} Point;
</ProgramListing>
</Para>
......@@ -308,10 +316,10 @@ The reason why, in general, we must use the function
<Para>
Obviously, the data field is not long enough to hold
all possible strings -- it's impossible to declare such
a structure in <Acronym>C</Acronym>. When manipulating variable-length
types, we must be careful to allocate the correct
amount of memory and initialize the length field. For
example, if we wanted to store 40 bytes in a text
a structure in <Acronym>C</Acronym>. When manipulating
variable-length types, we must be careful to allocate
the correct amount of memory and initialize the length field.
For example, if we wanted to store 40 bytes in a text
structure, we might use a code fragment like this:
<ProgramListing>
#include "postgres.h"
......@@ -332,23 +340,30 @@ The reason why, in general, we must use the function
<ProgramListing>
#include &lt;string.h&gt;
#include "postgres.h"
/* By Value */
int
add_one(int arg)
{
return(arg + 1);
}
text *
concat_text(text *arg1, text *arg2)
/* By Reference, Fixed Length */
Point *
makepoint(Point *pointx, Point *pointy )
{
int32 new_text_size = VARSIZE(arg1) + VARSIZE(arg2) - VARHDRSZ;
text *new_text = (text *) palloc(new_text_size);
memset((void *) new_text, 0, new_text_size);
VARSIZE(new_text) = new_text_size;
strncpy(VARDATA(new_text), VARDATA(arg1), VARSIZE(arg1)-VARHDRSZ);
strncat(VARDATA(new_text), VARDATA(arg2), VARSIZE(arg2)-VARHDRSZ);
return (new_text);
Point *new_point = (Point *) palloc(sizeof(Point));
new_point->x = pointx->x;
new_point->y = pointy->y;
return new_point;
}
/* By Reference, Variable Length */
text *
copytext(text *t)
{
......@@ -366,6 +381,19 @@ The reason why, in general, we must use the function
VARSIZE(t)-VARHDRSZ); /* how many bytes */
return(new_t);
}
text *
concat_text(text *arg1, text *arg2)
{
int32 new_text_size = VARSIZE(arg1) + VARSIZE(arg2) - VARHDRSZ;
text *new_text = (text *) palloc(new_text_size);
memset((void *) new_text, 0, new_text_size);
VARSIZE(new_text) = new_text_size;
strncpy(VARDATA(new_text), VARDATA(arg1), VARSIZE(arg1)-VARHDRSZ);
strncat(VARDATA(new_text), VARDATA(arg2), VARSIZE(arg2)-VARHDRSZ);
return (new_text);
}
</ProgramListing>
</Para>
......@@ -374,13 +402,16 @@ The reason why, in general, we must use the function
<ProgramListing>
CREATE FUNCTION add_one(int4) RETURNS int4
AS 'PGROOT/tutorial/obj/funcs.so' LANGUAGE 'c';
AS 'PGROOT/tutorial/funcs.so' LANGUAGE 'c';
CREATE FUNCTION makepoint(point, point) RETURNS point
AS 'PGROOT/tutorial/funcs.so' LANGUAGE 'c';
CREATE FUNCTION concat_text(text, text) RETURNS text
AS 'PGROOT/tutorial/obj/funcs.so' LANGUAGE 'c';
AS 'PGROOT/tutorial/funcs.so' LANGUAGE 'c';
CREATE FUNCTION copytext(text) RETURNS text
AS 'PGROOT/tutorial/obj/funcs.so' LANGUAGE 'c';
AS 'PGROOT/tutorial/funcs.so' LANGUAGE 'c';
</ProgramListing>
</Para>
......@@ -399,11 +430,11 @@ The reason why, in general, we must use the function
null fields. In addition, composite types that are
part of an inheritance hierarchy may have different
fields than other members of the same inheritance hierarchy.
Therefore, <ProductName>Postgres</ProductName> provides a procedural
interface for accessing fields of composite types from
C.
As <ProductName>Postgres</ProductName> processes a set of instances, each instance
will be passed into your function as an opaque structure of type <Acronym>TUPLE</Acronym>.
Therefore, <ProductName>Postgres</ProductName> provides
a procedural interface for accessing fields of composite types
from C. As <ProductName>Postgres</ProductName> processes
a set of instances, each instance will be passed into your
function as an opaque structure of type <Acronym>TUPLE</Acronym>.
Suppose we want to write a function to answer the query
<ProgramListing>
* SELECT name, c_overpaid(EMP, 1500) AS overpaid
......@@ -414,9 +445,10 @@ The reason why, in general, we must use the function
<ProgramListing>
#include "postgres.h"
#include "libpq-fe.h" /* for TUPLE */
#include "executor/executor.h" /* for GetAttributeByName() */
bool
c_overpaid(TUPLE t,/* the current instance of EMP */
c_overpaid(TupleTableSlot *t, /* the current instance of EMP */
int4 limit)
{
bool isnull = false;
......@@ -430,16 +462,17 @@ The reason why, in general, we must use the function
</Para>
<Para>
<Acronym>GetAttributeByName</Acronym> is the <ProductName>Postgres</ProductName> system function that
<Acronym>GetAttributeByName</Acronym> is the
<ProductName>Postgres</ProductName> system function that
returns attributes out of the current instance. It has
three arguments: the argument of type TUPLE passed into
the function, the name of the desired attribute, and a
return parameter that describes whether the attribute
is null. <Acronym>GetAttributeByName</Acronym> will align data properly
so you can cast its return value to the desired type.
For example, if you have an attribute name which is of
the type name, the <Acronym>GetAttributeByName</Acronym> call would look
like:
is null. <Acronym>GetAttributeByName</Acronym> will
align data properly so you can cast its return value to
the desired type. For example, if you have an attribute
name which is of the type name, the <Acronym>GetAttributeByName</Acronym>
call would look like:
<ProgramListing>
char *str;
...
......@@ -448,8 +481,8 @@ The reason why, in general, we must use the function
</Para>
<Para>
The following query lets <ProductName>Postgres</ProductName> know about the
c_overpaid function:
The following query lets <ProductName>Postgres</ProductName>
know about the c_overpaid function:
<ProgramListing>
* CREATE FUNCTION c_overpaid(EMP, int4) RETURNS bool
AS 'PGROOT/tutorial/obj/funcs.so' LANGUAGE 'c';
......@@ -470,24 +503,28 @@ The reason why, in general, we must use the function
We now turn to the more difficult task of writing
programming language functions. Be warned: this section
of the manual will not make you a programmer. You must
have a good understanding of <Acronym>C</Acronym> (including the use of
pointers and the malloc memory manager) before trying
to write <Acronym>C</Acronym> functions for use with <ProductName>Postgres</ProductName>.
While it may be possible to load functions written in
languages other than <Acronym>C</Acronym> into <ProductName>Postgres</ProductName>, this is often
difficult (when it is possible at all) because other
languages, such as <Acronym>FORTRAN</Acronym> and <Acronym>Pascal</Acronym> often do not follow
the same "calling convention" as <Acronym>C</Acronym>. That is, other
have a good understanding of <Acronym>C</Acronym>
(including the use of pointers and the malloc memory manager)
before trying to write <Acronym>C</Acronym> functions for
use with <ProductName>Postgres</ProductName>. While it may
be possible to load functions written in languages other
than <Acronym>C</Acronym> into <ProductName>Postgres</ProductName>,
this is often difficult (when it is possible at all)
because other languages, such as <Acronym>FORTRAN</Acronym>
and <Acronym>Pascal</Acronym> often do not follow the same
"calling convention" as <Acronym>C</Acronym>. That is, other
languages do not pass argument and return values
between functions in the same way. For this reason, we
will assume that your programming language functions
are written in <Acronym>C</Acronym>.
The basic rules for building <Acronym>C</Acronym> functions are as follows:
The basic rules for building <Acronym>C</Acronym> functions
are as follows:
<ItemizedList>
<ListItem>
<Para>
Most of the header (include) files for <ProductName>Postgres</ProductName>
Most of the header (include) files for
<ProductName>Postgres</ProductName>
should already be installed in
<FileName>PGROOT/include</FileName> (see Figure 2).
You should always include
......@@ -511,9 +548,11 @@ Most of the header (include) files for <ProductName>Postgres</ProductName>
</para>
</ListItem>
<ListItem>
<Para> When allocating memory, use the <ProductName>Postgres</ProductName>
<Para> When allocating memory, use the
<ProductName>Postgres</ProductName>
routines palloc and pfree instead of the
corresponding <Acronym>C</Acronym> library routines malloc and free.
corresponding <Acronym>C</Acronym> library routines
malloc and free.
The memory allocated by palloc will be freed
automatically at the end of each transaction,
preventing memory leaks.
......@@ -531,15 +570,16 @@ Most of the header (include) files for <ProductName>Postgres</ProductName>
</Para>
</ListItem>
<ListItem>
<Para> Most of the internal <ProductName>Postgres</ProductName> types are declared
in postgres.h, so it's a good idea to always
include that file as well. Including postgres.h
will also include elog.h and palloc.h for you.
<Para> Most of the internal <ProductName>Postgres</ProductName>
types are declared in postgres.h, so it's a good
idea to always include that file as well. Including
postgres.h will also include elog.h and palloc.h for you.
</Para>
</ListItem>
<ListItem>
<Para> Compiling and loading your object code so that
it can be dynamically loaded into <ProductName>Postgres</ProductName>
<Para> Compiling and loading your object code so that
it can be dynamically loaded into
<ProductName>Postgres</ProductName>
always requires special flags. See Appendix A
for a detailed explanation of how to do it for
your particular operating system.
......
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