mirror of https://github.com/postgres/postgres
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
This commit is contained in:
Bruce Momjian
parent
344190b7ef
commit
f45ec44c6b
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@ -7,19 +7,20 @@
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Consequently, while it is possible to define a new
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function without defining a new type, the reverse is
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not true. We therefore describe how to add new functions
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to <ProductName>Postgres</ProductName> before describing how to add new
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types.
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<ProductName>Postgres</ProductName> <Acronym>SQL</Acronym> provides two types of functions: query
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language functions (functions written in <Acronym>SQL</Acronym> and
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programming language functions (functions written in a
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compiled programming language such as <Acronym>C</Acronym>.) Either kind
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to <ProductName>Postgres</ProductName> before describing
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how to add new types.
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<ProductName>Postgres</ProductName> <Acronym>SQL</Acronym>
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provides two types of functions: query language functions
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(functions written in <Acronym>SQL</Acronym> and programming
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language functions (functions written in a compiled
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programming language such as <Acronym>C</Acronym>.) Either kind
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of function can take a base type, a composite type or
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some combination as arguments (parameters). In addition,
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both kinds of functions can return a base type or
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a composite type. It's easier to define <Acronym>SQL</Acronym> functions,
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so we'll start with those.
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Examples in this section can also be found in <FileName>funcs.sql</FileName>
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and <FileName>C-code/funcs.c</FileName>.
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a composite type. It's easier to define <Acronym>SQL</Acronym>
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functions, so we'll start with those. Examples in this section
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can also be found in <FileName>funcs.sql</FileName>
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and <FileName>funcs.c</FileName>.
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</Para>
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<Sect1>
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@ -54,8 +55,8 @@
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instead of one.
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</Para>
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<Para>
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It's almost as easy to define <Acronym>SQL</Acronym> functions that take
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base types as arguments. In the example below, notice
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It's almost as easy to define <Acronym>SQL</Acronym> functions
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that take base types as arguments. In the example below, notice
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how we refer to the arguments within the function as $1
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and $2.
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@ -91,7 +92,8 @@
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SELECT name, double_salary(EMP) AS dream
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FROM EMP
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WHERE EMP.dept = 'toy';
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WHERE EMP.cubicle ~= '(2,1)'::point;
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+-----+-------+
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|name | dream |
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@ -137,7 +139,7 @@
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AS 'SELECT \'None\'::text AS name,
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1000 AS salary,
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25 AS age,
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\'none\'::text AS dept;'
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\'(2,2)\'::point AS cubicle'
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LANGUAGE 'sql';
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</ProgramListing>
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@ -160,8 +162,8 @@ The target list order must be exactly the same as
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</ListItem>
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<ListItem>
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<Para>
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You must typecast the expressions
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(using ::) very carefully or you will see the following error:
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You must typecast the expressions (using ::) very carefully
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or you will see the following error:
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<ProgramListing>
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WARN::function declared to return type EMP does not retrieve (EMP.*)
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@ -202,11 +204,12 @@ The reason why, in general, we must use the function
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</ItemizedList>
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</para>
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<Para>
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Any collection of commands in the <Acronym>SQL</Acronym> query language
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can be packaged together and defined as a function.
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The commands can include updates (i.e., <Acronym>insert</Acronym>, <Acronym>update</Acronym>
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and <Acronym>delete</Acronym>) as well as <Acronym>select</Acronym> queries. However, the
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final command must be a <Acronym>select</Acronym> that returns whatever is
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Any collection of commands in the <Acronym>SQL</Acronym> query
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language can be packaged together and defined as a function.
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The commands can include updates (i.e., <Acronym>insert</Acronym>,
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<Acronym>update</Acronym> and <Acronym>delete</Acronym>) as well
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as <Acronym>select</Acronym> queries. However, the final command
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must be a <Acronym>select</Acronym> that returns whatever is
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specified as the function's returntype.
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<ProgramListing>
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@ -222,6 +225,7 @@ The reason why, in general, we must use the function
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+--+
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|1 |
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+--+
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</ProgramListing>
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</Para>
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</sect2>
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@ -234,12 +238,13 @@ The reason why, in general, we must use the function
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<Title>Programming Language Functions on Base Types</Title>
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<Para>
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Internally, <ProductName>Postgres</ProductName> regards a base type as a "blob of
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memory." The user-defined functions that you define
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over a type in turn define the way that <ProductName>Postgres</ProductName> can
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operate on it. That is, <ProductName>Postgres</ProductName> will only store and
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retrieve the data from disk and use your user-defined
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functions to input, process, and output the data.
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Internally, <ProductName>Postgres</ProductName> regards a
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base type as a "blob of memory." The user-defined
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functions that you define over a type in turn define the
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way that <ProductName>Postgres</ProductName> can operate
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on it. That is, <ProductName>Postgres</ProductName> will
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only store and retrieve the data from disk and use your
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user-defined functions to input, process, and output the data.
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Base types can have one of three internal formats:
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<ItemizedList>
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<ListItem><Para>pass by value, fixed-length</Para>
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@ -254,14 +259,16 @@ The reason why, in general, we must use the function
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<Para>
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By-value types can only be 1, 2 or 4 bytes in length
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(even if your computer supports by-value types of other
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sizes). <ProductName>Postgres</ProductName> itself only passes integer types by
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value. You should be careful to define your types such
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that they will be the same size (in bytes) on all
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architectures. For example, the <Acronym>long</Acronym> type is dangerous
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because it is 4 bytes on some machines and 8 bytes on
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others, whereas <Acronym>int</Acronym> type is 4 bytes on most <Acronym>UNIX</Acronym>
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machines (though not on most personal computers). A
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reasonable implementation of the <Acronym>int4</Acronym> type on <Acronym>UNIX</Acronym>
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sizes). <ProductName>Postgres</ProductName> itself
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only passes integer types by value. You should be careful
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to define your types such that they will be the same
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size (in bytes) on all architectures. For example, the
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<Acronym>long</Acronym> type is dangerous because it
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is 4 bytes on some machines and 8 bytes on others, whereas
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<Acronym>int</Acronym> type is 4 bytes on most
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<Acronym>UNIX</Acronym> machines (though not on most
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personal computers). A reasonable implementation of
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the <Acronym>int4</Acronym> type on <Acronym>UNIX</Acronym>
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machines might be:
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<ProgramListing>
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@ -277,9 +284,10 @@ The reason why, in general, we must use the function
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<ProgramListing>
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/* 16-byte structure, passed by reference */
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typedef struct {
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char data[16];
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} char16;
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typedef struct
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{
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double x, y;
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} Point;
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</ProgramListing>
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</Para>
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@ -308,10 +316,10 @@ The reason why, in general, we must use the function
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<Para>
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Obviously, the data field is not long enough to hold
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all possible strings -- it's impossible to declare such
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a structure in <Acronym>C</Acronym>. When manipulating variable-length
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types, we must be careful to allocate the correct
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amount of memory and initialize the length field. For
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example, if we wanted to store 40 bytes in a text
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a structure in <Acronym>C</Acronym>. When manipulating
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variable-length types, we must be careful to allocate
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the correct amount of memory and initialize the length field.
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For example, if we wanted to store 40 bytes in a text
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structure, we might use a code fragment like this:
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<ProgramListing>
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#include "postgres.h"
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@ -332,23 +340,30 @@ The reason why, in general, we must use the function
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<ProgramListing>
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#include <string.h>
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#include "postgres.h"
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/* By Value */
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int
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add_one(int arg)
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{
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return(arg + 1);
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}
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text *
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concat_text(text *arg1, text *arg2)
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{
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int32 new_text_size = VARSIZE(arg1) + VARSIZE(arg2) - VARHDRSZ;
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text *new_text = (text *) palloc(new_text_size);
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memset((void *) new_text, 0, new_text_size);
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VARSIZE(new_text) = new_text_size;
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strncpy(VARDATA(new_text), VARDATA(arg1), VARSIZE(arg1)-VARHDRSZ);
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strncat(VARDATA(new_text), VARDATA(arg2), VARSIZE(arg2)-VARHDRSZ);
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return (new_text);
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/* By Reference, Fixed Length */
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Point *
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makepoint(Point *pointx, Point *pointy )
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{
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Point *new_point = (Point *) palloc(sizeof(Point));
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new_point->x = pointx->x;
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new_point->y = pointy->y;
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return new_point;
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}
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/* By Reference, Variable Length */
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text *
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copytext(text *t)
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{
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@ -366,6 +381,19 @@ The reason why, in general, we must use the function
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VARSIZE(t)-VARHDRSZ); /* how many bytes */
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return(new_t);
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}
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text *
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concat_text(text *arg1, text *arg2)
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{
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int32 new_text_size = VARSIZE(arg1) + VARSIZE(arg2) - VARHDRSZ;
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text *new_text = (text *) palloc(new_text_size);
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memset((void *) new_text, 0, new_text_size);
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VARSIZE(new_text) = new_text_size;
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strncpy(VARDATA(new_text), VARDATA(arg1), VARSIZE(arg1)-VARHDRSZ);
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strncat(VARDATA(new_text), VARDATA(arg2), VARSIZE(arg2)-VARHDRSZ);
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return (new_text);
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}
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</ProgramListing>
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</Para>
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@ -374,13 +402,16 @@ The reason why, in general, we must use the function
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<ProgramListing>
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CREATE FUNCTION add_one(int4) RETURNS int4
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AS 'PGROOT/tutorial/obj/funcs.so' LANGUAGE 'c';
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AS 'PGROOT/tutorial/funcs.so' LANGUAGE 'c';
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CREATE FUNCTION makepoint(point, point) RETURNS point
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AS 'PGROOT/tutorial/funcs.so' LANGUAGE 'c';
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CREATE FUNCTION concat_text(text, text) RETURNS text
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AS 'PGROOT/tutorial/obj/funcs.so' LANGUAGE 'c';
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AS 'PGROOT/tutorial/funcs.so' LANGUAGE 'c';
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CREATE FUNCTION copytext(text) RETURNS text
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AS 'PGROOT/tutorial/obj/funcs.so' LANGUAGE 'c';
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AS 'PGROOT/tutorial/funcs.so' LANGUAGE 'c';
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</ProgramListing>
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</Para>
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@ -399,11 +430,11 @@ The reason why, in general, we must use the function
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null fields. In addition, composite types that are
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part of an inheritance hierarchy may have different
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fields than other members of the same inheritance hierarchy.
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Therefore, <ProductName>Postgres</ProductName> provides a procedural
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interface for accessing fields of composite types from
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C.
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As <ProductName>Postgres</ProductName> processes a set of instances, each instance
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will be passed into your function as an opaque structure of type <Acronym>TUPLE</Acronym>.
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Therefore, <ProductName>Postgres</ProductName> provides
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a procedural interface for accessing fields of composite types
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from C. As <ProductName>Postgres</ProductName> processes
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a set of instances, each instance will be passed into your
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function as an opaque structure of type <Acronym>TUPLE</Acronym>.
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Suppose we want to write a function to answer the query
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<ProgramListing>
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* SELECT name, c_overpaid(EMP, 1500) AS overpaid
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@ -414,9 +445,10 @@ The reason why, in general, we must use the function
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<ProgramListing>
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#include "postgres.h"
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#include "libpq-fe.h" /* for TUPLE */
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#include "executor/executor.h" /* for GetAttributeByName() */
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bool
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c_overpaid(TUPLE t,/* the current instance of EMP */
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c_overpaid(TupleTableSlot *t, /* the current instance of EMP */
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int4 limit)
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{
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bool isnull = false;
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@ -430,16 +462,17 @@ The reason why, in general, we must use the function
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</Para>
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<Para>
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<Acronym>GetAttributeByName</Acronym> is the <ProductName>Postgres</ProductName> system function that
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<Acronym>GetAttributeByName</Acronym> is the
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<ProductName>Postgres</ProductName> system function that
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returns attributes out of the current instance. It has
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three arguments: the argument of type TUPLE passed into
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the function, the name of the desired attribute, and a
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return parameter that describes whether the attribute
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is null. <Acronym>GetAttributeByName</Acronym> will align data properly
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so you can cast its return value to the desired type.
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For example, if you have an attribute name which is of
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the type name, the <Acronym>GetAttributeByName</Acronym> call would look
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like:
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is null. <Acronym>GetAttributeByName</Acronym> will
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align data properly so you can cast its return value to
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the desired type. For example, if you have an attribute
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name which is of the type name, the <Acronym>GetAttributeByName</Acronym>
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call would look like:
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<ProgramListing>
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char *str;
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...
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@ -448,8 +481,8 @@ The reason why, in general, we must use the function
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</Para>
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<Para>
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The following query lets <ProductName>Postgres</ProductName> know about the
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c_overpaid function:
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The following query lets <ProductName>Postgres</ProductName>
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know about the c_overpaid function:
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<ProgramListing>
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* CREATE FUNCTION c_overpaid(EMP, int4) RETURNS bool
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AS 'PGROOT/tutorial/obj/funcs.so' LANGUAGE 'c';
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@ -470,24 +503,28 @@ The reason why, in general, we must use the function
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We now turn to the more difficult task of writing
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programming language functions. Be warned: this section
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of the manual will not make you a programmer. You must
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have a good understanding of <Acronym>C</Acronym> (including the use of
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pointers and the malloc memory manager) before trying
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to write <Acronym>C</Acronym> functions for use with <ProductName>Postgres</ProductName>.
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While it may be possible to load functions written in
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languages other than <Acronym>C</Acronym> into <ProductName>Postgres</ProductName>, this is often
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difficult (when it is possible at all) because other
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languages, such as <Acronym>FORTRAN</Acronym> and <Acronym>Pascal</Acronym> often do not follow
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the same "calling convention" as <Acronym>C</Acronym>. That is, other
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have a good understanding of <Acronym>C</Acronym>
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(including the use of pointers and the malloc memory manager)
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before trying to write <Acronym>C</Acronym> functions for
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use with <ProductName>Postgres</ProductName>. While it may
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be possible to load functions written in languages other
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than <Acronym>C</Acronym> into <ProductName>Postgres</ProductName>,
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this is often difficult (when it is possible at all)
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because other languages, such as <Acronym>FORTRAN</Acronym>
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and <Acronym>Pascal</Acronym> often do not follow the same
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"calling convention" as <Acronym>C</Acronym>. That is, other
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languages do not pass argument and return values
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between functions in the same way. For this reason, we
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will assume that your programming language functions
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are written in <Acronym>C</Acronym>.
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The basic rules for building <Acronym>C</Acronym> functions are as follows:
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The basic rules for building <Acronym>C</Acronym> functions
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are as follows:
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<ItemizedList>
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<ListItem>
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<Para>
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Most of the header (include) files for <ProductName>Postgres</ProductName>
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Most of the header (include) files for
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<ProductName>Postgres</ProductName>
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should already be installed in
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<FileName>PGROOT/include</FileName> (see Figure 2).
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You should always include
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@ -511,9 +548,11 @@ Most of the header (include) files for <ProductName>Postgres</ProductName>
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</para>
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</ListItem>
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<ListItem>
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<Para> When allocating memory, use the <ProductName>Postgres</ProductName>
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<Para> When allocating memory, use the
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<ProductName>Postgres</ProductName>
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routines palloc and pfree instead of the
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corresponding <Acronym>C</Acronym> library routines malloc and free.
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corresponding <Acronym>C</Acronym> library routines
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malloc and free.
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The memory allocated by palloc will be freed
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automatically at the end of each transaction,
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preventing memory leaks.
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@ -531,15 +570,16 @@ Most of the header (include) files for <ProductName>Postgres</ProductName>
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</Para>
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</ListItem>
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<ListItem>
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<Para> Most of the internal <ProductName>Postgres</ProductName> types are declared
|
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in postgres.h, so it's a good idea to always
|
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include that file as well. Including postgres.h
|
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will also include elog.h and palloc.h for you.
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<Para> Most of the internal <ProductName>Postgres</ProductName>
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types are declared in postgres.h, so it's a good
|
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idea to always include that file as well. Including
|
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postgres.h will also include elog.h and palloc.h for you.
|
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</Para>
|
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</ListItem>
|
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<ListItem>
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<Para> Compiling and loading your object code so that
|
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it can be dynamically loaded into <ProductName>Postgres</ProductName>
|
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it can be dynamically loaded into
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<ProductName>Postgres</ProductName>
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||||
always requires special flags. See Appendix A
|
||||
for a detailed explanation of how to do it for
|
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your particular operating system.
|
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|
|
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Reference in New Issue