1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
|
<REFENTRY ID="SQL-CREATEAGGREGATE-1">
<REFMETA>
<REFENTRYTITLE>
CREATE AGGREGATE
</REFENTRYTITLE>
<REFMISCINFO>SQL - Language Statements</REFMISCINFO>
</REFMETA>
<comment>This entry needs a lot of work, especially some
usefully complex examples. Since I don't yet understand it, I
haven't done this.</comment>
<REFNAMEDIV>
<REFNAME>
CREATE AGGREGATE
</REFNAME>
<REFPURPOSE>
Defines a new aggregate function
</REFPURPOSE>
<REFSYNOPSISDIV>
<REFSYNOPSISDIVINFO>
<DATE>1998-04-15</DATE>
</REFSYNOPSISDIVINFO>
<SYNOPSIS>
CREATE AGGREGATE <REPLACEABLE CLASS="PARAMETER">name</REPLACEABLE> [AS]
([ SFUNC1 = <REPLACEABLE CLASS="PARAMETER">state_transition_function1</REPLACEABLE>
, BASETYPE = <REPLACEABLE CLASS="PARAMETER">data_type</REPLACEABLE>
, STYPE1 = <REPLACEABLE CLASS="PARAMETER">sfunc1_return_type</REPLACEABLE> ]
[, SFUNC2 = <REPLACEABLE CLASS="PARAMETER">state_transition_function2</REPLACEABLE>
, STYPE2 = <REPLACEABLE CLASS="PARAMETER">sfunc2_return_type</REPLACEABLE> ]
[, FINALFUNC = <REPLACEABLE CLASS="PARAMETER">final_function</REPLACEABLE> ]
[, INITCOND1 = <REPLACEABLE CLASS="PARAMETER">initial_condition1</REPLACEABLE> ]
[, INITCOND2 = <REPLACEABLE CLASS="PARAMETER">initial_condition2</REPLACEABLE> ]
)
</SYNOPSIS>
<REFSECT2 ID="R2-SQL-CREATEAGGREGATE-1">
<REFSECT2INFO>
<DATE>1998-04-15</DATE>
</REFSECT2INFO>
<TITLE>
Inputs
</TITLE>
<variablelist>
<varlistentry>
<term></term>
<listitem>
<PARA>
<VARIABLELIST>
<VARLISTENTRY>
<TERM>
<REPLACEABLE CLASS="PARAMETER">name</REPLACEABLE>
</TERM>
<LISTITEM>
<para>
The name of an aggregate function to create.
</para>
</LISTITEM>
</varlistentry>
<varlistentry>
<term>
<REPLACEABLE CLASS="PARAMETER">state_transition_function1</REPLACEABLE>
</term>
<listitem>
<para>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<REPLACEABLE CLASS="PARAMETER">data_type</REPLACEABLE>
</term>
<listitem>
<para>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<REPLACEABLE CLASS="PARAMETER">sfunc1_return_type</REPLACEABLE>
</term>
<listitem>
<para>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<REPLACEABLE CLASS="PARAMETER">state-transition_function2</REPLACEABLE>
</term>
<listitem>
<para>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<REPLACEABLE CLASS="PARAMETER">sfunc2_return_type</REPLACEABLE>
</term>
<listitem>
<para>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<REPLACEABLE CLASS="PARAMETER">final_function</REPLACEABLE>
</term>
<listitem>
<para>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<REPLACEABLE CLASS="PARAMETER">initial_condition1</REPLACEABLE>
</term>
<listitem>
<para>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<REPLACEABLE CLASS="PARAMETER">initial_condition2</REPLACEABLE>
</term>
<listitem>
<para>
</para>
</listitem>
</varlistentry>
</variablelist>
</PARA>
</listitem>
</varlistentry>
</variablelist>
</REFSECT2>
<REFSECT2 ID="R2-SQL-CREATEAGGREGATE-2">
<REFSECT2INFO>
<DATE>1998-04-15</DATE>
</REFSECT2INFO>
<TITLE>
Outputs
</TITLE>
<PARA>
</PARA>
<VARIABLELIST>
<VARLISTENTRY>
<TERM>
</TERM>
<LISTITEM>
<PARA>
<VARIABLELIST>
<VARLISTENTRY>
<TERM>
<ReturnValue>CREATE</ReturnValue>
</TERM>
<LISTITEM>
<PARA>
Message returned if the command completes successfully.
</PARA>
</LISTITEM>
</VARLISTENTRY>
</VARIABLELIST>
</LISTITEM>
</VARLISTENTRY>
</VARIABLELIST>
</REFSECT2>
</REFSYNOPSISDIV>
<REFSECT1 ID="R1-SQL-CREATEAGGREGATE-1">
<REFSECT1INFO>
<DATE>1998-04-15</DATE>
</REFSECT1INFO>
<TITLE>
Description
</TITLE>
<PARA>
An aggregate function can use up to three functions, two
state transition functions, X1 and X2:
X1( internal-state1, next-data_item ) ---> next-internal-state1
X2( internal-state2 ) ---> next-internal-state2
and a final calculation function, F:
F(internal-state1, internal-state2) ---> aggregate-value
These functions are required to have the following properties:
<itemizedlist>
<listitem>
<para>
The arguments to state-transition-function-1 must
be (stype1,basetype), and its return value must be
stype1.
</para>
</listitem>
<listitem>
<para>
The argument and return value of state-transition-
function-2 must be stype2.
</para>
</listitem>
<listitem>
<para>
The arguments to the final-calculation-function
must be (stype1,stype2), and its return value must
be a POSTGRES base type (not necessarily the same
as basetype.
</para>
</listitem>
<listitem>
<para>
The final-calculation-function should be specified
if and only if both state-transition functions are
specified.
</para
</listitem>
</itemizedlist>
</PARA>
<para>
Note that it is possible to specify aggregate functions
that have varying combinations of state and final functions.
For example, the "count" aggregate requires sfunc2
(an incrementing function) but not sfunc1 or finalfunc,
whereas the "sum" aggregate requires sfunc1 (an addition
function) but not sfunc2 or finalfunc and the "average"
aggregate requires both of the above state functions as
well as a finalfunc (a division function) to produce its
answer. In any case, at least one state function must be
defined, and any sfunc2 must have a corresponding initcond2.
</para>
<para>
Aggregates also require two initial conditions, one for
each transition function. These are specified and stored
in the database as fields of type text.
</para>
<REFSECT2 ID="R2-SQL-CREATEAGGREGATE-3">
<REFSECT2INFO>
<DATE>1998-04-15</DATE>
</REFSECT2INFO>
<TITLE>
Notes
</TITLE>
<PARA>
CREATE AGGREGATE function is a PostgreSQL language extension.
</PARA>
<para>
Refer to DROP AGGREGATE function to drop aggregate functions.
</para>
</REFSECT2>
<REFSECT1 ID="R1-SQL-CREATEAGGREGATE-2">
<TITLE>
Usage
</TITLE>
<PARA>
</PARA>
<ProgramListing>
</ProgramListing>
</REFSECT1>
<REFSECT1 ID="R1-SQL-CREATEAGGREGATE-3">
<TITLE>
Compatibility
</TITLE>
<PARA>
</PARA>
<REFSECT2 ID="R2-SQL-CREATEAGGREGATE-4">
<REFSECT2INFO>
<DATE>1998-04-15</DATE>
</REFSECT2INFO>
<TITLE>
SQL92
</TITLE>
<PARA>
There is no CREATE AGGREGATE function on SQL92.
</PARA>
</REFENTRY>
<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:t
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
sgml-parent-document:nil
sgml-default-dtd-file:"../reference.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:"/usr/lib/sgml/catalog"
sgml-local-ecat-files:nil
End:
-->
|
