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As discussed on several occasions previously, the new anonymous

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composite type capability makes it possible to create a system view
based on a table function in a way that is hopefully palatable to
everyone. The attached patch takes advantage of this, moving
show_all_settings() from contrib/tablefunc into the backend (renamed
all_settings(). It is defined as a builtin returning type RECORD. During
initdb a system view is created to expose the same information presently
available through SHOW ALL. For example:

test=# select * from pg_settings where name like '%debug%';
          name          | setting
-----------------------+---------
  debug_assertions      | on
  debug_pretty_print    | off
  debug_print_parse     | off
  debug_print_plan      | off
  debug_print_query     | off
  debug_print_rewritten | off
  wal_debug             | 0
(7 rows)


Additionally during initdb two rules are created which make it possible
to change settings by updating the system view -- a "virtual table" as
Tom put it. Here's an example:

Joe Conway
This commit is contained in:
Bruce Momjian
2002-08-15 02:51:27 +00:00
parent 4c4854c458
commit 45e2544584
10 changed files with 372 additions and 220 deletions
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139
contrib/tablefunc/README.tablefunc
View File

@ -46,9 +46,6 @@ Installation:
installs following functions into database template1:
show_all_settings()
- returns the same information as SHOW ALL, but as a query result
normal_rand(int numvals, float8 mean, float8 stddev, int seed)
- returns a set of normally distributed float8 values
@ -58,48 +55,15 @@ Installation:
but you can create additional crosstab functions per the instructions
in the documentation below.
crosstab(text sql, N int)
- returns a set of row_name plus N category value columns
- requires anonymous composite type syntax in the FROM clause. See
the instructions in the documentation below.
Documentation
==================================================================
Name
show_all_settings() - returns the same information as SHOW ALL,
but as a query result.
Synopsis
show_all_settings()
Inputs
none
Outputs
Returns setof tablefunc_config_settings which is defined by:
CREATE VIEW tablefunc_config_settings AS
SELECT
''::TEXT AS name,
''::TEXT AS setting;
Example usage
test=# select * from show_all_settings();
name | setting
-------------------------------+---------------------------------------
australian_timezones | off
authentication_timeout | 60
checkpoint_segments | 3
.
.
.
wal_debug | 0
wal_files | 0
wal_sync_method | fdatasync
(94 rows)
==================================================================
Name
normal_rand(int, float8, float8, int) - returns a set of normally
distributed float8 values
@ -267,6 +231,99 @@ select * from crosstab3(
test2 | val6 | val7 |
(2 rows)
==================================================================
Name
crosstab(text, int) - returns a set of row_name
plus N category value columns
Synopsis
crosstab(text sql, int N)
Inputs
sql
A SQL statement which produces the source set of data. The SQL statement
must return one row_name column, one category column, and one value
column.
e.g. provided sql must produce a set something like:
row_name cat value
----------+-------+-------
row1 cat1 val1
row1 cat2 val2
row1 cat3 val3
row1 cat4 val4
row2 cat1 val5
row2 cat2 val6
row2 cat3 val7
row2 cat4 val8
N
number of category value columns
Outputs
Returns setof record, which must defined with a column definition
in the FROM clause of the SELECT statement, e.g.:
SELECT *
FROM crosstab(sql, 2) AS ct(row_name text, category_1 text, category_2 text);
the example crosstab function produces a set something like:
<== values columns ==>
row_name category_1 category_2
---------+------------+------------
row1 val1 val2
row2 val5 val6
Notes
1. The sql result must be ordered by 1,2.
2. The number of values columns is determined at run-time. The
column definition provided in the FROM clause must provide for
N + 1 columns of the proper data types.
3. Missing values (i.e. not enough adjacent rows of same row_name to
fill the number of result values columns) are filled in with nulls.
4. Extra values (i.e. too many adjacent rows of same row_name to fill
the number of result values columns) are skipped.
5. Rows with all nulls in the values columns are skipped.
Example usage
create table ct(id serial, rowclass text, rowid text, attribute text, value text);
insert into ct(rowclass, rowid, attribute, value) values('group1','test1','att1','val1');
insert into ct(rowclass, rowid, attribute, value) values('group1','test1','att2','val2');
insert into ct(rowclass, rowid, attribute, value) values('group1','test1','att3','val3');
insert into ct(rowclass, rowid, attribute, value) values('group1','test1','att4','val4');
insert into ct(rowclass, rowid, attribute, value) values('group1','test2','att1','val5');
insert into ct(rowclass, rowid, attribute, value) values('group1','test2','att2','val6');
insert into ct(rowclass, rowid, attribute, value) values('group1','test2','att3','val7');
insert into ct(rowclass, rowid, attribute, value) values('group1','test2','att4','val8');
SELECT *
FROM crosstab(
'select rowid, attribute, value
from ct
where rowclass = ''group1''
and (attribute = ''att2'' or attribute = ''att3'') order by 1,2;', 3)
AS ct(row_name text, category_1 text, category_2 text, category_3 text);
row_name | category_1 | category_2 | category_3
----------+------------+------------+------------
test1 | val2 | val3 |
test2 | val6 | val7 |
(2 rows)
==================================================================
-- Joe Conway