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As discussed on several occasions previously, the new anonymous
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
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‎contrib/tablefunc/README.tablefunc

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@@ -46,9 +46,6 @@ Installation:
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installs following functions into database template1:
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show_all_settings()
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- returns the same information as SHOW ALL, but as a query result
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normal_rand(int numvals, float8 mean, float8 stddev, int seed)
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- returns a set of normally distributed float8 values
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@@ -58,45 +55,12 @@ Installation:
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but you can create additional crosstab functions per the instructions
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in the documentation below.
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Documentation
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==================================================================
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Name
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show_all_settings() - returns the same information as SHOW ALL,
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but as a query result.
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Synopsis
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show_all_settings()
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Inputs
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none
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Outputs
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Returns setof tablefunc_config_settings which is defined by:
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CREATE VIEW tablefunc_config_settings AS
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SELECT
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''::TEXT AS name,
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''::TEXT AS setting;
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Example usage
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test=# select * from show_all_settings();
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name | setting
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-------------------------------+---------------------------------------
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australian_timezones | off
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authentication_timeout | 60
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checkpoint_segments | 3
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.
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.
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.
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wal_debug | 0
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wal_files | 0
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wal_sync_method | fdatasync
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(94 rows)
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crosstab(text sql, N int)
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- returns a set of row_name plus N category value columns
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- requires anonymous composite type syntax in the FROM clause. See
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the instructions in the documentation below.
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Documentation
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==================================================================
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Name
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test2 | val6 | val7 |
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(2 rows)
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==================================================================
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Name
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crosstab(text, int) - returns a set of row_name
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plus N category value columns
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Synopsis
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crosstab(text sql, int N)
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Inputs
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sql
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A SQL statement which produces the source set of data. The SQL statement
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must return one row_name column, one category column, and one value
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column.
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e.g. provided sql must produce a set something like:
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row_name cat value
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----------+-------+-------
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row1 cat1 val1
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row1 cat2 val2
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row1 cat3 val3
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row1 cat4 val4
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row2 cat1 val5
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row2 cat2 val6
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row2 cat3 val7
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row2 cat4 val8
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N
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number of category value columns
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Outputs
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Returns setof record, which must defined with a column definition
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in the FROM clause of the SELECT statement, e.g.:
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SELECT *
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FROM crosstab(sql, 2) AS ct(row_name text, category_1 text, category_2 text);
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the example crosstab function produces a set something like:
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<== values columns ==>
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row_name category_1 category_2
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---------+------------+------------
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row1 val1 val2
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row2 val5 val6
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Notes
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1. The sql result must be ordered by 1,2.
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2. The number of values columns is determined at run-time. The
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column definition provided in the FROM clause must provide for
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N + 1 columns of the proper data types.
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3. Missing values (i.e. not enough adjacent rows of same row_name to
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fill the number of result values columns) are filled in with nulls.
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4. Extra values (i.e. too many adjacent rows of same row_name to fill
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the number of result values columns) are skipped.
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5. Rows with all nulls in the values columns are skipped.
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Example usage
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create table ct(id serial, rowclass text, rowid text, attribute text, value text);
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insert into ct(rowclass, rowid, attribute, value) values('group1','test1','att1','val1');
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insert into ct(rowclass, rowid, attribute, value) values('group1','test1','att2','val2');
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insert into ct(rowclass, rowid, attribute, value) values('group1','test1','att3','val3');
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insert into ct(rowclass, rowid, attribute, value) values('group1','test1','att4','val4');
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insert into ct(rowclass, rowid, attribute, value) values('group1','test2','att1','val5');
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insert into ct(rowclass, rowid, attribute, value) values('group1','test2','att2','val6');
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insert into ct(rowclass, rowid, attribute, value) values('group1','test2','att3','val7');
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insert into ct(rowclass, rowid, attribute, value) values('group1','test2','att4','val8');
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SELECT *
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FROM crosstab(
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'select rowid, attribute, value
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from ct
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where rowclass = ''group1''
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and (attribute = ''att2'' or attribute = ''att3'') order by 1,2;', 3)
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AS ct(row_name text, category_1 text, category_2 text, category_3 text);
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row_name | category_1 | category_2 | category_3
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----------+------------+------------+------------
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test1 | val2 | val3 |
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test2 | val6 | val7 |
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(2 rows)
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==================================================================
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-- Joe Conway
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‎contrib/tablefunc/tablefunc-test.sql

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@@ -44,4 +44,6 @@ select * from crosstab2('select rowid, attribute, value from ct where rowclass =
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select * from crosstab3('select rowid, attribute, value from ct where rowclass = ''group2'' order by 1,2;');
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select * from crosstab4('select rowid, attribute, value from ct where rowclass = ''group2'' order by 1,2;');
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select * from crosstab('select rowid, attribute, value from ct where rowclass = ''group1'' order by 1,2;', 2) as c(rowid text, att1 text, att2 text);
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select * from crosstab('select rowid, attribute, value from ct where rowclass = ''group1'' order by 1,2;', 3) as c(rowid text, att1 text, att2 text, att3 text);
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select * from crosstab('select rowid, attribute, value from ct where rowclass = ''group1'' order by 1,2;', 4) as c(rowid text, att1 text, att2 text, att3 text, att4 text);

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