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Aggregate small number of text items in overviews

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Instead of nulling text fields for non-singleton aggregated records
concatenate distinct text values when they're few (5 or less).
Fixes #231
This commit is contained in:
Javier Goizueta
2016-04-15 12:37:16 +02:00
parent 20989e2f28
commit 45f063d469
2 changed files with 29 additions and 12 deletions
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37
scripts-available/CDB_Overviews.sql
View File

@@ -515,6 +515,23 @@ BEGIN
END
$$ LANGUAGE PLPGSQL STABLE;
-- Check if a column of a table is of an unlimited-length text type
CREATE OR REPLACE FUNCTION _cdb_unlimited_text_column(reloid REGCLASS, col_name TEXT)
RETURNS BOOLEAN
AS $$
SELECT EXISTS (
SELECT *
FROM information_schema.columns c, pg_class _tn, pg_namespace _sn
WHERE table_name = _tn.relname
AND table_schema = _sn.nspname
AND c.column_name = col_name
AND _tn.oid = reloid
AND _sn.oid = _tn.relnamespace
AND character_maximum_length IS NULL
AND c.data_type IN ('text', 'character varying', 'character')
);
$$ LANGUAGE SQL STABLE;
-- SQL Aggregation expression for a datase attribute
-- Scope: private.
-- Parameters
@@ -532,6 +549,7 @@ DECLARE
has_counter_column BOOLEAN;
feature_count TEXT;
total_feature_count TEXT;
unlimited_text BOOLEAN;
BEGIN
IF table_alias <> '' THEN
qualified_column := Format('%I.%I', table_alias, column_name);
@@ -559,16 +577,15 @@ BEGIN
ELSE
RETURN Format('SUM(%s*%s)/%s::' || column_type, qualified_column, feature_count, total_feature_count);
END IF;
WHEN 'text' THEN
-- TODO: we could define a new aggregate function that returns distinct
-- separated values with a limit, adding ellipsis if more values existed
-- e.g. with '/' as separator and a limit of three:
-- 'A', 'B', 'A', 'C', 'D' => 'A/B/C/...'
-- Other ideas: if value is unique then use it, otherwise use something
-- like '*' or '(varies)' or '(multiple values)', or NULL
-- Using 'string_agg(' || qualified_column || ',''/'')'
-- here causes
RETURN 'CASE count(*) WHEN 1 THEN MIN(' || qualified_column || ') ELSE NULL END::' || column_type;
WHEN 'text', 'character varying', 'character' THEN
SELECT _cdb_unlimited_text_column(reloid, column_name) INTO unlimited_text;
IF unlimited_text THEN
-- TODO: this should not be applied to columns containing largish text;
-- it is intended only to short names/identifiers
RETURN 'CASE WHEN count(*) = 1 THEN MIN(' || qualified_column || ') WHEN ' || total_feature_count || ' < 5 THEN string_agg(distinct ' || qualified_column || ','' / '') ELSE ''*'' END::' || column_type;
ELSE
RETURN 'CASE count(*) WHEN 1 THEN MIN(' || qualified_column || ') ELSE NULL END::' || column_type;
END IF;
WHEN 'boolean' THEN
RETURN 'CASE count(*) WHEN 1 THEN BOOL_AND(' || qualified_column || ') ELSE NULL END::' || column_type;
ELSE

4
test/CDB_OverviewsTest_expect
View File

@@ -12,8 +12,8 @@ SELECT 1114
{_vovw_2_base_bare_t,_vovw_1_base_bare_t,_vovw_0_base_bare_t}
126
number,int_number,name,start
SUM(number*1)/count(*)::double precision AS number,SUM(int_number*1)/count(*)::integer AS int_number,CASE count(*) WHEN 1 THEN MIN(name) ELSE NULL END::text AS name,CASE count(*) WHEN 1 THEN MIN(start) ELSE NULL END::date AS start
SUM(tab.number*1)/count(*)::double precision AS number,SUM(tab.int_number*1)/count(*)::integer AS int_number,CASE count(*) WHEN 1 THEN MIN(tab.name) ELSE NULL END::text AS name,CASE count(*) WHEN 1 THEN MIN(tab.start) ELSE NULL END::date AS start
SUM(number*1)/count(*)::double precision AS number,SUM(int_number*1)/count(*)::integer AS int_number,CASE WHEN count(*) = 1 THEN MIN(name) WHEN count(*) < 5 THEN string_agg(distinct name,' / ') ELSE '*' END::text AS name,CASE count(*) WHEN 1 THEN MIN(start) ELSE NULL END::date AS start
SUM(tab.number*1)/count(*)::double precision AS number,SUM(tab.int_number*1)/count(*)::integer AS int_number,CASE WHEN count(*) = 1 THEN MIN(tab.name) WHEN count(*) < 5 THEN string_agg(distinct tab.name,' / ') ELSE '*' END::text AS name,CASE count(*) WHEN 1 THEN MIN(tab.start) ELSE NULL END::date AS start
{_vovw_2_base_t,_vovw_1_base_t,_vovw_0_base_t}
126