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Use mode to aggregate categorical columns in overviews

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Fixes #245
This commit is contained in:
Javier Goizueta
2016-04-26 15:15:24 +02:00
parent 1358964628
commit 9a73703954
1 changed files with 52 additions and 6 deletions
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58
scripts-available/CDB_Overviews.sql
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@@ -531,6 +531,44 @@ AS $$
);
$$ LANGUAGE SQL STABLE;
CREATE OR REPLACE FUNCTION _cdb_categorical_column(reloid REGCLASS, col_name TEXT)
RETURNS BOOLEAN
AS $$
DECLARE
schema_name TEXT;
table_name TEXT;
categorical BOOLEAN;
BEGIN
SELECT * FROM _cdb_split_table_name(reloid) INTO schema_name, table_name;
SELECT n_distinct IS NOT NULL AND n_distinct > 0 AND n_distinct <= 20
FROM pg_stats
WHERE pg_stats.schemaname = schema_name
AND pg_stats.tablename = table_name
AND pg_stats.attname = col_name
INTO categorical;
RETURN categorical;
END;
$$ LANGUAGE PLPGSQL STABLE;
CREATE OR REPLACE FUNCTION _cdb_mode_of_array(anyarray)
RETURNS anyelement AS
$$
SELECT a
FROM unnest($1) a
GROUP BY 1
ORDER BY COUNT(1) DESC, 1
LIMIT 1;
$$
LANGUAGE SQL IMMUTABLE;
-- Tell Postgres how to use our aggregate
CREATE AGGREGATE _cdb_mode(anyelement) (
SFUNC=array_append,
STYPE=anyarray,
FINALFUNC=_cdb_mode_of_array,
INITCOND='{}'
);
-- SQL Aggregation expression for a datase attribute
-- Scope: private.
-- Parameters
@@ -573,15 +611,23 @@ BEGIN
IF column_name = '_feature_count' THEN
RETURN 'SUM(_feature_count)';
ELSE
RETURN Format('SUM(%s*%s)/%s::' || column_type, qualified_column, feature_count, total_feature_count);
IF column_type = 'integer' AND _cdb_categorical_column(reloid, column_name) THEN
RETURN Format('CDB_Math_Mode(%s)::', qualified_column) || column_type;
ELSE
RETURN Format('SUM(%s*%s)/%s::' || column_type, qualified_column, feature_count, total_feature_count);
END IF;
END IF;
WHEN 'text', 'character varying', 'character' THEN
IF _cdb_unlimited_text_column(reloid, column_name) THEN
-- TODO: this should not be applied to columns containing largish text;
-- it is intended only to short names/identifiers
RETURN 'CASE WHEN count(distinct ' || qualified_column || ') = 1 THEN MIN(' || qualified_column || ') WHEN ' || total_feature_count || ' < 5 THEN string_agg(distinct ' || qualified_column || ','' / '') ELSE ''*'' END::' || column_type;
IF _cdb_categorical_column(reloid, column_name) THEN
RETURN Format('_cdb_mode(%s)::', qualified_column) || column_type;
ELSE
RETURN 'CASE count(*) WHEN 1 THEN MIN(' || qualified_column || ') ELSE NULL END::' || column_type;
IF _cdb_unlimited_text_column(reloid, column_name) THEN
-- TODO: this should not be applied to columns containing largish text;
-- it is intended only to short names/identifiers
RETURN 'CASE WHEN count(distinct ' || qualified_column || ') = 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;
END IF;
WHEN 'boolean' THEN
RETURN 'CASE count(*) WHEN 1 THEN BOOL_AND(' || qualified_column || ') ELSE NULL END::' || column_type;