Overload CDB_Overviews to accept either a single table or an array

The result of CDB_Overviews has been expandend with a base_table column

doc/CDB_Overviews.md

@@ -53,16 +53,42 @@ CDB_CreateOverviews(table_name, ref_z_strategy, reduction_strategy)
 Obtain overview metadata for a given table (existing overviews).
 The returned relation will be empty if the table has no overviews.
 
+The function can be applied to a single table:
+
 ```sql
 SELECT CDB_Overviews('table_name');
 --- Return existing overview Z levels and corresponding tables
 ```
 
+Or to multiple tables passed as an array; this can be used
+to obtain the overviews that can be applied to a query by
+combining it with `CDB_QueryTablesText`:
+
+```sql
+SELECT CDB_Overviews(CDB_QueryTablesText('SELECT * FROM table1, table2'));
+--- Return existing overview Z levels and corresponding tables
+```
+
+The result of `CDB_Overviews` has three columns:
+
+| base_table | z | overview_table |
+|------------+---+----------------|
+| table1     | 1 | table1_ov1     |
+| table1     | 2 | table1_ov2     |
+| table1     | 4 | table1_ov4     |
+| table2     | 1 | table1_ov1     |
+| table2     | 2 | table1_ov2     |
+
 #### Arguments
 
 CDB_Overviews(table_name)
 
-* **table_name** regclass, table to obtain existing overviews for
+* **table_name** regclass, oid of table to obtain existing overviews for
+
+CDB_Overviews(table_names)
+
+* **table_names** regclass[], array of table oids
+
 
 ### CDB_DropOverviews
 

scripts-available/CDB_Overviews.sql

@@ -17,20 +17,24 @@ BEGIN
 END;
 $$ LANGUAGE PLPGSQL VOLATILE;
 
+
+
 -- Return existing overviews (if any) for a given dataset table
 -- Scope: public
 -- Parameters
 --   reloid: oid of the input table.
 -- Return relation of overviews for the table with
--- z level of the overview and overview table, ordered by z.
+-- the base table oid,
+-- z level of the overview and overview table oid, ordered by z.
 CREATE OR REPLACE FUNCTION CDB_Overviews(reloid REGCLASS)
-RETURNS TABLE(z integer, overview_table REGCLASS)
+RETURNS TABLE(base_table REGCLASS, z integer, overview_table REGCLASS)
 AS $$
   -- FIXME: this will fail if the overview tables
   -- require a explicit schema name
   -- possible solutions: return table names as text instead of regclass
   -- or add schema of reloid before casting to regclass
   SELECT
+    reloid as base_table,
     substring(cdb_usertables from '\d+$')::integer as z,
     cdb_usertables::regclass as overview_table
     FROM CDB_UserTables()
@@ -38,6 +42,27 @@ AS $$
     ORDER BY z;
 $$ LANGUAGE SQL;
 
+-- Return existing overviews (if any) for multiple dataset tables.
+-- Scope: public
+-- Parameters
+--   tables: Array of input tables oids
+-- Return relation of overviews for the table with
+-- the base table oid,
+-- z level of the overview and overview table oid, ordered by z.
+-- Note: CDB_Overviews can be applied to the result of CDB_QueryTablesText
+-- to obtain the overviews applicable to a query.
+CREATE OR REPLACE FUNCTION CDB_Overviews(tables regclass[])
+RETURNS TABLE(base_table REGCLASS, z integer, overview_table REGCLASS)
+AS $$
+  SELECT
+    base_table::regclass AS base_table, substring(cdb_usertables from '\d+$')::integer as z,
+    cdb_usertables::regclass as overview_table
+    FROM
+      CDB_UserTables(), unnest(tables) base_table
+    WHERE cdb_usertables SIMILAR TO (SELECT relname FROM pg_class WHERE oid=base_table) || '_ov[\d]+'
+    ORDER BY base_table, z;
+$$ LANGUAGE SQL;
+
 -- Schema and relation names of a table given its reloid
 -- Scope: private.
 -- Parameters

test/CDB_OverviewsTest.sql

@@ -18,6 +18,9 @@ SELECT _CDB_Aggregated_Attributes_Expression('base_t'::regclass, 'tab');
 SELECT CDB_CreateOverviews('base_t'::regclass);
 SELECT count(*) FROM base_t_ov5;
 
+SELECT CDB_Overviews('base_t'::regclass);
+SELECT CDB_Overviews(ARRAY['base_t'::regclass, 'base_bare_t'::regclass]);
+
 
 SELECT CDB_DropOverviews('base_bare_t'::regclass);
 SELECT CDB_DropOverviews('base_t'::regclass);

test/CDB_OverviewsTest_expect

@@ -13,6 +13,24 @@ AVG(number)::double precision AS number,AVG(int_number)::integer AS int_number,C
 AVG(tab.number)::double precision AS number,AVG(tab.int_number)::integer AS int_number,CASE count(*) WHEN 1 THEN string_agg(tab.name,'/') ELSE '*' END::text AS name,CASE count(*) WHEN 1 THEN MIN(tab.start) ELSE NULL END::date AS start
 {base_t_ov5,base_t_ov4,base_t_ov3,base_t_ov2,base_t_ov1,base_t_ov0}
 125
+(base_t,0,base_t_ov0)
+(base_t,1,base_t_ov1)
+(base_t,2,base_t_ov2)
+(base_t,3,base_t_ov3)
+(base_t,4,base_t_ov4)
+(base_t,5,base_t_ov5)
+(base_bare_t,0,base_bare_t_ov0)
+(base_bare_t,1,base_bare_t_ov1)
+(base_bare_t,2,base_bare_t_ov2)
+(base_bare_t,3,base_bare_t_ov3)
+(base_bare_t,4,base_bare_t_ov4)
+(base_bare_t,5,base_bare_t_ov5)
+(base_t,0,base_t_ov0)
+(base_t,1,base_t_ov1)
+(base_t,2,base_t_ov2)
+(base_t,3,base_t_ov3)
+(base_t,4,base_t_ov4)
+(base_t,5,base_t_ov5)
 
 
 ERROR:  relation "base_t_ov5" does not exist