Metabase: support information_schema._pg_expandarray

[neverchanje]

    SELECT 
      NULL AS TABLE_CAT, 
      n.nspname AS TABLE_SCHEM, 
      ct.relname AS TABLE_NAME, 
      a.attname AS COLUMN_NAME, 
      (
        information_schema._pg_expandarray(i.indkey)
      ).n AS KEY_SEQ, 
      ci.relname AS PK_NAME, 
      information_schema._pg_expandarray(i.indkey) AS KEYS, 
      a.attnum AS A_ATTNUM 
    FROM 
      pg_catalog.pg_class ct 
      JOIN pg_catalog.pg_attribute a ON (ct.oid = a.attrelid) 
      JOIN pg_catalog.pg_namespace n ON (ct.relnamespace = n.oid) 
      JOIN pg_catalog.pg_index i ON (a.attrelid = i.indrelid) 
      JOIN pg_catalog.pg_class ci ON (ci.oid = i.indexrelid) 
    WHERE 
      true 
      AND n.nspname = 'public' 
      AND ct.relname = 'sentences' 
      AND i.indisprimary

I have ensured that all features have been supported except _pg_expandarray. Popular PG-compatible databases all have supported it. This is the main blocker for Metabase to load RW schemas.

[xxchan]

The definition in PG is
https://github.com/postgres/postgres/blob/e0b2eed047df9045664da6f724cb42c10f8b12f0/src/backend/catalog/information_schema.sql#L42C1-L50

/* Expand any 1-D array into a set with integers 1..N */
CREATE FUNCTION _pg_expandarray(IN anyarray, OUT x anyelement, OUT n int)
    RETURNS SETOF RECORD
    LANGUAGE sql STRICT IMMUTABLE PARALLEL SAFE
    AS 'select $1[s],
        s operator(pg_catalog.-) pg_catalog.array_lower($1,1) operator(pg_catalog.+) 1
        from pg_catalog.generate_series(pg_catalog.array_lower($1,1),
                                        pg_catalog.array_upper($1,1),
                                        1) as g(s)';