Adding an index to a table in Hibernate issues a query which makes use of this. Note that supporting this also means that we would need to support record types. The query below should work, if this is implemented:

SELECT (i.keys).n FROM (SELECT information_schema._pg_expandarray(indkey) AS keys FROM pg_index) AS i;

This function takes an array a and returns a set of records that looks like the following:

 x   |  n
----------
a[1] |  1
a[2] |  2
a[3] |  3
a[4] |  4
...

The work is to be decomposed as follows:

• support the set-generating function information_schema._pg_expandarray sql: Add the builtin function _pg_expandarray() #24422
• support simple labeled tuple access
  • add tuple labels sql: add labels to Tuples #25283
  • access different columns in SRF sql: add the ability to access a column from the results of an SRF #24832
• support in-flight composite types sql: support lightweight composite types for in-flight values #24866.
  • propagate labels during typing, including subqueries sql,opt: propagate composite types (labeled tuples) #26621
  • labeled tuple serialization bug sql: tuples not properly preserved during serialization #26624.
  • labeled tuples in distsql sql: distsql does not support labeled tuples #26627.
• verify that all the complex queries listed here and in the srfs logic test file work properly
  • add pg_get_indexdef with 3 arguments sql: support pg_get_indexdef with 3 arguments #26629
  • fix the column pg_index.indclass sql: fix the column pg_index.indclass #26504