Doc: add a bit to indices.sgml about what is an indexable clause.
We didn't explain this clearly until somewhere deep in the
"Extending SQL" chapter, but really it ought to be mentioned
in the introductory material too.
Discussion: https://postgr.es/m/4097442.1694967650@sss.pgh.pa.us
Branch
------
REL_15_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/afc987e196107b0887314838256a885af05b8714
Modified Files
--------------
doc/src/sgml/indices.sgml | 35 ++++++++++++++++++++++++++++++++++-
1 file changed, 34 insertions(+), 1 deletion(-)