fix(community): postgres indexes getTime returning NaN due to missing alias

[jeremylevy]

Hello,

When running the SQL query included in the getTime() function on PostgreSQL 13.18, I got the following result:

date_part
1755534822.917985

This causes the function to return NaN since the extract property does not exist.

When the getTime function returns NaN, both the incremental and full cleanup operations remove all added documents, rendering the indexing feature unusable:

{ numAdded: 1, numDeleted: 1, numUpdated: 0, numSkipped: 0 }

This PR fixes the issue by always adding an alias using the AS SQL keyword.

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[hntrl]

@jeremylevy thanks for the PR!

Is this a regression between postgres versions? (i.e. was there once an additional extract property that came back from that query?) If so I think we'd want to have guards that cover both cases.

[jeremylevy]

Hey @hntrl,

The query always returns only one property, but it was rewritten to date_part in older versions of PostgreSQL. See, for example:
https://stackoverflow.com/questions/38442340/difference-between-extractyear-from-timestamp-function-and-date-partyear-t

This behavior changed in PostgreSQL 14: http://postgresql.org/docs/release/14.0/

Change EXTRACT() to return type numeric instead of float8 (Peter Eisentraut)
This avoids loss-of-precision issues in some usages. The old behavior can still be obtained by using the old underlying function date_part().
Also, EXTRACT(date) now throws an error for units that are not part of the date data type.

When running the same query on PostgreSQL 14, it returns the expected extract property name:

      extract      
-------------------
 1755551254.164705
(1 row)

Adding an alias does not change this behavior:

SELECT EXTRACT(EPOCH FROM CURRENT_TIMESTAMP) AS extract;

      extract      
-------------------
 1755551254.164705
(1 row)