Support postgres omitted interval span unit

[treysp]

This PR adds support for handling postgres INTERVAL literal spans that omit the span units, both parsing and inferring the correct units for transpilation.

Examples

• INTERVAL '1 00:01'
• INTERVAL '1 00:01:01'

Context: INTERVALs

interval literals generally consist of the word INTERVAL , a string literal like '6' and a unit string like DAYS

• Example: INTERVAL '6' DAYS

in many dialects you may specify compound units, which we parse into exp.IntervalSpan based on the presence of "TO"

• Example: INTERVAL '163 12:39' DAY TO MINUTE
• Example: INTERVAL '163 12:39:59.1' DAY TO SECOND

Context: postgres

Postgres lets you omit the unit strings DAY TO MINUTE and DAY TO SECOND if the second element in the literal is a hh:[mm:[ss[.ff]]]

• Valid examples confirmed to work in postgres 14:
  • INTERVAL '1 01:01:01.01'
  • INTERVAL '1 01:01:01'
  • INTERVAL '1 01:01'
  • INTERVAL '1.5 01:'
  • INTERVAL '-0.25 01:'
• Invalid example
  • No colon present: INTERVAL '1 01'

This issue

If the span unit is omitted, we incorrectly ingest the token following the literal because we assume it's a unit like DAY

• Example: a > INTERVAL '1 00:00' AND TRUE
  • We consume AND so don't recognize the compound condition