fix(duckdb): add ParseDatetime transpilation for BigQuery to DuckDB

[william-goode]

Summary

BigQuery's PARSE_DATETIME is parsed into exp.ParseDatetime but DuckDB's generator has no handler. Falls through to function_fallback_sql and emits PARSE_DATETIME(...) verbatim — DuckDB rejects this.

Fix: Add parsedatetime_sql to DuckDBGenerator mapping to STRPTIME. No CAST needed (unlike ParseTime/StrToDate) since STRPTIME already returns TIMESTAMP. No TRY_STRPTIME conditional since ParseDatetime has no safe arg.

Reproduction

import sqlglot

# Before: falls through
sqlglot.transpile("SELECT PARSE_DATETIME('%Y-%m-%d %H:%M:%S', '2023-01-15 14:30:00')", read="bigquery", write="duckdb")
# => ["SELECT PARSE_DATETIME('2023-01-15 14:30:00', '%Y-%m-%d %H:%M:%S')"]

# After
# => ["SELECT STRPTIME('2023-01-15 14:30:00', '%Y-%m-%d %H:%M:%S')"]

Test plan

• Three validate_all tests: standard datetime format, named day/month with 12-hour clock, microsecond precision (%E6S)
• make unit: 1219 passed, 0 failures
• BigQuery and DuckDB dialect tests green

[geooo109]

@william-goode let's move on with the concatenation for the solution.

So let's do the following:

1. Add a new flag on the AST node and populate it from the bigquery side (parsing) with the default year 1970
2. On the duckdb side (generation) apply the concatenation, it should look like this: (you should apply this only if the default year is populated, otherwise we should follow the default roundtrip that we already have)

STRPTIME('1970 ' <- this is set by the bq parser || <value>, '%Y ' || <format>)

[georgesittas]

Hey @william-goode, any plans to take this to the finish line?

[william-goode]

@georgesittas Yes! Sorry, got caught up with work.

@geooo109 Yes chef.

Thanks for the feedback fellas - changes coming shortly.

[georgesittas]

Cool, no worries & thanks for following up!

[william-goode]

Patched with concatenation approach and ready for review.

A knock-on effect:

The BigQuery parser sets default_year = True at build-time, but ClickHouse also lowers its PARSEDATETIME into an exp.ParseDatetime node. Previously, this would emit PARSE_DATETIME, which DuckDB rejects. So this should be a strict improvement over main. It now routes to the new DuckDB handler. The ClickHouse builder does not set default_year = True and the 1970 prepend is gated on this flag, so no 1970 is applied to ClickHouse nodes. If ClickHouse happens to also need a default year of 1970, that could be added. I'm not a regular user of ClickHouse so I'll refrain from guessing at the answer.