Port this query and tell me what shifts

Moving a query between Postgres, BigQuery, Snowflake, MySQL, or SQLite.

Convert this query to the target dialect. Give me a working version, then list what changed, grouped by syntax, date handling, and NULL semantics. Call out behaviour that differs even where the syntax converts cleanly: integer division, NULL ordering, DISTINCT with NULLs. Flag anything I must verify against real data.

Source dialect:
Target dialect:
Query:

Writing and reading queries. Drafting SQL from a plain question, making an inherited query legible, and moving it between dialects.