fix(bigquery): transpile DayOfWeek to EXTRACT(DAYOFWEEK FROM ...) - #8772

Fixes #8767

Transpiling DAYOFWEEK from MySQL, Spark, DuckDB or Snowflake to BigQuery previously produced DAY_OF_WEEK(...), which BigQuery does not have.

MySQL DAYOFWEEK, Spark dayofweek, and BigQuery EXTRACT(DAYOFWEEK FROM ...) all represent day-of-week with Sunday=1 to Saturday=7 semantics. This adds exp.DayOfWeek: _extract_part("DAYOFWEEK") to BigQueryGenerator.TRANSFORMS alongside the existing DayOfMonth, DayOfYear, and WeekOfYear mappings.

Example

import sqlglot

sqlglot.transpile("SELECT DAYOFWEEK(d)", read="mysql", write="bigquery")
# ['SELECT EXTRACT(DAYOFWEEK FROM CAST(d AS DATE))']

sqlglot.transpile("SELECT DAYOFWEEK(d)", read="spark", write="bigquery")
# ['SELECT EXTRACT(DAYOFWEEK FROM CAST(d AS DATE))']

sqlglot.transpile("SELECT DAYOFWEEK(d)", read="duckdb", write="bigquery")
# ['SELECT EXTRACT(DAYOFWEEK FROM d)']