Function pushdown_cte_column_names 

pub fn pushdown_cte_column_names(expr: Expression) -> Result<Expression>

Push down CTE column names into SELECT expressions.

BigQuery doesn’t support column names when defining a CTE, e.g.: WITH vartab(v) AS (SELECT ...) is not valid. Instead, it expects: WITH vartab AS (SELECT ... AS v).

This transform removes the CTE column aliases and adds them as aliases on the SELECT expressions.