Function insert_returning 

pub async fn insert_returning(
    pool: &PgPool,
    query: &InsertQuery,
) -> Result<PgRow, ExecError>

Run an InsertQuery and return the row created by the RETURNING clause.

Used by macro-generated insert paths for models with Auto<T> PKs: the column is omitted from the INSERT (so Postgres’ BIGSERIAL sequence fires) and the assigned value is read back via RETURNING. Caller pulls each returned column out via sqlx::Row::try_get — e.g. Auto<i64>::decode rebuilds an Auto::Set(value).

Errors

Returns ExecError::EmptyReturning if query.returning is empty (use insert for those); validation, SQL-writing, or driver failures otherwise.