Both Postgres & SQL Server support EXPLAIN on DML without running the statement (with varying levels of depth).

    CREATE TEMPORARY TABLE tmp_blah (num INT);
    EXPLAIN INSERT INTO tmp_blah SELECT * FROM generate_series(1, 100000) ORDER BY random();

    QUERY PLAN
    Insert on tmp_blah  (cost=62.33..74.83 rows=1000 width=4)
        ->  Subquery Scan on "*SELECT*"  (cost=62.33..74.83 rows=1000 width=4)
            ->  Sort  (cost=62.33..64.83 rows=1000 width=12)
                Sort Key: (random())
                ->  Function Scan on generate_series  (cost=0.00..12.50 rows=1000 width=12)