lightdb使用一条sql实现高性能事务一致性归历史

相比insert select，delete，如下：

-- lightdb专有oracle匿名块写法
BEGIN TRANSACTION ISOLATION LEVEL REPEATABLE READ;
insert into xx select xx from yy where id < xxx;
delete form yy where id < xxx;
end;
/

使用with delete insert实现数据移动，不仅性能更加、也能保持一致性，如下：

explain
WITH moved_rows AS (
    delete from lem_db_log_102200 ldl where id < 119894653
    RETURNING *
)
INSERT INTO lem_db_log_new_102232
SELECT * FROM moved_rows;

由于postgresql不支持delete limit，所以通常需要依赖where id限制，在lightdb中，则可以直接where limit，如下：

WITH moved_rows AS (
    delete from lem_db_log_102200 ldl limit 100
    RETURNING *
)
INSERT INTO lem_db_log_new_102232
SELECT * FROM moved_rows;