同一查询中两次更新的意外结果

Question

    with
    u1 as (
        update todel set val=val+1 where id='key' returning *
    ),
    u2 as (
        update todel set val=val+2 where id='key' returning *
    )
    select * from u1
    union all
    select * from u2
    ;

预期结果是两行，但我得到了一行，

     id  | val
    -----+-----
     key |  11

为什么会这样，我错过了什么？服务器是 pg 9.6.6

Answer 1

每the documentation:

The sub-statements in WITH are executed concurrently with each other and with the main query. Therefore, when using data-modifying statements in WITH, the order in which the specified updates actually happen is unpredictable.

结果好像只执行了一个