以Debug Friendly方式重写/重新格式化多个嵌套子查询

Question

是否有更好的方法来重写多个嵌套的子查询，以便更容易理解和调试，而不会影响性能？

（注意：在我的情况下，我得到了一堆相当复杂的子查询，许多具有多个连接，where子句和一些得到case语句等。将所有内容编写为一大块代码是一个调试噩梦）

例如：我想重写一下：

SELECT DoSomething(x) AS x
FROM (SELECT DoSomething(x) AS x
      FROM (SELECT DoSomething(x) AS x
            FROM (SELECT DoSomething(x) AS x
                  FROM (SELECT DoSomething(x) AS x
                        FROM (SELECT x
                              FROM tbl_1) AS Q1) AS Q2) AS Q3) AS Q4) AS Q5

进入这样的事情：

--Q1
SELECT *
INTO #Q1
FROM (SELECT x
      FROM tbl_1) AS Q1

--Q2
SELECT *
INTO #Q2
FROM (SELECT DoSomething(x)
      FROM Q1) AS Q2

--Q3
SELECT *
INTO #Q3
FROM (SELECT DoSomething(x)
      FROM Q2) AS Q3

--Q4
SELECT *
INTO #Q4
FROM (SELECT DoSomething(x)
      FROM Q3) AS Q3

--Q5
SELECT *
INTO #Q5
FROM (SELECT DoSomething(x)
      FROM Q4) AS Q4

--Do Something with Q5 then cleanup

DROP TABLE #Q1
DROP TABLE #Q2
DROP TABLE #Q3
DROP TABLE #Q4
DROP TABLE #Q5

上面的例子虽然更多代码（希望）允许调试器更容易地查看/选择单个子查询并帮助他/她缩小潜在问题

Answer 1

你可能想看看CTEs。

你可以写下你的例子：

WITH
Q1
AS
(
SELECT x
       FROM tbl_1
),
Q2
AS
SELECT DoSomething(x)
       FROM Q1
),
Q3
AS
(
SELECT DoSomething(x)
       FROM Q2
),
Q4
AS
(
SELECT DoSomething(x)
       FROM Q3
),
Q5
AS
(
SELECT DoSomething(x)
       FROM Q4
)
SELECT *
       FROM Q5;