在子查询中使用空的 OVER() 子句

Question

我有一个使用相关子查询的 Oracle SQL 查询：

Q1 P>

SELECT t1.id,
       t3.code,
       t3.processed_date,
       (t1.total / t2.rate) 
FROM table1 t1
         JOIN table2 t2 ON t2.code= t1.code
         JOIN table3 t3 ON t3.id = t1.id
         JOIN table4 t4 ON t4.code = t1.code
    AND t4.type IN ('value1', 'value2', 'value3')
    AND t3.processed_date >= '01 JUL 2019'
    AND t3.processed_date < '22 JUL 2019'
    AND t2.effective_date IN (SELECT max(tc.effective_date)
                                FROM tableCore tc
                                WHERE tc.effective_date <= t3.processed_date
                                  AND t1.code = tc.code)

我已将子查询更改为 Empty OVER() 原因，这显着提高了此查询的性能：

Q2 P>

SELECT t1.id,
       t3.code,
       t3.processed_date,
       (t1.total / t2.rate) 
FROM table1 t1
         JOIN table2 t2 ON t2.code= t1.code
         JOIN table3 t3 ON t3.id = t1.id
         JOIN table4 t4 ON t4.code = t1.code
    AND t4.type IN ('value1', 'value2', 'value3')
    AND t3.processed_date >= '01 JUL 2019'
    AND t3.processed_date < '22 JUL 2019'
    AND t2.effective_date IN (SELECT max(tc.effective_date) OVER () AS ed
                                FROM tableCore tc
                                WHERE tc.effective_date <= t3.processed_date
                                  AND t1.code = tc.code)

新查询返回与原始查询相同的结果集，因此似乎正在运行...，但是为什么解释计划如此不同，它似乎仍然相关，它不是对外部查询了吗？为什么？

我想了解第二个查询中发生了什么。

我想我可以使用row_number() OVER (partition by ...) 以第三种方式重写此查询：

Q3 P>

    SELECT t1.id,
       t3.code,
       t3.processed_date,
       (t1.total / t2.rate),
       ct.*
FROM table1 t1
         JOIN table2 t2 ON t2.code = t1.code
         JOIN table3 t3 ON t3.id = t1.id
         JOIN table4 t4 ON t4.code = t1.code
         JOIN (SELECT ct.*, row_number() OVER (PARTITION BY ct.code ORDER BY ct.effective_date ASC) AS rn
               FROM tablecore ct) ct
              ON t1.code = ct.code
                  AND rn = 1
                  AND ct.effective_date <= t3.processed_date
WHERE t2.effective_date in(ct.effective_date)
  AND t4.type IN ('value1', 'value2', 'value3')
  AND t3.processed_date >= '01 JUL 2019'
  AND t3.processed_date < '22 JUL 2019'
  AND t2.effective_date IN (ct.effective_date);

这个版本似乎也可以，但是比第二个版本慢。

编辑 正如@Christian Q3 指出的那样，将返回不正确的结果

Answer 1

这里有另一个选项供您尝试：

SELECT t1.id,
       t3.code,
       t3.processed_date,
       (t1.total / t2.rate) 
FROM table1 t1
         JOIN table2 t2 ON t2.code= t1.code
         JOIN table3 t3 ON t3.id = t1.id
         JOIN table4 t4 ON t4.code = t1.code
    AND t4.type IN ('value1', 'value2', 'value3')
    AND t3.processed_date >= '01 JUL 2019'
    AND t3.processed_date < '22 JUL 2019'
    AND EXISTS (SELECT 1
                                FROM tableCore tc
                                WHERE tc.effective_date <= t3.processed_date
                                  AND t1.code = tc.code
                                HAVING t2.effective_date = max(tc.effective_date))

对于正确的性能分析，最好有表的大小，以及不同查询的解释计划（如果优化器统计信息准确，还需要检查）。

仅供参考：您使用 row_number() 进行的最后一次查询将不会提供相同的结果，因为将在连接 ct.effective_date <= t3.processed_date 之前评估窗口函数，因此您会错过一些行。

Answer 2

当您可以简单地使用= 运算符时，您为什么还要使用IN

SELECT t1.id,
       t3.code,
       t3.processed_date,
       (t1.total / t2.rate) 
FROM table1 t1
         JOIN table2 t2 ON t2.code= t1.code
         JOIN table3 t3 ON t3.id = t1.id
         JOIN table4 t4 ON t4.code = t1.code
    AND t4.type IN ('value1', 'value2', 'value3')
    AND t3.processed_date >= '01 JUL 2019'
    AND t3.processed_date < '22 JUL 2019'
    AND t2.effective_date = (SELECT max(tc.effective_date)
                                FROM tableCore tc
                                WHERE tc.effective_date <= t3.processed_date
                                  AND t1.code = tc.code)

显着的性能提升是因为磁盘 I/O 减少