基于函数的索引无法提高查询性能

Question

我已经创建了视图，并且在该视图中我添加了以下case语句，这是我需要的，并且我已经为此完全创建了基于函数的索引。该视图有1900000条记录。当我尝试执行视图时，需要花费数小时才能运行，并且该视图的性能非常低。我不明白如何提高性能。

CREATE OR REPLACE VIEW
    TST_AGG
    (
    ROOT) AS
    Select
     CASE
                WHEN regexp_like(ticker, '\s.*\s')
                THEN SUBSTR(ticker, 1, instr(ticker, ' ')-1)
                WHEN regexp_like(ticker, '\s')
                THEN
                    CASE
                        WHEN regexp_like(SUBSTR(ticker, 1, instr(ticker, ' ')-1), '(P|C)$')
                        AND LENGTH(SUBSTR(ticker, 1, instr(ticker, ' ')-1)) >= 4
                        THEN SUBSTR(SUBSTR(ticker, 1, instr(ticker, ' ')-1), 1, LENGTH(SUBSTR(ticker, 1
                            , instr(ticker, ' ')-1))-3)
                        WHEN regexp_like(SUBSTR(ticker, 1, instr(ticker, ' ')-1), '\w\d\d\w\d$')
                        THEN SUBSTR(SUBSTR(ticker, 1, instr(ticker, ' ')-1), 1, LENGTH(SUBSTR(ticker, 1
                            , instr(ticker, ' ')-1))-5)
                        WHEN regexp_like(SUBSTR(ticker, 1, instr(ticker, ' ')), '\w\d\w\d$')
                        THEN SUBSTR(SUBSTR(ticker, 1, instr(ticker, ' ')-1), 1, LENGTH(SUBSTR(ticker, 1
                            , instr(ticker, ' ')-1))-4)
                        ELSE SUBSTR(ticker, 1, instr(ticker, ' ')-1)
                    END
                WHEN regexp_like(ticker, '(P|C)$')
                AND LENGTH(ticker) >= 4
                THEN SUBSTR(ticker, 1, LENGTH(ticker)-3)
                WHEN regexp_like(ticker, '\w\d\d\w\d$')
                THEN SUBSTR(ticker, 1, LENGTH(ticker)-5)
                WHEN regexp_like(ticker, '\w\d\w\d$')
                THEN SUBSTR(ticker, 1, LENGTH(ticker)-4)
                ELSE ticker
            END ) AS ROOT
FROM TTT_IMP

下面是我创建的基于功能的索引：

CREATE INDEX "IDX_ROOT" ON "RRR_IMP" (CASE  WHEN  REGEXP_LIKE ("TICKER",'\s.*\s') THEN SUBSTR("TICKER",1,INSTR("TICKER",' ')-1) WHEN  REGEXP_LIKE ("TICKER",'\s') THEN CASE  WHEN ( REGEXP_LIKE (SUBSTR("TICKER",1,INSTR("TICKER",' ')-1),'(P|C)$') AND LENGTH(SUBSTR("TICKER",1,INSTR("TICKER",' ')-1))>=4) THEN SUBSTR(SUBSTR("TICKER",1,INSTR("TICKER",' ')-1),1,LENGTH(SUBSTR("TICKER",1,INSTR("TICKER",' ')-1))-3) WHEN  REGEXP_LIKE (SUBSTR("TICKER",1,INSTR("TICKER",' ')-1),'\w\d\d\w\d$') THEN SUBSTR(SUBSTR("TICKER",1,INSTR("TICKER",' ')-1),1,LENGTH(SUBSTR("TICKER",1,INSTR("TICKER",' ')-1))-5) WHEN  REGEXP_LIKE (SUBSTR("TICKER",1,INSTR("TICKER",' ')),'\w\d\w\d$') THEN SUBSTR(SUBSTR("TICKER",1,INSTR("TICKER",' ')-1),1,LENGTH(SUBSTR("TICKER",1,INSTR("TICKER",' ')-1))-4) ELSE SUBSTR("TICKER",1,INSTR("TICKER",' ')-1) END  WHEN ( REGEXP_LIKE ("TICKER",'(P|C)$') AND LENGTH("TICKER")>=4) THEN SUBSTR("TICKER",1,LENGTH("TICKER")-3) WHEN  REGEXP_LIKE ("TICKER",'\w\d\d\w\d$') THEN SUBSTR("TICKER",1,LENGTH("TICKER")-5) WHEN  REGEXP_LIKE ("TICKER",'\w\d\w\d$') THEN SUBSTR("TICKER",1,LENGTH("TICKER")-4) ELSE "TICKER" END );

Answer 1

索引可以在两种情况下使用。

1）减少选择的记录，即

SELECT ... FROM TST_AGG where ROOT = ...

2）为避免查询表，并避免进行昂贵的计算

SELECT ROOT FROM TST_AGG

我在这里假设后者。如果优化器知道索引条目与表是一对一的，则只能使用索引（代替表）。因为它不知道该表达式是否可以返回NULL（未存储在索引中），所以除非您通知优化器，否则它无法进行直接交换。

因此

SELECT ROOT FROM TST_AGG

将没有机会使用索引，但是

SELECT ROOT FROM TST_AGG WHERE ROOT IS NOT NULL

应该能够。

要注意的另一件事是，我们可能会更改用于存储索引的表达式语法。因此，请检查USER_IND_EXPRESSIONS，然后也许将该表达式放回视图的定义中。

Answer 2

我建议检查一下您的数据模型，正则表达式确实很丑陋。将相关信息直接存储在列中，而不要存储在ticket字符串中隐藏的位置。

无论如何，我建议创建一个虚拟列而不是视图。然后，您可以在此虚拟列上创建索引，并且也应该使用它。类似于以下内容：

ALTER TABLE TTT_IMP ADD (ROOT VARCHAR2(20) GENERATED ALWAYS AS (
CAST(
    CASE
    WHEN regexp_like(ticker, '\s.*\s')
    THEN SUBSTR(ticker, 1, instr(ticker, ' ')-1)
    WHEN regexp_like(ticker, '\s')
    THEN
        CASE
            WHEN regexp_like(SUBSTR(ticker, 1, instr(ticker, ' ')-1), '(P|C)$')
            AND LENGTH(SUBSTR(ticker, 1, instr(ticker, ' ')-1)) >= 4
            THEN SUBSTR(SUBSTR(ticker, 1, instr(ticker, ' ')-1), 1, LENGTH(SUBSTR(ticker, 1
                , instr(ticker, ' ')-1))-3)
            WHEN regexp_like(SUBSTR(ticker, 1, instr(ticker, ' ')-1), '\w\d\d\w\d$')
            THEN SUBSTR(SUBSTR(ticker, 1, instr(ticker, ' ')-1), 1, LENGTH(SUBSTR(ticker, 1
                , instr(ticker, ' ')-1))-5)
            WHEN regexp_like(SUBSTR(ticker, 1, instr(ticker, ' ')), '\w\d\w\d$')
            THEN SUBSTR(SUBSTR(ticker, 1, instr(ticker, ' ')-1), 1, LENGTH(SUBSTR(ticker, 1
                , instr(ticker, ' ')-1))-4)
            ELSE SUBSTR(ticker, 1, instr(ticker, ' ')-1)
        END
    WHEN regexp_like(ticker, '(P|C)$')
    AND LENGTH(ticker) >= 4
    THEN SUBSTR(ticker, 1, LENGTH(ticker)-3)
    WHEN regexp_like(ticker, '\w\d\d\w\d$')
    THEN SUBSTR(ticker, 1, LENGTH(ticker)-5)
    WHEN regexp_like(ticker, '\w\d\w\d$')
    THEN SUBSTR(ticker, 1, LENGTH(ticker)-4)
    ELSE ticker
    END
AS VARCHAR2(20))
) VIRTUAL);