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当Oracle日期类型为varchar2时，通过oracle_fdw在PostgreSQL中执行查询时，使用比较运算符>=进行查询，这种情况下不能使用索引。

不能使用索引：

>= to_char(now() - interval '7' day, 'YYYYMMDD')

Output: a.date, a.cusno
Filter: ((a.date)::date >= ((now() - '07 days'::interval day))::date)
                    Oracle query: SELECT /*a05802d21e2d4cec93da21f1abf9ffbb*/ r1."DATE", r1."CUSNO" FROM "ORACLEDB"."CXXXINFO" r1 WHERE (r1."CUSNO" = '12345')
                    Oracle plan: SELECT STATEMENT
                    Oracle plan:   TABLE ACCESS FULL CXXXINFO  (filter "R1"."CUSNO"='12345')

但是 = 在这种情况下，使用索引。

使用索引：

= to_char(now() - interval '7' day, 'YYYYMMDD')

Output: a.date, a.cusno
Oracle query: SELECT /*b7552642e64dd971ba5293a42d581661*/ r1."DATE", r1."CUSNO"
WHERE (r1."CUSNO" = '12345') AND (r1."DATE" = to_char(((CAST (:now AS
TIMESTAMP WITH TIME ZONE)) - INTERVAL '07 00:00:00.000000' DAY(9) TO
SECOND(6)), 'YYYYMMDD'))
Oracle plan: SELECT STATEMENT
Oracle plan:   TABLE ACCESS BY INDEX ROWID CXXXINFO
Oracle plan:     INDEX SKIP SCAN CXXXINFO_01 (condition "R1"."CUSNO"='12345' AND "R1"."DATE"=TO_CHAR(CAST(:NOW AS
TIMESTAMP WITH TIME ZONE)-INTERVAL'+000000007 00:00:00.000000' DAY(9)
TO SECOND(6),'YYYYMMDD'))(filter "R1"."DATE"=TO_CHAR(CAST(:NOW AS TIMESTAMP WITH TIME > ZONE)-INTERVAL'+000000007 00:00:00.000000' DAY(9) TO
> SECOND(6),'YYYYMMDD'))

我可以知道有什么区别吗？

我目前使用的是 Oracle 19.0.2 版本

PostgreSQl oracle_fdw 2.2

和 PostgreSQL 12.7

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1 回答 1

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The problem is that you store your dates as strings.

oracle_fdw will push down = and <> comparisons, but not <, <=, > and >=. This is because such comparisons depend on the collation, and collations can be different in Oracle and PostgreSQL, even if they are both English. That could mean that the query result might be different, depending on whether <= is pushed down or not, which is not acceptable.

Use DATE instead of VARCHAR2. Perhaps you can create an Oracle view that converts the string to a DATE.

于 2021-08-20T04:48:06.220 回答