cx_Oracle忽略order by子句

Question

我在我的项目中创建了复杂的查询构建器,并且在测试期间偶然发现了奇怪的问题:具有相同计划的相同查询在不同客户端上产生不同的结果:cx_Oracle忽略order by子句,而Oracle SQLDeveloper Studio正确处理查询,但在这两种情况下在两个计划中按目前排序.

有问题的查询是:

select *
from
(
    select 
        a.*,
        ROWNUM tmp__rnum
    from
    (
        select base.* 
        from
        (
            select id
            from
            (
                (
                    select 
                    profile_id as id,
                    surname as sort__col 
                    from names
                )
                /* here usually are several other subqueries chained by unions */
            )
            group by id
            order by min(sort__col) asc
        ) tmp
        left join (profiles) base
        on tmp.id = base.id
        where exists 
        (
            select t.object_id 
            from object_rights t 
            where
                    t.object_id = base.id 
                and t.subject_id = :a__subject_id 
                and t.rights in ('r','w') 
        )
    ) a 
    where ROWNUM < :rows_to 
) 
where tmp__rnum >= :rows_from

如果我错过了什么,请从cx_Oracle计划:

{'operation': 'SELECT STATEMENT', 'position': 9225, 'cardinality': 2164, 'time': 1, 'cost': 9225, 'depth': 0, 'bytes': 84396, 'optimizer': 'ALL_ROWS', 'id': 0, 'cpu_cost': 1983805801},

    {'operation': 'VIEW', 'position': 1, 'filter_predicates': '"TMP__RNUM">=TO_NUMBER(:ROWS_FROM)', 'parent_id': 0, 'object_instance': 1, 'cardinality': 2164SEL$1', 'projection': '"from$_subquery$_001"."ID"[NUMBER,22], "from$_subquery$_001"."CREATION_TIME"[TIMESTAMP,11], "TMP__RNUM"[NUMBER,22]', 'time': 1, 'cost': 9225, 'depth': 1, 'bytes': 84396, 'id': 1, 'cpu_cost': 1983805801},

        {'operation': 'COUNT', 'position': 1, 'filter_predicates': 'ROWNUM<TO_NUMBER(:ROWS_TO)', 'parent_id': 1, 'projection': '"BASE"."ID"[NUMBER,22], "BASE"."CREATION_TIME"[TIMESTAMP,11], ROWNUM[8]', 'options': 'STOPKEY', 'depth': 2, 'id': 2, 

            {'operation': 'HASH JOIN', 'position': 1, 'parent_id': 2, 'access_predicates': '"TMP"."ID"="BASE"."ID"', 'cardinality': 2164, 'projection': '(#keys=1) "BASE"."ID"[NUMBER,22], "BASE"."CREATION_TIME"[TIMESTAMP,11]', 'time': 1, 'cost': 9225, 'depth': 3, 'bytes': 86560, 'id': 3, 'cpu_cost': 1983805801},

                {'operation': 'JOIN FILTER', 'position': 1, 'parent_id': 3, 'object_owner': 'SYS', 'cardinality': 2219, 'projection': '"BASE"."ID"[NUMBER,22], "BASE"."CREATION_TIME"[TIMESTAMP,11]', 'object_name': ':BF0000', 'time': 1, 'cost': 662, 'options': 'CREATE', 'depth': 4, 'bytes': 59913, 'id': 4, 'cpu_cost': 223290732},

                    {'operation': 'HASH JOIN', 'position': 1, 'parent_id': 4, 'access_predicates': '"T"."OBJECT_ID"="BASE"."ID"', 'cardinality': 2219, 'projection': '(#keys=1) "BASE"."ID"[NUMBER,22], "BASE"."CREATION_TIME"[TIMESTAMP,11]', 'time': 1, 'cost': 662, 'options': 'RIGHT SEMI', 'depth': 5, 'bytes': 59913, 'id': 5, 'cpu_cost': 223290732},

                        {'operation': 'TABLE ACCESS', 'position': 1, 'filter_predicates': '"T"."SUBJECT_ID"=TO_NUMBER(:A__SUBJECT_ID) AND ("T"."RIGHTS"=\'r\' OR "T"."RIGHTS"=\'w\')', 'parent_id': 5, 'object_type': 'TABLE', 'object_instance': 8, 'cardinality': 2219, 'projection': '"T"."OBJECT_ID"[NUMBER,22]', 'object_name': 'OBJECT_RIGHTS', 'time': 1, 'cost': 5, 'options': 'FULL', 'depth': 6, 'bytes': 24409, 'optimizer': 'ANALYZED', 'id': 6, 'cpu_cost': 1823386},

                        {'operation': 'TABLE ACCESS', 'position': 2, 'parent_id': 5, 'object_type': 'TABLE', 'object_instance': 6, 'cardinality': 753862, 'projection': '"BASE"."ID"[NUMBER,22], "BASE"."CREATION_TIME"[TIMESTAMP,11]', 'object_name': 'PROFILES', 'time': 1, 'cost': 654, 'options': 'FULL', 'depth': 6, 'bytes': 12061792, 'optimizer': 'ANALYZED', 'id': 7, 'cpu_cost': 145148296},

                {'operation': 'VIEW', 'position': 2, 'parent_id': 3, 'object_instance': 3, 'cardinality': 735296, 'projection': '"TMP"."ID"[NUMBER,22]', 'time': 1, 'cost': 8559, 'depth': 4, 'bytes': 9558848, 'id': 8, 'cpu_cost': 1686052619},

                    {'operation': 'SORT', 'position': 1, 'parent_id': 8, 'cardinality': 735296, 'projection': '(#keys=1) MIN("SURNAME")[50], "PROFILE_ID"[NUMBER,22]', 'time': 1, 'cost': 8559, 'options': 'ORDER BY', 'temp_space': 18244000, 'depth': 5, 'bytes': 10294144, 'id': 9, 'cpu_cost': 1686052619},

                        {'operation': 'HASH', 'position': 1, 'parent_id': 9, 'cardinality': 735296, 'projection': '(#keys=1; rowset=200) "PROFILE_ID"[NUMBER,22], MIN("SURNAME")[50]', 'time': 1, 'cost': 8559, 'options': 'GROUP BY', 'temp_space': 18244000, 'depth': 6, 'bytes': 10294144, 'id': 10, 'cpu_cost': 1686052619},

                            {'operation': 'JOIN FILTER', 'position': 1, 'parent_id': 10, 'object_owner': 'SYS', 'cardinality': 756586, 'projection': '(rowset=200) "PROFILE_ID"[NUMBER,22], "SURNAME"[VARCHAR2,50]', 'object_name': ':BF0000', 'time': 1, 'cost': 1202, 'options': 'USE', 'depth': 7, 'bytes': 10592204, 'id': 11, 'cpu_cost': 190231639},

                                {'operation': 'TABLE ACCESS', 'position': 1, 'filter_predicates': 'SYS_OP_BLOOM_FILTER(:BF0000,"PROFILE_ID")', 'parent_id': 11, 'object_type': 'TABLE', 'object_instance': 5, 'cardinality': 756586, 'projection': '(rowset=200) "PROFILE_ID"[NUMBER,22], "SURNAME"[VARCHAR2,50]', 'object_name': 'NAMES', 'time': 1, 'cost': 1202, 'options': 'FULL', 'depth': 8, 'bytes': 10592204, 'optimizer': 'ANALYZED', 'id': 12, 'cpu_cost': 190231639}

cx_Oracle输出(似乎按id排序):

ID,    Created,    rownum
(1829, 2016-08-24, 1)
(2438, 2016-08-24, 2)

SQLDeveloper输出(按姓氏排序,按预期方式):

ID,      Created,    rownum
(518926, 2016-08-28, 1)
(565556, 2016-08-29, 2)

Answer 1

我没有看到ORDER BY会影响查询结果排序的子句.在SQL中,保证结果集排序的唯一方法是为ORDER BY最外层设置一个子句SELECT.

在几乎所有情况下,ORDER BY子查询中的a不一定受到尊重(Oracle rownum在查询的下一级别进行比较时会出现异常- 甚至在支持的情况下现在已经过时了FETCH FIRST <n> ROWS).

因此,没有理由认为一个ORDER BY在最里面的子查询会产生什么影响,特别是与JOIN那接下来会发生.

建议:

• 移动ORDER BY到最外面的查询.
• FETCH FIRST如果您使用的是Oracle 12c +,请使用语法.
• 移动ORDER BY 后的JOIN.
• 用ROW_NUMBER()而不是rownum.