Oracle 由和（1=1或：edate为空）完成。通过这种方式，您可以利用OMG小马的“上下文变量”（在where子句中只有“有意义的”条件），而不需要它们的复杂性和创建上下文的必要性。在某些情况下，对于长时间运行的查询，完全消除绑定会更有效。但是这种情况很少见，如果

---

由

和（1=1或：edate为空）

完成。通过这种方式，您可以利用OMG小马的“上下文变量”（在where子句中只有“有意义的”条件），而不需要它们的复杂性和创建上下文的必要性。在某些情况下，对于长时间运行的查询，完全消除绑定会更有效。但是这种情况很少见，如果你不小心的话，你很容易受到SQL注入的攻击。我还没有听说过上下文变量，我认为它们可能对我正在研究的其他东西很有用（感谢你让我注意到它们！），但我仍然不清楚为什么在这种情况下它们比绑定变量更好。作为一个简单的例子，如果我的查询是：从CQV q中选择*其中q.bcode=sys_context（'ctx1'，'bcode'）与从CQV q中选择*其中q.bcode=：bcode，那么上下文变量方法比绑定变量有什么优势？区别在于当使用绑定变量时，查询中始终必须有bind变量引用。IE：如果值为null，则必须有

和：bcode为null

。使用上下文变量意味着不必包含无关/冗余的

WHERE

clausesha！我现在看到了！打开游标的代码取决于游标中有多少绑定变量，但是否使用上下文变量无关紧要！：）嗯，现在我需要和DBA谈谈，给我执行dbms_会话的权限。设置_上下文…@沮丧：一直在那里-我提供的信息&这两个链接过去对我有用：）

select num
from (select distinct q.num
       from cqqv q
       where q.bcode = '1234567' --this is variable
             and q.lb = 'AXCT' --this is variable
             and q.type = 'privt' --this is variable
             and q.edate > sysdate - 30 --this is variable
       order by dbms_random.value()) subq
where rownum <= 10; --this is variable

select num
from (select distinct q.num
       from cqqv q
       where q.bcode = '1234567' --this is variable
             and q.lb = 'AXCT' --this is variable
             --and q.type = 'privt' --this condition ignored because of "type=*" in input
             and q.edate > sysdate - 30 --this is variable
       order by dbms_random.value()) subq
where rownum <= 10; --this is variable

select num
from (select distinct q.num
       from cqqv q
       where 1=1
             and (:bcode is null or q.bcode = :bcode)
             and (:lb is null or q.lb = :lb)
             and (:type is null or q.type = :type)
             and (:edate is null or q.edate > :edate - 30)
       order by dbms_random.value()) subq
where rownum <= :numrows

declare
    rc sys_refcursor;
    q long;
begin
    q := 'select num
    from (select distinct q.num
           from cqqv q
           where 1=1';

    if p_bcode is not null then
        q := q || 'and q.bcode = :bcode';
    else
        q := q || 'and (1=1 or :bcode is null)';
    end if;

    if p_lb is not null then
        q := q || 'and q.lb = :lb';
    else
        q := q || 'and (1=1 or :lb is null)';
    end if;

    if p_type is not null then
        q := q || 'and q.type = :type';
    else
        q := q || 'and (1=1 or :type is null)';
    end if;

    if p_edate is not null then
        q := q || 'and q.edate = :edate';
    else
        q := q || 'and (1=1 or :edate is null)';
    end if;

    q := q || ' order by dbms_random.value()) subq
    where rownum <= :numrows';

    open rc for q using p_bcode, p_lb, p_type, p_edate, p_numrows;
    return rc;
end;

select num
from (select distinct q.num
       from cqqv q
       where 1=1
             and q.bcode = :bcode
             and q.lb = :lb
             and (1=1 or :type is null)
             and (1=1 or :edate is null)
       order by dbms_random.value()) subq
where rownum <= :numrows

and (:bcode is null or q.bcode = :bcode)

L_CURSOR SYS_REFCURSOR;
L_QUERY  VARCHAR2(5000) DEFAULT 'SELECT num
                                   FROM (SELECT DISTINCT q.num
                                           FROM CQQV q
                                          WHERE 1 = 1 ';
BEGIN

    IF IN_BCODE IS NOT NULL THEN
      DBMS_SESSION.SET_CONTEXT('THE_CTX',
                               'BCODE',
                               IN_BCODE);
      L_QUERY := L_QUERY || ' AND q.bcode = SYS_CONTEXT(''THE_CTX'', ''BCODE'') ';
    END IF;

    IF IN_LB IS NOT NULL THEN
      DBMS_SESSION.SET_CONTEXT('THE_CTX',
                               'LB',
                               IN_LB);
      L_QUERY := L_QUERY || ' AND q.lb = SYS_CONTEXT(''THE_CTX'', ''LB'') ';
    END IF;

    IF IN_TYPE IS NOT NULL THEN
      DBMS_SESSION.SET_CONTEXT('THE_CTX',
                               'TYPE',
                               IN_TYPE);
      L_QUERY := L_QUERY || ' AND q.type = SYS_CONTEXT(''THE_CTX'', ''TYPE'') ';
    END IF;

    IF IN_EDATE IS NOT NULL THEN
      DBMS_SESSION.SET_CONTEXT('THE_CTX',
                               'EDATE',
                               IN_EDATE);
      L_QUERY := L_QUERY || ' AND q.edate = SYS_CONTEXT(''THE_CTX'', ''EDATE'') - 30 ';
    END IF;

    L_QUERY := L_QUERY || ' ORDER BY dbms_random.value()) subq
           WHERE rownum <= :numrows ';

    FOR I IN 0 .. (TRUNC(LENGTH(L_QUERY) / 255)) LOOP
      DBMS_OUTPUT.PUT_LINE(SUBSTR(L_QUERY, I * 255 + 1, 255));
    END LOOP;

    OPEN L_CURSOR FOR L_QUERY USING IN_ROWNUM;
    RETURN L_CURSOR;

END;

DBMS_SESSION.SET_CONTEXT('THE_CTX', 'LB', IN_LB);

... L_QUERY USING IN_EXAMPLE_VALUE

select num
from (select distinct q.NUM
       from cqqv q 
       where  (q.bcode = :bcode) 
                  and  (1=1 or :lb is null) 
                  and  (1=1 or :type is null) 
                  and  (q.edate> :edate) 
                order by dbms_random.value()) subq 
where rownum <= :numrows

select num
from (select distinct q.num
       from cqqv q
       where q.bcode = '1234567' --this is variable
             and q.lb = 'AXCT' --this is variable
             and q.type = nvl(<variable-type>, q.type)  --this condition ignored because of "type=*" in input
             and q.edate > sysdate - 30 --this is variable
       order by dbms_random.value()) subq
where rownum <= 10; --this is variable