oracle中的常用函数

decode有点类似java中的switch case. 只能针对具体的值(往往是一些类型字段的值)做判断.不针对condition做判断.

一个计算是否投放(isok)的例子.

DECODE (

               b.istime,

               1,

               DECODE (  a.如果处于投放时间

                  b.isremain,

                  1,

                  DECODE (    b.如果帐户还有钱

                     a.check_status,

                     1,

                     DECODE (  c.如果广告的状态是已审核通过

                        a.ispause,

                        0,      

                        DECODE (a.isoptimize,   d.如果广告未暂停

                                0,

            DECODE (           e.如果广告未优化

               b.place,

               3,                   f.如果达到日限额.

                                   0,                   返回0

                                   1                    否则返回1

                                   ), 

                                0    e/否则为0

            ),

                        0    d/否则为0

                     ),

                     0  c/否则为0 

                  ),

                  0  b/否则为0

               ),

               0  a/否则返回0

            )

               AS isok,

又比如通过decode临时调整一些值的大小.比如type=6的搬家由于数据量较大,会影响到其它类型的上线.通过decode设置一些临时的值将type=6的类型放到了最后处理.

/* Formatted on 2011-8-3 16:02:55 (QP5 v5.114.809.3010) */
SELECT   *
  FROM   (  SELECT   p.ID,
                     p.AGENTID,
                     p.TYPE,
                     p.GRPID,
                     p.STEP,
                     p.ACCOUNTID,
                     a1.C_INDUSTRY AS INDUSID,
                     a1.C_COMPANY_NAME AS ACCOUNTNAME,
                     a2.C_COMPANY_NAME AS AGENTNAME,
                     a1.C_EMAIL AS ACCOUNTEMAIL
              FROM   (SELECT   grpid, minid, ntype
                        FROM   (  SELECT   o.grpid,
                                           MIN (o.id) AS minid,
                                           DECODE (o.TYPE,
                                                   6, 16,
                                                   2, 1,
                                                   3, 1,
                                                   o.TYPE)
                                              AS ntype
                                    FROM   cpc.cpcoperation o,
                                           cpc.account ac,
                                           cpc.bill bi
                                   WHERE   o.step = 0
                                           AND o.TYPE IN
                                                    (1,
                                                     2,
                                                     3,
                                                     4,
                                                     5,
                                                     6,
                                                     7,
                                                     8,
                                                     9,
                                                     10)
                                           AND o.accountid = ac.i_account_id
                                           AND o.accountid = bi.i_account_id
                                           AND ac.C_STATUS IN ('正常', '转换')
                                           AND O.CREATEDATE <=
                                                 SYSDATE - 0.03 / 24
                                           AND bi.I_REMAIN > 0
                                --AND MOD(o.grpid, 5) = {?}
                                GROUP BY   o.grpid,
                                           DECODE (o.TYPE,
                                                   6, 16,
                                                   2, 1,
                                                   3, 1,
                                                   o.TYPE)
                                ORDER BY   DECODE (o.TYPE,
                                                   6, 16,
                                                   2, 1,
                                                   3, 1,
                                                   o.TYPE),
                                           MIN (o.id))
                       WHERE   ROWNUM <= 60) op,
                     (SELECT   o.*,
                               DECODE (o.TYPE, 6, 16, 2, 1, 3, 1, o.TYPE)
                                  AS ntype
                        FROM   cpc.cpcoperation o
                       WHERE   o.step = 0
                               AND o.TYPE IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10)) p,
                     CPC.ACCOUNT a1,
                     CPC.ACCOUNT a2
             WHERE       op.grpid = p.grpid
                     AND op.ntype = p.ntype(+)
                     AND p.accountid = a1.i_account_id(+)
                     AND a1.i_agent_id = a2.i_account_id(+)
                     AND p.id IS NOT NULL
                     AND p.id = op.minid
                     AND (a1.C_STATUS = '正常' OR a1.C_STATUS = '转换')
          ORDER BY   op.ntype, op.minid, op.grpid)
 WHERE   ROWNUM <= 200

min,max函数的参数只有一个,一般是个列
greatest,leaest的参数可以是多个,比大小用这个.