Oralce9 的新方法： Merge into Using

一、语义

　　MERGE语句是Oracle9i新增的语法，用来合并UPDATE和INSERT语句。通过MERGE语句，根据一张表或子查询的连接条件对另外一张表进行查询，连接条件匹配上的进行UPDATE，无法匹配的执行INSERT。这个语法仅需要一次全表扫描就完成了全部工作，执行效率要高于INSERT＋UPDATE。 

二、语法结构

MERGE [INTO [schema .] table [t_alias] 
USING [schema .] { table | view | subquery } [t_alias] 
ON ( condition ) 
WHEN MATCHED THEN merge_update_clause 
WHEN NOT MATCHED THEN merge_insert_clause;

三、应用例子

--例子一：
 MERGE INTO TEMP_CD_CNTR_QUERY A USING CONTAINER B
         ON (A.CNTR_NUM=B.EQMT_NUM and B.State='Active')
         WHEN MATCHED THEN
         UPDATE SET A.CNTR_NUM_CHECK=CASE WHEN B.CHECK_DIGIT IS NULL OR B.CHECK_DIGIT=''
                        THEN   A.CNTR_NUM
                        ELSE   A.CNTR_NUM||B.CHECK_DIGIT
                         END ,
                        A.CNTR_TYPE=B.oocl_Cde;
--例子二：

         MERGE INTO TEMP_CD_CNTR_QUERY A USING (SELECT DISTINCT t.TRCKG_GRP_REF_CDE,t.CURRENT_CNTR_NUM,t.CONSLD_PACKG_REF_CDE FROM CGO_PACKAGE t) B
         ON (A.TRCKG_GRP_REF_CDE=B.TRCKG_GRP_REF_CDE and A.cntr_num = B.CURRENT_CNTR_NUM AND B.CONSLD_PACKG_REF_CDE IS NOT NULL)
         WHEN MATCHED THEN
         UPDATE SET A.IS_PATIAL= B.CONSLD_PACKG_REF_CDE;