发现和上面的not exist差不多!你是不是又恢复对not in的信心了呢? 但是 deletefromtb_scwhere(studentid,courseid,score)notin(selectstudentid,courseid,max(score)asscorefromtb_scgroupbystudentid,courseid) 确实是慢得让人发指,而将delete换成select之后,却并不慢,不信大家请执行下面sql: selecta.*fromtb...
1、用EXISTS替代IN,NOT EXISTS替代NOT IN:在子查询中,NOT 在许多基于基础表的查询中,为了满足一个条件,往往需要对另一个表进行联接.在这种情况下, 使用EXISTS(或NOT EXISTS)通常将提高查询的效率. 1. SELECT*FROMEMP (基础表) WHEREEMPNO>0ANDEXISTS(SELECT‘X' FROM DEPT WHERE DEPT.DEPTNO = EMP.DEPTNO A...
发现和上面的not exist差不多!你是不是又恢复对not in的信心了呢? 但是 deletefromtb_scwhere(studentid,courseid,score)notin(selectstudentid,courseid,max(score)asscorefromtb_scgroupbystudentid,courseid) 1. 确实是慢得让人发指,而将delete换成select之后,却并不慢,不信大家请执行下面sql: selecta.*fr...
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OracleSQLSQL MacrosSQL macros7. August 2024 For me, building efficient data pipelines means thinking about performance from day one. And that means a conscious and thoughtful approach to optimizer statistics. It is not just this Autotask, which always runs in the database in the evenings or at...
SQL> select * from t2 where not exists (select 1 from t1 where t1.c2=t2.c2); C1 C2 --- --- 1 3、结论 in和exists结果相同(都会排除掉null,无论内部表中有无null) not in会过滤掉外部表中的null(即使内部表中无null) not exists不会过滤掉外部...
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PLSQL 提供了一种异常错误的处理机制,可以帮助实现对错误的捕获和处理。 二、常见异常 (1)ACCESS_INTO_NULL :程序试图为未初始化对象的属性赋值。 (2)CASE_NOT_FOUND : 语句子句中的任何选项均未被选中,并且没有子句。 (3)COLLECTION_IS_NULL:程序试图将 EXISTS 以外的收集方法应用于未初始化的嵌套表或 varra...
SQL> CREATE TABLE yashan.COR_xxx_xxx_MAINT_xxx 2 ( 3 COM_ID NUMBER(10) NOT NULL, 4 OFFER_ID NUMBER(10) NOT NULL, 5 xxxx_CODE NUMBER(10) NOT NULL, 6 xxxx_LEVEL NUMBER(1) NOT NULL, 7 OTHER_xxxx_CODE VARCHAR2(255 CHAR) NULL, ...