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DML包括那些操作
Data manipulation language (DML) statements query or manipulate data in existing schema objects. They enable you to:Retrieve data from one or more tables or views (SELECT); fetches can be scrollable...
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START WITH and CONNECT BY用法
The start with .. connect by clause can be used to select data that has a hierarchical relationship (usually some sort of parent->child (boss->employee or thing->parts). SQL> create table test_connec...
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用一条sql创建一个日历（转）
SELECT LPAD( MONTH, 20-(20-LENGTH(MONTH))/2 ) MONTH,"Sun", "Mon", "Tue","Wed", "Thu", "Fri", "Sat"FROM (SELECT TO_CHAR(dt,'fmMonthfm YYYY') MONTH,TO_CHAR(dt+1,'iw') week,MAX(DECODE(TO_CHAR(dt,'d'),'1'...
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循序渐进hints--full
1.不加hints的情况下，由于在object_id列上创建了唯一索引，执行计划走的是索引。SQL> set autot on explainSQL> select count(*) from test where object_id=100; COUNT(*)---------- &nbs...
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去除空格的函数trim
有2个表，test1、test2，结构如下：SQL> desc test1; Name &n...
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巧用rman修改数据文件名
在添加一个数据文件时，由于终端的原因，导致数据文件名中包含了隐含字符，在操作系统和数据库里均无法以数据文件名定位数据文件，用rman对该数据文件进行重命名：1.获得该文件的file_idselect file_id from dba_d...
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循序渐进---hints－Hints for Optimization Approaches and Goals
ALL_ROWS FIRST_ROWS(n) CHOOSE RULE 1. ALL_ROWSSQL> SELECT /*+ ALL_ROWS */ count(*) from t; COUNT(*)---------- 500 Elapsed: 00:00:00.09&n...
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group by 子句学习
SQL> alter table demo add (no int); Table altered. SQL> desc demo; Name ...
