Oracle | 易学教程

Changes in database session context persists with pooled connection reuse

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问题 In my application I have multithreads that needs to access database and I am using apache.tomcat.jdbc.pool.DataSource as a JDBC connection pool. In some cases users execute stored procedures that might affect the database session context/variables before executing another query to retrieve some data. After a thread is finished, connection is closed but the way the pooled connections work, the connection is not actually closed but rather returned to the connection pool for reuse. The problem

How to get a list of native Oracle Functions Like (NVL, ABS etc)

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问题 I've trying with this command bellow, but does not work as i expected: select OBJECT_NAME, OWNER from SYS.ALL_OBJECTS where upper(OBJECT_TYPE) = upper('FUNCTION') order by OWNER, OBJECT_NAME is there any way to achieve that? 回答1: Check this one: select distinct PROCEDURE_NAME from ALL_PROCEDURES where OWNER = 'SYS' and OBJECT_NAME = 'STANDARD'; 来源： https://stackoverflow.com/questions/47200895/how-to-get-a-list-of-native-oracle-functions-like-nvl-abs-etc

How to get the number of elements in a JSON array stored as CLOB with Oracle 12c?

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问题 I'm storing a java class A as A_DOC in a clob column in my database. The structure of A is like: { id : 123 var1: abc subvalues : [{ id: 1 value : a }, { id: 1 value :b } ... } ]} I know I can do things like select json_query(a.A_DOC, '$.subvalues.value') from table_name a; and so on, but how I'm looking for a way to count the number of elements in the subvalues array through an sql query. Is this possible? 回答1: You can use JSON_TABLE: SELECT id, var1, count(sub_id) subvalues FROM JSON_TABLE

Oracle timestamp to sql server DateTime

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问题 I have multiple statements from oracle database and I need to use them in SQL Server insert into COMENZI (NR_COMANDA, DATA, MODALITATE, ID_CLIENT, STARE_COMANDA, ID_ANGAJAT) values (2456, to_timestamp('08-11-1998 07:53:25.989889', 'dd-mm-yyyy hh24:mi:ss.ff'), 'direct', 117, 0, 163); insert into COMENZI (NR_COMANDA, DATA, MODALITATE, ID_CLIENT, STARE_COMANDA, ID_ANGAJAT) values (2457, to_timestamp('01-11-1999 09:22:16.162632', 'dd-mm-yyyy hh24:mi:ss.ff'), 'direct', 118, 5, 159); How can I

LISTAGG in ORACLE

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问题 I am trying to use LISTAGG() to fetch more than two columns. SELECT deptname, deptno, LISTAGG(ename, ',') WITHIN GROUP (ORDER BY ename) AS employees FROM emp GROUP BY deptno; But it is throwing this error: : FROM keyword not found where expected 00000 - "FROM keyword not found where expected" *Cause: *Action: Error at Line: 3 Column: 12 Can please somebody explain why it is? 回答1: The LISTAGG analytic function was introduced in Oracle 11g Release 2 . So, if you are on older version, you won't

Oracle timestamp to sql server DateTime

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内部类与静态内部类

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前言　　如果你是一个急性子，没什么耐性的人，可以只看下句，自己去品味理解：　　内部类：就是我是你的一部分，我了解你，我知道你的全部，没有你就没有我。（所以内部类对象是以外部类对象存在为前提的）　　静态内部类：就是我跟你没关系，自己可以完全独立存在，但是我就借你的壳用一下，来隐藏自己。　　如果还不知道静态和普通成员的区别，就先学static吧。　　静态成员：属于这个类，数据存放在class文件中，程序运行之前就已经存进去数据了。　　普通成员：属于这个类的对象，程序运行后生成堆栈中。　　先来看一下官方说法，根据Oracle官方的说法：　　 Terminology: Nested classes are divided into two categories: static and non-static. Nested classes that are declared static are called static nested classes . Non-static nested classes are called inner classes . 　　一个称为静态嵌套类（静态内部类），一个称为内部类。那么两者到底有什么区别呢？很多JDK源码用到了静态内部类。HashMap、ThreadLocal、AQS的sync等。那么接下来学习一下内部类吧！内部类　

win10中安装jdk1.8

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一、JDK下载两种方法，第一种是从官网下载；第二种是拿来主义，小拿直接给你网盘地址。不过，作为java新手，最好还是学会去官网下载。官网下载的文件才是最安全的，从不靠谱第三方下载有可能安装包有缺失或者干脆种点病毒木马神么的。再说，有可能哪天给别人装jdk或者自己升级jdk，找不到网盘地址又得回头点技能点了。百度（或其它搜索引擎）搜“jdk 下载”，正好第一个就是1.8的下载链接。 image 1. 点击进入下载页页面地址： https://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html 目前官方刚对1.8做了一次bug升级，强烈建议使用191或者192的小版本，这里就选择8u191. image 2. 先选中上方的接受协议，再选择适合自己操作系统的包我们这里选择最后一个windows64位的安装包，点击红框内右边的jdk-8u191-windows-x64.exe就可以下载了。二、jdk安装现在jdk的安装比网上各种文章简单多了，我们来动手搞定它。 1. 双击下载的exe文件，开始安装。如下图，点击下一步。 image 2. 选择jdk的安装目录，建议大家就算不使用默认路径，也放在C盘，除非你的C盘空间告急。 image 3、直接点击下一步，出现下图的告警信息。

win10 mysql5.7忘记密码如何解决

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点击开始菜单，搜索cmd.exe，左击以管理员身份运行操作之前先备份好数据库（切忌） C:\Users\Administrator>cd C:\Program Files\MySQL\MySQL Server 5.7 \bin C:\Program Files\MySQL\MySQL Server 5.7 \bin>mysqld --skip-grants- tables //发现不成功，原因是没有data目录，于是在此C:\Program Files\MySQL\MySQL Server 5.7目录下创建了data目录，成功执行且可以跳过认证 //但是进入数据库发现原来的库都不见了，原来是默认情况下，MySQL的数据库文件是保存在C:/ProgramData/mysql/MySQL Server 5.7/Data/ 而且，Win7，Win10缺省是把C:/ProgramData目录隐藏的。 //因此我们需要指定配置文件来启动 C:\Program Files\MySQL\MySQL Server 5.7 \bin>mysqld --defaults- file = " C:\ProgramData\MySQL\MySQL Server 5.7\my.ini " --user=mysql --skip-grants-tables //进入数据库 C:\Program Files

Oracle Database change notification

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问题 I am new to DCN, can I use it to detect updates on a column in my table along with inserts in that table ? I am referring to this 回答1: Yes, you can - Change Notifications made for that. You need to register СN listener with query to watch (it can a whole table select * from your_table or part of it select column1 from your_table where column2='xxx' ) and callback function . You should understand that it is async mechanism changes will not detect immediately, but after some time. Your

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