mysql | 易学教程

JSONException: No value for id

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问题 It reads and writes fine from the database but gives the JSONException error. Any help would be greatly appreciated! Thank you 回答1: This error happens in getter functions of a JSONObject and it means that you are trying to retrieve a value from the JSONObject using an id that doesn't exist in the JSONObject. Before retrieving a value, check if it actually exists in the JSONObject by the has(String name) method or using the opt methods. For more information about the JSONObject class see here.

mysql select single column as single dimension array in PHP

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问题 I'm selecting a single column from my mysql database: $savedSQL = 'SELECT can_id FROM savedsearches WHERE user_id = "'.mysql_real_escape_string($user_id).'" AND insertTime >= "'.$lastSigTime.'"'; $savedQuery = mysql_query($savedSQL); And I'd like to return the values as a single dimension, enumerated array such that array[0] = row1, array[1] = row2, etc. When I put it into an array like this: while($savedResult = mysql_fetch_array($savedQuery)) { $savedArray[] = $savedResult; } It returns it

第五章 FISCO BCOS 区块链浏览器的部署

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想了解相关区块链开发，技术提问，请加QQ群：538327407 前提前面我们已经通过底层部署、sdk调测、自定义智能合约编写与部署、联合单元测试调测，已经初步对FISCO BCOS的区块链底层和实际开发有了简单了解。接下来，在本文中，你可以看如何在底层部署区块链浏览器，并对区块链浏览器进行配置，从而实现图形化区块链浏览。正常流程 1、官方文档通过以下链接，可以先查看一下官方对于区块链浏览器的部署 https://github.com/FISCO-BCOS/fisco-bcos-browser/tree/master/deploy 2、环境准备 2.1 Java环境部署此处给出简单步骤，供快速查阅。更详细的步骤，请参考官网。（1）从官网下载对应版本的java安装包，并解压到相应目录 mkdir / software tar -zxvf jdkXXX.tar.gz /software/ 本次demo使用：tar -zxvf jdk-8u211-linux-x64.tar.gz （2）配置环境变量使用命令打开/etc/profile文件 sudo vi /etc/profile export JAVA_HOME=/software/jdk1. 8 .0_121 export PATH =$JAVA_HOME/ bin:$PATH export CLASSPATH =

2019 最新阿里天猫、蚂蚁、钉钉ava 面试题汇总，附答案

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Java面试前需要做足各方面的准备工作，肯定都会浏览大量的面试题，本人也不例外，这是一些最新面试题，分享给大家。 Java基础面向对象的特征：继承、封装和多态 int 和 Integer 有什么区别； Integer的值缓存范围说说反射的用途及实现 Http 请求的 GET 和 POST 方式的区别 MVC设计思想什么是Java序列化和反序列化；如何实现Java序列化；重载和重写的区别进程和线程线程和进程的概念并行和并发的概念创建线程的方式及实现进程间通信的方式说说 CountDownLatch、CyclicBarrier 原理和区别说说 Semaphore 原理说说 Exchanger 原理 ThreadLocal 原理分析； ThreadLocal为什么会出现OOM，出现的深层次原理讲讲线程池的实现原理线程池的几种实现方式线程的生命周期；状态是如何转移的锁机制什么是线程安全？如何保证线程安全？重入锁的概念；重入锁为什么可以防止死锁？产生死锁的四个条件如何检查死锁 volatile 实现原理 synchronized 实现原理（对象监视器） synchronized 与 lock 的区别 AQS 同步队列 CAS 无锁的概念；乐观锁和悲观锁常见的原子操作类什么是 ABA 问题；出现 ABA 问题 JDK 是如何解决的

mysql主从复制

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一、主从复制原理： 1、过程 1）<master>将数据写入数据文件，将sql语句写入binlog 2）<slave>通过IO 线程带着用户名、密码、读取的binlog日志名、位置连接到<master>。并取走所需的sql语句和binlog的位置信息。 3）IO Thread 将binlog的位置信息存入master info，将sql语句写入 relay log。 4）SQL Thread 从relaylog中取出sql语句，有mysql写入数据库文件。 2、作用： 1）便于实现读写分离。 * 实时性高的数据在主服务器上查询 2）备份可在从服务器上执行。二、配置（一）配置my.cof 1. <master> #vim /etc/my.cnf [mysqld] server-id=150 #起个独有名字防止服务器混乱。 log-bin=mysql-bin #/开启binlog日志，起个名字 binlog-format=mixed #定义binlog日志格式 2.<slave> 打开relay log日志。（必须）打开binlog日志。（建议打开）为以后数据丢失做准备。 # vim /etc/my.cnf sever-id=132 log-bin=mysql-bin relay-log=mysql-relay log-slave-updates

how to save only time not date in database through sql query

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问题 this query is saving complete date and time. but i want to save only time not date in database. is there any query to do this? update table set current_time=now(); 回答1: Your column must be set to either DATETIME or TIMESTAMP. If you use the TIME type then your query would work as expected. If you are using any other type of column then you could use CURTIME() method or CAST(column AS TIME) as mentioned by other answers, however this would use more space on disk, and make for much slower

Using EF DbContext with mysql and sql in the same project

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问题 I'm working on an ASP.net MVC project using EF in combination with MySql. Now this works just fine on its own but I also want to reference another class library that uses EF with SQL. When I reference the library EF seems to get confused on what provider to use for each DbContext. On my MySql DbContext I have the following attribute in order to tell EF this DbContext should be handled by the MySql provider: [DbConfigurationType(typeof(MySql.Data.Entity.MySqlEFConfiguration))] Now on the SQL

Using EF DbContext with mysql and sql in the same project

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fetch_assoc returns last inserted elements

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问题 For some reasons mysql returns only last inserted element in table,could anyone give a tip what's wrong with my code? i'm just practicing php and trying to figure out best ways to make functions easily reusable(just practicing oop i mean). i know this is a bad way but it's only for practice purposes. <!DOCTYPE html> <html> <head> <title>Test Title</title> </head> <body> <?php class Database{ public $db; public function __construct($host,$username,$password,$dbname){ $this->db=new MySQLi($host

How to Get the Supervisor's Name instead of the UserID + INNER JOIN in MYSQL

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问题 Here are my tables : select * from user USERID NAME STATUS 1 AAA Member 2 BBB Member 3 CCC Supervisor 4 DDD Member 5 EEE Member select * from attendance NO DATE SUPERVISOR MEMBER 1 2019-12-11 3 1 2 2019-12-11 3 2 3 2019-12-11 3 4 4 2019-12-11 3 5 select * from detail NO USERID ATTENDANCE REASON 1 1 0 SICK 2 2 1 - 3 4 1 - 4 5 1 - The result I want : USERID DATE NAME REASON SUPERVISOR 1 2019-12-11 AAA SICK CCC 2 2019-12-11 BBB - CCC 3 2019-12-11 DDD - CCC 4 2019-12-11 EEE - CCC The SQL I've

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