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MyBatis 1. forEach cycle The attributes of   forEach element mainly include item, idnex, collection, open, separator, close. collection: incoming List or Array or self encapsulated Map. item: alias of the element iteration in the collection. idnex: index of element iteration yes in the collection. open: where is followed by what to start ...

Continue the part of execution plan that was not completed last time6. The possible indexes used by possible keys. This understanding indicates the possible indexes used in query. It may be used, but not necessarily. If it is empty, there must be no relevant index. But if there is value, it may not be used.7. Index actually used by key.Let's l ...

The process of R & D often involves database changes, the repair of table structure and the modification of data. In order to ensure that each environment can be changed correctly, we may need to maintain a database upgrade document to save these records. The environment that needs to be upgraded will be upgraded according to the document. ...

Problem description issue A: after turning on the parameter (phoenix.stats.enabled=true), use Phoenix SQL to query the data, and there are duplicates (the data found is more than the actual content stored in HBase) issue B: after the parameter is closed (phoenix.stats.enabled=false), Phoenix SQL performance decreases. Environmental Science Phoe ...

Creation of experiment table Table field description: id:Employee numbername: Employee nameano: Manager No create table admin(id varchar2(4),name varchar2(10),ano varchar2(4)); insert into admin values('001','XiongDa','004'); insert into admin values('002','XiongEr','004'); insert into admin values('003','ZhangSan','003'); insert into admin ...

This article solves the problem of Spring executing SQL script (file). The scene description can be ignored. Scenario Description: When I run a single test, that is, when the Spring project is started, Spring will execute classpath:schema.sql (explained later). I want to use this to solve a problem: Run multiple test files at a time, and each f ...

Change the large running table to a partitioned table The code of this article is limited to monthly horizontal partition based on data time. Other requirements can be implemented by modifying the code 1. Create a partition table The table field of this table is the same as that of the original table, with partition CREATE TABLE `metric_data_tm ...

spring boot uses logback by default. I've seen many places saying that logback consumes more performance than log4j. I haven't tried it, but I still use log4j more personally.   Look at pom dependency first <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter ...

JDBC introduction The full name of JDBC is java data base connectivity, which can provide unified access to a variety of databases. JDBC is a set of database access programming interface developed by sun, which is a SQL level API. It is written by java language, so it has good cross platform characteristics. The database application written by ...

Master Note: Troubleshooting guide for Automatic Undo Management (Doc ID 1579081.1) APPLIES TO: Oracle Database - Enterprise Edition - Version 9.2.0.1 to 12.1.0.1 [Release 9.2 to 12.1]Information in this document applies to any platform. PURPOSE This is a Master Note for troubleshooting the various issues reported on Undo Management. This docu ...