SQL - UNION

union all
Merge all column with same no. of column (Diff type would be OK but may loss some data) 

union
Like union all but will remove duplicated rows like distinct










 

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REMOVE JAVA SDK

  sudo rm -fr /Library/Internet\ Plug-Ins/JavaAppletPlugin.plugin sudo rm -fr /Library/PreferencePanes/JavaControlPanel.prefPane sudo rm -fr ~/Library/Application\ Support/Oracle/Java cd /Library/Java/JavaVirtualMachines rm -fr /usr/local/opt/openjdk@11/libexec/openjdk.jdk sudo rm -rf ****.jdk
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JAVA - JPA

HIBERNATE hibernate.ddl-auto : create : will delete and create new table every startup , so will make data lost create-drop : same as create but will delete and create when session down and up update : create when first time and update every startup keep date validate : check and create/update tables every startp none : do noting JPA GeneratedValue(strategy = GenerationType.XXXXXX) the strategy of primary key TABLE: need to use with @TableGenerator  SEQUENCE: use Sequnce (like a temp table) ony Orcale , PSQL,DB2 support IDENTITY:  control by table(database) ORacle not support AUTO : Default ,control by springboot 在Hibernate中，提供了懒加载功能，当需要的时候才查询具体数据，但是在使用@OneToOne关系时， FetchType.LAZY看起来不会生效。 当你查询一个实体类A，这个实体类A持有另一个实体类B的引用，但是A中并没有记录B的主键，这种情况下，即使有懒加载注解，查询实体A的时候依然会执行两条SQL，分别查询实体类A和B对应的表A和表B。这是由于Hibernate的机制导致，并不是你的使用方式有问题或者存在其他bug。 ———————————————— 版权声明：本文为CSDN博主「_古井心」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。 原文链接：https://blog.csdn.net/u010234516/article/details/103011494
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MAP - Sort with stream

 LEETCODE 1636 Given an array of integers   nums , sort the array in   increasing   order based on the frequency of the values. If multiple values have the same frequency, sort them in   decreasing   order. Return the  sorted array . Example 1: Input: nums = [1,1,2,2,2,3] Output: [3,1,1,2,2,2] Explanation: '3' has a frequency of 1, '1' has a frequency of 2, and '2' has a frequency of 3. Example 2: Input: nums = [2,3,1,3,2] Output: [1,3,3,2,2] Explanation: '2' and '3' both have a frequency of 2, so they are sorted in decreasing order. Example 3: Input: nums = [-1,1,-6,4,5,-6,1,4,1] Output: [5,-1,4,4,-6,-6,1,1,1] #1 class Solution { public int[] frequencySort(int[] nums) { return Arrays.stream(nums) .boxed() // boxing to wapped class .collect(Collectors.toMap(e-> e , e-> 1 , Integer::sum))//?? .entrySet() .stream() .sorted((e1,e2) -> e1.getValue().equals(e...
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