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introduction In actual business development, data interaction between multiple tables is often involved. At this time, single table query can no longer meet complex business requirements, so multi table connection query is needed; Connection query is mainly divided into the following three types: Inner connection Equivalent connectionNon ...

catalogue Normal execution of transactions Abandon transaction Compiled exception Runtime exception (I/O) Monitor} Watch (frequently asked in interview) redis monitoring test Normal execution succeeded!   Test multithreading to modify the value. Using watch can be used as redis optimistic lock operation Jedis Test: 1. Import cor ...

query Simple query Query all mysql: SELECT e.* From emp e oracle: SELECT e.* From emp e; Query specific columns mysql: SELECT e.empno,e.ename,e.job from emp e oracle: SELECT e.empno,e.ename,e.job from emp e Alias use mysql: select e.empno 'Employee number',e.ename 'Employee name',e.job 'Employee position',e.mgr 'Superior ...

Case 1: Deployment redis colony Case 2: Management redis colony 12 1 case 1: deploying redis cluster 1.1 problems Specific requirements are as follows: Prepare cluster environment install redis And create a cluster View cluster information 1234 1.2 scheme Build a redis cluster. The topology plan is show ...

premise Process multiple business modules at the same time. Multiple business modules may need to transfer data to each other or need synchronous control. Two entities need to communicate with each other and must have resources that can be shared. Files on disk: -- > IO processing is slow and out of sync. Application scenario of process co ...

system configuration Detect and close system swap This section describes how to close swap. TiDB needs enough memory to run, and swap is not recommended as a buffer with insufficient memory, which will reduce performance. Therefore, it is recommended to permanently shut down the system swap and do not use the swapoff -a mode to shut down, oth ...

1, Quick start 1. Check the health status of the cluster http://localhost:9200/_cat http://localhost:9200/_cat/health?v Note: v is used to require the header to be returned in the result Status value description Green - everything is good (cluster is fully functional) Yellow - all data is available but some replicas are not yet alloca ...

4. DQL query data (most important) 4.1,DQL Data Query Language All query operations use it to SELECT It can do simple query and complex query~ The core language and the most important statement in the database Most frequently used statements SELECT statement syntax SELECT [ALL | DISTINCT | DISTINCTROW ] [HIGH_PRIORITY] [STRAIGHT_ ...

springboot integration jpa entry The entry case writes a crud of jpa single table 1. Prepare the springboot project Introduce dependency pom.xml <?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache ...

1, Questions for each course Use an SQL statement to query the student table and the names of students with more than 80 points in each course. Solution 1: having Idea: if the minimum course score is greater than 80 points, then all his course scores must be greater than 80 points! code implementation SELECT name FROM xuesheng GROUP BY n ...