Programmer Think

🎈 Write in front 🙋‍♂️ Hello everyone, I'm super dream. You can call me Xiaomeng~ It's time to practice SQL again! Let's study together! 🙋‍♂️ If you don't understand anything in the learning process, you are welcome to leave a message and ask questions in the comment area. Xiaomeng will tell you everything. catalogue 🌌 ...

01. Add, delete and modify insert record SQL1 insert record (I) Now there are two users' response records, as follows: User 1001 began to answer test paper 9001 at 10:11:12 p.m. on September 1, 2021, and submitted it 50 minutes later, with 90 points;User 1002 began to answer test paper 9002 at 7:1:2 a.m. on September 4, 2021, and quit the p ...

User information table: user_profile Device ID (device_id) gender age School (university) active_days_within_30 field Post quantity field (question_cnt) Answer quantity field (answer_cnt) iddevice_idgenderageuniversitygpaactive_days_within_30question_cntanswer_cnt12138male21Peking University3.4721223214maleNULLFudan University4155253654 ...

Absrtact: paging query is required to turn the page of posts, and paging query is also required to search goods. When there are tens of millions or hundreds of millions of data, how can we quickly pull the full amount of data? This article is shared from Huawei cloud community< Paging query for large data volume performance optimization &g ...

There are five ways to obtain database connection:     Method 5 [final version] only this one can be practiced (doge): Put the basic information into a configuration file.   Benefits of mode 5: 1. Realize the separation of data and code, and realize decoupling 2. If you need to modify the configuration file information, you ...

preface This article belongs to the column big data technology system, which was originally created by the author. Please indicate the source of quotation. Please point out the deficiencies and errors in the comment area. Thank you! Please refer to the table of contents and references of this column Big data technology system catalogu ...

Window Join # Streaming media Window connection adds the time dimension to the connection standard itself. In doing so, the window join connects the elements of two streams that share a common key and reside in the same window. Semantics and of window connection The semantics of DataStream window connection are the same For streaming queries ...

Inquiry # The SELECT statement and VALUES statement are TableEnvironment This method takes the result of the SELECT statement (or VALUES statement) as a Table ATable can be used for Subsequent SQL and Table API queries，Convert to DataStream or Write TableSink . SQL and Table API queries can be seamlessly mixed, optimized as a whole and conve ...

Before that, we learned the global configuration file of mybatis. Now we begin to learn the mapping file of mybatis. In the mapping file, you can write the following top-level element labels: cache – Cache configuration for this namespace. cache-ref – Cache configuration that references other namespaces. resultMap – Describing how to load obje ...

10. Multi table query of mybatis Relational database tables are divided into * one-on-one * One to many * Many to many give an example The ID number is one to one. A person can only have one ID number. An ID number can only belong to one person.Users and orders are one to many, and orders and users are many to one One user can place multip ...