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Execution order of SQL statement: FROM <left_table> ON <join_condition> <join_type> JOIN <right_table> WHERE <where_condition> GROUP BY <group_by_list> HAVING <having_condition> SELECT DISTINCT <select_list> ORDER BY <order_by_condition> LIMIT <limit_number> 1. LIMIT stateme ...

encapsulation BaseDao What if the parameter, quantity and type are not fixed? public class TestMethod { //First, method overload /*public int sum(int a) { return a; } public int sum(int a,int b) { return a+b; } public int sum(int a,int b,int c) { return a+b+c; }*/ //Method 2, put an arra ...

Original: Replication with restricted privileges https://mysqlhighavailability.com/replication-with-restricted-privileges/ By Pedro Figueiredo Guan Changlong background Before MySQL 8.0.18, the slave server performed replication transactions without checking permissions, so that the master server could get all the content. In fact, this mea ...

- Restore content to start Introduction to Mybatis Introduction to MyBatis What is MyBtis? MyBatis is an open source framework that simplifies and implements the Java data persistence layer. It abstracts a lot of JDBC redundant code and provides a simple and easy-to-use API and database interaction. MyBatis's predecessor was iBATIS, which ...

brief introduction Callable Callable is a class similar to Runnable. The main difference is that Callable can return results, but Runnable does not. FutureTask Simply put, FutureTask can be enabled, cancelled, and used with Callable and Runnable to determine whether the thread is complete. When used together with Callable, the return result can ...

Problem description An SQL was encountered in the optimization process: SELECT SUM(user_value) FROM user_log WHERE del_flag = 0 AND product_id = 2324 AND user_type = 1; Its implementation plan is as follows: *************************** 1. row *************************** id: 1 select_type: SIMPLE table: use ...

Recent business needs to change a table to an update statement because the only primary key relationship is set and the direct insert will be abnormal, so I changed all insert statements to update statements. 1. this is the sql file exported from a colleague's computer. prompt Importing table gams_jc_ ...

1. AR mode removes the automatic sorting function public function search($params) { $dataProvider = new ActiveDataProvider([     'query' => $query,     'sort' => false,    // Remove automatic sorting ]); 2. Scalar Query The corresponding table of Book model is book, and the parameter value o ...

I. analysis. From last article Day3_JDBC - Encapsulation of Addition, Deletion and Change Checks (BaseDao class) using DBUtils third-party tools As you can see, every method in the BaseDao class needs to pass in a type of entity class (that is, JavaBean type). If we inherit the BaseDao class, we tell ...

JDBC: Java DateBase Connectivity Essence: JDBC is an official set of specifications, interfaces for connecting database operations. The code that actually runs is the code of the implementation class in the jar package provided by the database vendor. Example: 1. Importing jar packages Create a folder n ...