Mybatis source learning (25)-StatementHandler parsing

I. Introduction The    StatementHandler is one of the most core interfaces of Mybatis. He has completed the work related to the interaction between Mybatis and database (the interaction between Mybatis and JDBC on Statement). StatementHandler is mainly used for: Create Statement object Bind ...

Posted by robsgaming on Sat, 18 Jan 2020 07:07:33 +0100

Python Crash Course Reading Notes - Chapter 6: DICTIONARIES

A dictionary in Python is a collection of key:value pair s.Similar to Map or lookup table s in other languages. The key must be a string, and the value can be any object. Both key and value can use variables. Simple Dictionary student = {'name': 'tony', 'age': 14} print(student ['name']) print(studen ...

Posted by Mortier on Thu, 16 Jan 2020 02:10:34 +0100

JDBC principle and basic operation

1. JDBC principle 1. JDBC API: provides various operation providers, connection statement Preparedstatement resultset; 2. JDBC Driver Manager: manage different data drivers; 3. All kinds of database drivers: database drivers provided by corresponding database manufacturers, which link to directly oper ...

Posted by TapeGun007 on Mon, 13 Jan 2020 14:06:30 +0100

Consumption and simple optimization of the number of Oracle database connections

Observe the indicators and check the connection consumption --View session session: select * from v$session where username is not null select username,count(username) from v$session where username is not null group by username --View current connections select count(*) from v$process; --View maximu ...

Posted by Sulman on Mon, 13 Jan 2020 12:49:36 +0100

SQL: A pit for inserting data

Inserting data is often required in SQL Server, whether stored procedures or custom functions.When inserting data, many people choose the following INSERT INTO DestinationTable SELECT Column1,Column2,<column3 ,> FROM SourceTable This insertion usually doesn't cause any problems, but when the table fields of the Destinat ...

Posted by wolfrat on Fri, 10 Jan 2020 19:23:06 +0100

Work summary - get the sub nodes of the tree and copy the tree

1: Structure of tree nodes class KprDimension{ private String id; //Current node id of the tree private String name; //Tree node name private String parentId;// Tree node parent id private Integer level; //The node level of the tree, as shown in the figure below, A is 1, B,C is 2 private List<KprDimension> children;// ...

Posted by porrascarlos80 on Fri, 10 Jan 2020 09:04:15 +0100

A detailed explanation of the usage of execute immediate and DBMS SQL

1. Use scenario Both DBMS SQL package and EXECUTE IMMEDIATE in oracle can be used to parse and execute / dynamic SQL statements or PL/SQL blocks created at non runtime. In comparison, EXECUTE IMMEDIATE is relatively simple to use and can meet more common needs. 1.1 basic data CREATE TABLE stu( ID NUMBER(10), xm V ...

Posted by nova on Sun, 05 Jan 2020 13:40:36 +0100

Scala notes (5): MySQL database configuration and scala programming

MySQL database installation configuration In order to see / operate the database easily and intuitively, Navicat Premium software is generally installed to support multiple databases. There is not much nonsense in the installation process, mainly referring to the following connections, no pit in hand test, which are the main ...

Posted by aleph_x on Sat, 04 Jan 2020 02:29:12 +0100

MySQL paging query optimization case

On December 25, when viewing the monitoring of a customer, it was found that the customer had executed page by page queries for more than 60s. The execution status is as follows: This is a very simple and typical page query SQL. khome_space.regdate column has an index, and the table has more than three million rows of data. The offset of the q ...

Posted by paulsiew2 on Sat, 04 Jan 2020 00:08:17 +0100

JOIN and UNION in SQL

Building tables Create table tb and insert data: CREATE TABLE `tb_clazz` ( `id` int(11) unsigned NOT NULL AUTO_INCREMENT COMMENT 'class id', `grade` varchar(64) DEFAULT NULL COMMENT 'Class name', PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8mb4; INSERT INTO `tb_clazz` (`id`, `grade`) VALUES ...

Posted by gabrielkolbe on Thu, 02 Jan 2020 13:53:07 +0100