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DQL data query language multi-table query Cartesian set Equivalence / connection query join query join link Common functions Subquery Paging query multi-table query Cartesian set Generation conditions: Omit connection conditions Invalid connection condition All rows in all tables are connec ...

New feature of JDK8: date time related API Problems with old version date time API: 1. Poor design: in java.tilogjava Sq| has date classes in its packages, java.util.Date Contains both date and time, and java.sql.Date Only. Contains the date. In addition, the classes used for formatting and pars ...

1, Cache overview The design of Mybatis cache system follows the principle of single responsibility, opening and closing, and high decoupling. It is exquisite and fully layered, and its unique features can be applied to many similar businesses. Here is a brief analysis of the main caching system. With the help of the learning of Mybatis cache ...

example: At present, there are three tables A, B and C. among them, A and B are one to many relationships, and B and C are one to many relationships. Now it is necessary to save the primary key of table A in B into C; The general idea is to query out B and update table C with an update statement, bu ...

QuerySet API usage QuerySet can construct, filter, slice, and approximate results without actually accessing the database. Unless you do something to evaluate the query set, no query activity actually occurs to the database. (1) Basic properties iteration The QuerySet is iterative, and its databa ...

JDBC advanced Use of JDBC connection pool The concept of database connection pool Database connection is a key and limited resource. When java program and database get the connection, it consumes resources especially. Therefore, a database connection pool is created to manage the connection betwe ...

SQL Server advanced query and T-SQL programming to realize warehouse inventory management system SQL Server advanced query and T-SQL programming SQL Server advanced query and T-SQL programming to realize warehouse inventory management system 1. Language and environment 2. Functional requirements 3 ...

catalog 1, Sqoop export 2, Sqoop import 1, Sqoop export 1. Create a job to export the HDFS file to the MySQL database. (1) Open PDI and create a new job, as shown in Figure 1. Figure 1   (2) Edit the 'Sqoop export' job item, as shown in Figure 2. Figure 2 Description: CDH631 is a buil ...

I was asked hundreds of times about IoC and AOP in my last interview, and I was still silly and confused?We understand the two ideas of IOC and AOP. Next, let's not consider how Spring achieves these two ideas. First, through a case of bank transfer, we analyze the code level problems in this case.Use our existing knowledge to solve these prob ...

LINQ in C ා provides two operation modes: query expression and query operator. All query expressions are replaced by corresponding query operator classes. Query expression is a bit of "class" SQL. When writing SQL in the code, I always feel that it is not "elegant". Using query operators is "elegant". This series i ...