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SQL multi table query #Alias table names SELECT st.class_num,cl.class_name FROM student st,class cl #Connection query Find out the class name of each student #The table on the left is the main table (the most used) SELECT st.class_num,cl.class_name FROM student st,class cl # the table on the right is the main table SELECT student.name,s ...

This article introduces the integration of spring boot and mybatis plus in the project. When writing query methods, lambda is used to represent query data. When actually executing sql, the where condition will be spliced with deleted = 0. Reason: 1. Delete field in global configuration. Default delete value = 1 Undeleted value = 0. The configu ...

The original content of GreatSQL community cannot be used without authorization. Please contact Xiaobian and indicate the source for reprint.1. Experimental environment2. Software download3. Start test4. Attached parameter descriptionIn case of accidental deletion or update of data in production, the traditional recovery method is to use backup ...

Introduction to SQL SQL(Structured Query Language) is a set of relational database management system (RDBMS) for management, which is based on ANSI (American National Standards) Institute (American National Organization for Standardization) standard computer language, the more important version is SQL92In addition to supporting standard SQL, a ...

1. Query 1.select * from user #Check all fields 2.select name from user # Query specified fields 2. Query and de duplication #Query name and remove duplicate select distinct name from user 3. Query with conditions #Query the information named Tom select * from user where name="Tom" 4. Multi criteria query #The query name is Tom and th ...

ADO.NET data access technology Learning objectives Master the basic methods of C# accessing database Master various methods of database query Focus on understanding and mastering the application of OOP principles in data access ADO.NET component and database connection Understand ADO NET ActiveX Data Objects(ADO) Yes NET platform, a set of o ...

preface This article belongs to the column "1000 problems to solve big data technology system", which is original by the author. Please indicate the source of quotation. Please help point out the deficiencies and errors in the comment area. Thank you! Please refer to table of contents and references for this column 1000 problems ...

LINQ introduction What problems can LINQ solve In the development of NET platform, object-oriented programming language and data access method are separated for a long time. Data access is queried through SQL. This way of embedding SQL statements is very prone to errors. SQL and XML have their own query language, while objects do not have their ...

This article mainly introduces the relevant knowledge of JOIN clause in SQL (Structured Query Language), and introduces the common usage of JOIN through usage examples. Note: the usage example in this article is for MySQL database. 1 OverviewThe JOIN clause in SQL is used to combine rows from two or more tables. In actual database applications, ...

The SQL language provides two different ways to use it interactive Embedded Why introduce embedded SQL SQL language is a non procedural language Transaction processing applications require high-level languages There are differences in details between the two methods. In the programming environment, SQL statements need to be expanded Process of ...