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Mybatis learning - dynamic SQL What is dynamic SQL Dynamic SQL is to generate different SQL statements according to different conditions Dynamic SQL is similar to JSTL or any text processor based on XML like languages. In previous versions of MyBatis, it took time to understand a large number of elements. With the powerful expression base ...

catalogue 1, Three paradigms of database 1. First paradigm (ensure that each column remains atomic) 2. Second normal form (ensure that every column in the table is related to the primary key) 3. The third paradigm (ensure that each column is directly related to the primary key column, not indirectly) 2, Tablespace 1. Relationship with c ...

Addition, deletion and modification SQL1 insert record (I) In fact, through the output, we can know the value of the inserted data. insert into exam_record values ( null, 1001, 9001, '2021-09-01 22:11:12', '2021-09-01 23:01:12', 90 ), ( null, 1002, 9002, '2021-09-04 07:01:02', null, null ); You can also use interval to ad ...

catalogue object Problem set: --01 list the names of all departments with at least 3 employees --02 list all employees whose salary is more than 'SMITH'. A sub query is used here (that is, the sub query of SMITH's salary) --03 list the names of all employees and their immediate supervisors --04 list employees whose employment date is earl ...

Chapter 7 single line function 1. Understanding of function 1.1 what is a function Function runs through the use of computer language. What is the role of function? It can encapsulate the code we often use and call it directly when necessary. This not only improves the code efficiency, but also improves the maintainability. In SQL, we can al ...

Experimental questions Basic Operation of Experiment 3 Database (1) Create a database textbook: CREATE database textbook (2) Display and modify the maximum number of connections show variables like "max_connections"; set global max connections = 8; (3) Delete the database textbook drop database textbook Experiment 4 Definition and Mo ...

1, The difference between ${} and #{} in MyBatis 1.1 ${} and #{} presentations Database data: dao interface: List<User> findByUsername(String username); List<User> findByUsername2(String username); Mapper.xml: <!-- use#{} --> <select id="findByUsername" parameterType="java.lang.String" resultType="com.lscl.entity ...

background MySQL has become the first choice for most companies with low-cost and rich Internet resources. Although the performance is excellent, how to better use the so-called "good horse with good saddle" has become a compulsory course for development engineers. We often see requirements such as "proficient in MySQL", &q ...

JDBC overview Basic introduction Simulate JDBC public class TestJdbc { public static void main(String[] args) { JdbcInterface jdbcInterface = new MysqlJdbcImpl(); //Complete the operation of mysql jdbcInterface.getConnection(); jdbcInterface.crud(); jdbcInterface.close(); } } //jdbc interfa ...

Connection query (this article only introduces the connection query of SQL 92 standard in detail) 1, Meaning and classification of connection query meaning: Also known as multi table query, join query will be used when the query fields come from multiple tables Cartesian product phenomenon: Suppose that table 1 has m rows, table 2 has n ...