Tag:Query statement

  • Explain the execution process of MySQL query statements in detail


    First, simply describe what MySQL has done behind a query statement: The client sends a query to the server. The server first checks the query cache. If the cache is hit, it immediately returns the results stored in the cache. Otherwise, proceed to the next stage. The server side performs SQL parsing and preprocessing, and […]

  • The mybatis query statement returns operations on objects and generic collections


    Mybatis query statements return objects and generic collections Empmapper mapping interface: package cn.et.mybatis.lesson03; import java.util.List; import org.apache.ibatis.annotations.Result; import org.apache.ibatis.annotations.Results; import org.apache.ibatis.annotations.Select; public interface EmpMapper { /** *Query a single piece of data, *The column name of each column will match the corresponding attribute in the EMP entity class *When matching, both sides will be turned […]

  • Three strategies for rewriting query statements in MySQL


    When optimizing problematic queries, we need to change the way to get the query results – but this does not mean getting the same result set from mysql. Sometimes we can convert a query to a query that gets the same results but has better performance. However, we also need to consider rewriting the query […]

  • Simple operation example of MySQL query statement


    This paper describes the simple operation of MySQL query statements. For your reference, the details are as follows: query Create database and data table –Create database create database python_test_1 charset=utf8; –Using databases use python_test_1; –Students table create table students( id int unsigned primary key auto_increment not null, name varchar(20) default ”, age tinyint unsigned default […]

  • A collection of SQL server query statements


    1、 Simple queryA simple transact SQL query includes only the select list, from clause, and where clause. They respectively describe the columns to be queried and theTables or views, search criteria, and so on. For example, the following statement queries the nickname field and email field with the name “Zhang San” in the testable table. […]

  • Explain SQL Server simple query statement in detail


    Preface For a large number of articles in the principle article Park, especially about index, I also spend a lot of time to learn, which is very helpful for understanding the index principle for the subsequent understanding of query plan and performance tuning, but we just summarize and summarize some contents. In this section, we […]