Programmer Group

1. Why use Flyway In daily development, the following problems are often encountered: 1. Forget to execute SQL written by yourself in all environments; 2. The SQL written by others cannot be sure whether it has been executed in all environments; 3. Someone has modified the executed SQL and expects to execute it again; 4. It is necessary to a ...

Optimization of 20 SQL statements with twice the result with half the effort 1. Use the where condition to limit the data to be queried to avoid returning redundant rows Suppose the business scenario is to query whether a user is a member Before optimization: List<Long> userIds = sqlMap.queryList("select userId from user where isVip=1 ...

summary on must be used with join SQL1 finds all the information of the latest employee select*from employees order by hire_date desc limit 1; select * from employees where hire_date = (select max(hire_date) from employees); ORDER BY sorts the result set according to the specified column. By default, ORDER BY DESC is in ascending ...

analysis ● 1. Observe and run for at least one day to see the slow production ● 2. Start the slow query log, set the threshold value, for example, slow SQL is more than 5 seconds, and grab it ● 3.explain + slow SQL analysis ● 4.show profile ● 5. Optimize the parameters of SQL database server (O & M or DBA) summary ● 1. Enable and capture ...

1. Add records for SQL tables grammar Insert some columns into the table: insert into student (Column name 1,Column name 2,Column name 3...) values (Value 1, value 2, value 3...); Insert all columns into the table: insert into student values (Value 1, value 2, value 3...); matters needing attention 1. The type of value is ...

introduction Full backup is to back up all data contents. There are a lot of duplicate data in the backup data, and the time of full backup and recovery is very long. The solution to the problem of full backup is to use incremental backup. Incremental backup is to back up the files or contents added or changed since the last backup. 1 ...

catalogue 1, Regular expression 1. Introduction 2. Common matching types 3. Query mode 2, Operator 1. Arithmetic operator 2. Comparison operator 3. Logical operator (Boolean)   4. Bitwise operator   3, Connection query 1. Inner connection 2. Left connection 3. Right connection summary 1, Regular expression 1. Introduc ...

MyBatis framework dynamic Sql Dynamic SQL: judge the conditions through various tags provided by MyBatis to realize dynamic splicing of SQL statements. The expression used for conditional judgment here is OGNL expression. The commonly used dynamic SQL tags are,,, and so on. The dynamic SQL statement of MyBatis is very similar to the stat ...

The structure of the circle of friends really gives me a headache - how to implement it in a multi-layer architecture and how to write the script; And the ghost virtual machine, kind of learning is not good at self castration. Do it from the beginning, then. Each image has its own URL: uniform resource location address protocol: / / hostname [ ...

1. Course introduction first day: 1.Oracle concept and installation 2. Basic query 3. Condition query 4. Functions in Oracle the second day: 1. Multi table query (mysql also has the same concept, different syntax and important aspect) 2. Sub query (it also exists in mysql, with the same concept, different syntax and important aspect) on th ...