Quicksort is one of the most common sorting algorithms. The logic of Quicksort is choosing a number (called pivot) and divide the rest into two parts. After first sorting the numbers on the left side are all less than pivot and the numbers on the right side are all bigger than pivot. Then do the same thing for left and right part.
The statement of creating index on table will lock the table.It will cost a long time if you create multiple indexes in a big table. You can use ALTER TABLE ... to create or drop multiple indexes in one sql. The example is here.
If the message No space left on device appears that means you need clear the file on your system or add new disk for your computer. "No space" not only means no free disk, it may also mean there is no iNodes in your system.
MyBatis is a Java persistence framework. It is easy to use and learn. This tutorial shows the most common scenarios.
The first level cache is enabled by default in MyBatis. It will cache the result after querying data from database. The second time you query MyBatis won't hit db. The first level cache is for session. If the session is close the cache will be cleared. I assume that you have created database and insert some data in your table.
In MySQL you can use desc
Swagger can help you generate document for your restful API. This blog will show you how to use it. I assume that you have known how to use Spring Boot. The structure of example project is like following.
Use jsonassert framework to compare two json are same or not. It only compare the content of them. The example code is here;
Use \d or \d+ in psql command to show all tables. \d+ will show additional detail of tables;
The annotation @ResponseBody can help you convert object to json. Sometimes if the field of object is null the json returned like following.
Use set command to list all environment variables. They are like following in my computer.
Use du command to show the size of folder. Before testing this command we will create a directory and a file.
In PosgreSQL there are several ways to switch database.
In PostgreSQL there are two ways to list all databases.
When I start tomcat to deploy my application I got the error message like following.