Data knowledge base and query collection skills in MySQL

MySQL is an open source relational database management system that is widely used in various applications. One of my technical jobs is to manage MySQL databases. What I want to share in this article is how to create and manage the data knowledge base in MySQL, as well as some collection techniques that may be used when querying data.

1. Data knowledge base

In MySQL, the data knowledge base is a logical container used to store tables, views and other objects. A MySQL server can contain multiple data repositories, each with a unique name. Here is some useful information about data repositories:

1. Creating a data repository

To create a new data repository, enter the following command in command line mode ：

CREATE DATABASE ;

For example, to create a data knowledge base named "mydb", you can use the following command:

CREATE DATABASE mydb;

2. Using a data repository

Use the following command to select a data repository in MySQL:

USE ;

For example, use the following command to select the data repository named "mydb":

USE mydb;

3. Delete the data repository

To To delete a data repository, you can use the following command:

DROP DATABASE ;

Please note that deleting a data repository will permanently delete all tables, views, and other objects in it. Please proceed with caution.

2. Query collection skills

In MySQL, there are many useful query skills that can save time and improve efficiency. Here are some techniques I like to use:

1. List all data repositories

Use the following command to list all data repositories in MySQL:

SHOW DATABASES;

2. List all tables in the data repository

To list all tables in the current data repository, use the following command:

SHOW TABLES;

If you want to list all tables in other data repositories, use the USE command to select that data repository before using the SHOW TABLES command.

3. Show table details

To view the structure and other details of a table, use the following command:

DESCRIBE ;

For example, to view the details of a table named "customers", use the following command:

DESCRIBE customers;

4. Select specific rows and columns

Sometimes you just need to select specific rows and columns in a table. Here are some common query examples:

Select the first 10 rows:

SELECT * FROM LIMIT 10;

Select specific columns:

SELECT , , ... FROM ;

For example, to select only the "first_name" and "last_name" columns in the "customers" table, use the following Command:

SELECT first_name, last_name FROM customers;

5. Use WHERE clause to filter data

Use WHERE clause to filter the table according to specific conditions The data. Here are some examples:

Filter records with the last name "Smith" in the "customers" table:

SELECT * FROM customers WHERE last_name = 'Smith';

Filter" orders" table only contains order records with a specific date (such as "2021-07-01"):

SELECT * FROM orders WHERE order_date = '2021-07-01';

6. Sort by conditions

Use the ORDER BY clause to sort the query results in ascending or descending order. Here are some common query examples:

Sort the "customers" table alphabetically by last name:

SELECT * FROM customers ORDER BY last_name;

Descending order by order date Sorting the "orders" table:

SELECT * FROM orders ORDER BY order_date DESC;

These are just some tips and favorites in MySQL queries, there are of course many other useful commands and clauses. As with any technology, the best approach is by trying different methods and seeing which one works best for your needs.

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