Mysql _ Introduction

Mysql _ as a black box tester for online games, I was told or told about using the database for a long period of time (about one and a half years) after I joined the company (mysql) only three points are required: 1 single table query, select * from table_name; 2 join Table query, select. *, B. * from tablea_name a, tableb_name B where. columnx = B. columnx; 3 unix timestamp Conversion Function, select unix_timestamp (), from_unixtime (); www.2cto.com with the work needs, I have a little work contact with the database administrator, gradually finding that the lack of database knowledge has become a factor affecting work efficiency and communication, so I began to use my spare time to make up for it. On the one hand, the problem encountered on the day was solved quickly to avoid affecting the work progress, and then recorded it, learning related knowledge points after work, on the one hand from the shortest to the deep mysql System learning. To better remember and control the learning progress, the system writes important content in the Word document when learning mysql. The exercises are directly performed on the mysql gui. Therefore, you need to install mysql and mysql gui, in addition, it is possible to create database tables for some exercises. The table structure and data are as practical as possible, because we did a game test. At that time, we created several tables for the exercises following the company's database structure. After a certain understanding of the database, we found that even if there is no working contact with the database administrator, this knowledge is still of great benefit to the improvement of work efficiency and career development. Understand the important database terminology list of mysql: a database is a container that stores organized data (usually a file or a group of files ). It is incorrect that people usually use the database term to represent the database software they use. Specifically, database software should be called a database management system (or DBMS ). Databases are created and manipulated through DBMS. A structured list of a specific type of data in a table www.2cto.com. Schema information about the layout and features of databases and tables. A field in the column table. All tables are composed of one or more columns. It is very important to divide data into multiple columns correctly. The data type allowed by the Data Type (datatype. Each table column has a corresponding data type, which limits (or permits) the data stored in this column. The data type limits the types of data that can be stored in columns. Data Types also help to classify data correctly and play an important role in optimizing disk usage. Therefore, you must pay special attention to the data type when creating a table. Data Type compatibility data types and their names are a major cause of SQL incompatibility. Although most data types are consistent, this is not the case for many more advanced data types. Even worse, we may find that the same data type has different names in different DBMS. There is no way to do this. It is important to remember these differences when creating a table structure. A record in the row table www.2cto.com ). In many cases, the line and record terms can be used in exchange, but technically, the line is the correct term. The value of a primary key column (or a group of columns) uniquely identifies each row in the table. It is difficult to update or delete specific rows in a table without a primary key, because there is no secure method to ensure that only related rows are involved. Any column in the table can be used as the primary key as long as it meets the following conditions: 1) any two rows do not have the same primary key value; 2) each row must have a primary key value (the primary key value cannot be NULL); 3) the value in the primary key column cannot be modified or updated; 4) the primary key value cannot be reused (if a row is deleted, its primary key cannot be assigned to a new row ). Multiple columns can be used together as the primary key. When multiple columns are used as the primary key, the preceding conditions must be applied to all columns that constitute the primary key. The combination of all column values must be unique. Www.2cto.com SQL is short for structured query language. Like any other language, the best way to learn SQL is to practice it on your own. Therefore, a database and an application system used to test SQL statements are required. Author signjing