MySQL is a relational database management system developed by MySQL AB in Sweden and currently belongs to Oracle. MySQL is one of the most popular relational database management systems. In terms of WEB applications, MySQL is the best RDBMS application software. MySQL is a relational database management system that stores data in different tables rather than putting all the data in one large warehouse, which increases speed and flexibility. The SQL language used by MySQL is the most commonly used standardized language for accessing databases. MySQL software adopts a dual authorization policy and is divided into community version and commercial version. Due to its small size, fast speed, low overall cost of ownership, especially open source, MySQL is generally chosen as the website database for the development of small and medium-sized websites. Due to the excellent performance of its community edition, it can be used with PHP and Apache to form a good development environment.
1. Introduction to mysql 8.0 functions
- limit
If there is an unequal sign (WHERE color!=) in the query condition of the WHERE clause, MySQL will not be able to use indexes. Similarly, if the query condition in the WHERE clause uses the function (WHERE DAY (column)=), MySQL will not be able to use the index. In JOIN operations (when data needs to be extracted from multiple data tables), MySQL can use indexes only if the primary key and foreign key have the same data type. If the comparison operators LIKE and REGEXP are used in the query conditions of the WHERE clause, MySQL can use the index only if the first character of the search template is not a wildcard. For example, if the query criterion is LIKE 'abc%', MySQL will use the index; if the query criterion is LIKE '%abc', MySQL will not use the index. In the ORDER BY operation, MySQL uses an index only if the sorting condition is not a query condition expression. (Still, in queries involving multiple data tables, even if indexes were available, those indexes would do little to speed up ORDER BY.) If a data column contains many duplicate values, even if it is indexed, it will not work well. For example, if a data column contains net values such as "0/1" or "Y/N", there is no need to create an index for it. In theory, it is entirely possible to create an index for each field in the data table, but MySQL limits the total number of indexes in the same data table to 16.
- Index of InnoDB data table
Compared with InnoDB tables, on InnoDB tables, indexes are much more important to InnoDB tables. On InnoDB data tables, indexes not only play a role when searching for data records, but are also the basis of the row-level locking mechanism. "Data row-level locking" means locking individual records being processed during the execution of a transaction and preventing access by other users. This locking affects (but is not limited to) the SELECT, LOCKINSHAREMODE, SELECT, FORUPDATE commands, and the INSERT, UPDATE, and DELETE commands. For efficiency reasons, row-level locking of InnoDB data tables actually occurs on their indexes, not on the data tables themselves. Obviously, the row-level locking mechanism can only be effective if the relevant data table has a suitable index to lock.
2. Streamlined explanation
Except for the mysql main service, other redundant services and extension components, as well as pdb files, have been streamlined, thereby reducing the size to more than 200 MB. After compression, it is only 13. It is suitable for personal learning and users who have no other additional needs.
3. instructions for use
After downloading and extracting it to the specified directory, the following files are obtained:
There are three scripts:
- startCome.bat: Start the mysql server directly
- install.bat: Install mysql as a Windows service
- uninstall.bat: Uninstall the mysql service
User name: root, password is empty
4. download address
https://ldqk.lanzouy.com/iooMWz1w5pi
For more information, please click the link below to visit the official website of diligent and lazy people, especially when the link in the article fails, haha.