search
HomeDatabaseMysql TutorialA large collection of MySQL sql basic statements

I am accustomed to using SQL Sever to directly design the database every time, but do not pay enough attention to SQL statements. I took the opportunity of this reconstruction of the computer room cooperation version to use SQL statements to design the database and at the same time Let’s sort out the basic usage of SQL statements.

【Classification】

There are 9 types of SQL statements, which can be roughly divided into 4 types according to their functions:

1. Query statement: select ----The most commonly used statement in the database

2. Data definition: create, drop, alter----for Operations on databases, data tables, and fields in tables

3. Data manipulation: insert, update, delete----the legendary "add, delete, modify, query", for specific Data operations

4. Data control: grant, revoke----definition and deletion of permissions

[Statement summary]

1. Create a database

##

create database RechargeSystem
on primary    --主文件组
(
	/*数据文件的具体描述*/
	name='RechargeSystem_data',  --主数据文件的逻辑名称
	filename='G:\RechargeSystem\RechargeSystem_data.mdf',  --主数据文件的物理名称
	size=5mb,       --初始大小
	maxsize=100mb,  --增长最大值
	filegrowth=15%   --主数据文件增长率
)
log on
(
	/*日志文件的具体描述*/
	name='RechargeSystem_log',
	filename='G:\RechargeSystem\RechargeSystem_log.ldf',
	size=2mb,
	filegrowth=1mb
)

If you have learned the operating system, you will not be very familiar with these definition statements. Strangely enough, a database group file is also a kind of file and needs to have a logical name (i.e. file name), physical name (actual storage address on the disk), file size, etc.; the log file records all logical operations in the database, with details such as advantages and disadvantages. For the content, see Baidu Encyclopedia: Log file


2. Basic table operations

--------------------------------------------------------------------------------------------------------------------------------------------
       create table <基本表名>   ---建立表格
               (<列名 类型 not null>,
                 primary key(列名,列名),--主键约束
                 foreign key (<列名>) references tableName(<列名>),--外键约束);
--------------------------------------------------------------------------------------------------------------------------------------------
      alter table <表名> add <列名><数据类型>  --添加列

You can set the primary and foreign keys of the established table:
##

  alter table <表名> add primary key(<列名>,<列名>)
      alter table<表名> add foreign key(<列名>) references tableName(<列名>)

Delete a column: alter table drop [cascade|restrict] --restrict will Views and constraints are also sectored


---------------------- -------------------------------------------------- -------------------------------------------------- ------------------

## drop table

[cascade|restrict] --Delete table, with constraints Restrict

must be added to the condition

3. Query statement:

Regular The query statement is: select * from datatable


It should be noted that nested and connected queries are queried from multiple tables. This combination relationship is commonly used in M:N relationships. Find the corresponding relationship.

 select TB1.column1,TB1.column2
                from TB1
                where TB1.column1 in(select column1
                                                         from TB2
                                                        where TB2.column2="特定值");


This relationship is not recommended for users with confusing logic, as it is particularly likely to cause search failure.

---------------------------------------- -------------------------------------------------- -------------------------------------------------- --

In addition, the SQL query statement also provides basic aggregate functions for easy query use:

count(*) --- --------------------Calculate the number of tuples, that is, how many columns there are in total

count()----------------Calculation of the number of values ​​in a column

sum()-- ------------------The sum of a column of values ​​(numeric type)

avg ()-- -------------Average (must be numeric type)

max()-------- ---------Maximum value

## min()------------------ ----Minimum value

#--------------------------------------------- -------------------------------------------------- --------------------------------------------------

Complete semantic structure:

                                                                                                                                                                 ’’’''‐‐' '' #''''''''‐'‐'‐'‐‐‐‐---- where

## group by ----------------------- ---------Grouping based on a certain field

## Having -------------- ------Information that does not meet the group conditions is filtered out

## Order by ---------- --------Asc ascending order, desc descending order

----------------------- -------------------------------------------------- -------------------------------------------------- -------------------

## Special query requirements:

1. Comparison Operations: ,>=,!=

## 2. Matching operation: %---matches characters consisting of zero or more characters , "_" single character matches

3. Null value is Null

4. Aggregated resource comparison: in, some, any, all

5. Whether the set is non-empty: exits --- If it is not empty, it is true, otherwise it is false

6. Whether there are duplicates in the set Tuple: unique--------repeat to true, otherwise false

-------------------------- -------------------------------------------------- -------------------------------------------------- -----------------------

4. Data operation statements

Insert: insert into

(, ...) values('value', 'value')

Delete: delete from

where condition

Modify: update

set ##5. Embedded SQL usage technology, commonly used execution views, stored procedures, etc., add exec to execute

[Summary]

Knowledge is always like this , you will gain different results every time you study, especially after using it, you will try to compare the differences between different methods. I look forward to the next comparative study of database views, stored procedures and security settings.

The above is the content of a large collection of MySQL sql basic statements. For more related content, please pay attention to the PHP Chinese website (www.php.cn)!

Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
Explain the role of InnoDB redo logs and undo logs.Explain the role of InnoDB redo logs and undo logs.Apr 15, 2025 am 12:16 AM

InnoDB uses redologs and undologs to ensure data consistency and reliability. 1.redologs record data page modification to ensure crash recovery and transaction persistence. 2.undologs records the original data value and supports transaction rollback and MVCC.

What are the key metrics to look for in an EXPLAIN output (type, key, rows, Extra)?What are the key metrics to look for in an EXPLAIN output (type, key, rows, Extra)?Apr 15, 2025 am 12:15 AM

Key metrics for EXPLAIN commands include type, key, rows, and Extra. 1) The type reflects the access type of the query. The higher the value, the higher the efficiency, such as const is better than ALL. 2) The key displays the index used, and NULL indicates no index. 3) rows estimates the number of scanned rows, affecting query performance. 4) Extra provides additional information, such as Usingfilesort prompts that it needs to be optimized.

What is the Using temporary status in EXPLAIN and how to avoid it?What is the Using temporary status in EXPLAIN and how to avoid it?Apr 15, 2025 am 12:14 AM

Usingtemporary indicates that the need to create temporary tables in MySQL queries, which are commonly found in ORDERBY using DISTINCT, GROUPBY, or non-indexed columns. You can avoid the occurrence of indexes and rewrite queries and improve query performance. Specifically, when Usingtemporary appears in EXPLAIN output, it means that MySQL needs to create temporary tables to handle queries. This usually occurs when: 1) deduplication or grouping when using DISTINCT or GROUPBY; 2) sort when ORDERBY contains non-index columns; 3) use complex subquery or join operations. Optimization methods include: 1) ORDERBY and GROUPB

Describe the different SQL transaction isolation levels (Read Uncommitted, Read Committed, Repeatable Read, Serializable) and their implications in MySQL/InnoDB.Describe the different SQL transaction isolation levels (Read Uncommitted, Read Committed, Repeatable Read, Serializable) and their implications in MySQL/InnoDB.Apr 15, 2025 am 12:11 AM

MySQL/InnoDB supports four transaction isolation levels: ReadUncommitted, ReadCommitted, RepeatableRead and Serializable. 1.ReadUncommitted allows reading of uncommitted data, which may cause dirty reading. 2. ReadCommitted avoids dirty reading, but non-repeatable reading may occur. 3.RepeatableRead is the default level, avoiding dirty reading and non-repeatable reading, but phantom reading may occur. 4. Serializable avoids all concurrency problems but reduces concurrency. Choosing the appropriate isolation level requires balancing data consistency and performance requirements.

MySQL vs. Other Databases: Comparing the OptionsMySQL vs. Other Databases: Comparing the OptionsApr 15, 2025 am 12:08 AM

MySQL is suitable for web applications and content management systems and is popular for its open source, high performance and ease of use. 1) Compared with PostgreSQL, MySQL performs better in simple queries and high concurrent read operations. 2) Compared with Oracle, MySQL is more popular among small and medium-sized enterprises because of its open source and low cost. 3) Compared with Microsoft SQL Server, MySQL is more suitable for cross-platform applications. 4) Unlike MongoDB, MySQL is more suitable for structured data and transaction processing.

How does MySQL index cardinality affect query performance?How does MySQL index cardinality affect query performance?Apr 14, 2025 am 12:18 AM

MySQL index cardinality has a significant impact on query performance: 1. High cardinality index can more effectively narrow the data range and improve query efficiency; 2. Low cardinality index may lead to full table scanning and reduce query performance; 3. In joint index, high cardinality sequences should be placed in front to optimize query.

MySQL: Resources and Tutorials for New UsersMySQL: Resources and Tutorials for New UsersApr 14, 2025 am 12:16 AM

The MySQL learning path includes basic knowledge, core concepts, usage examples, and optimization techniques. 1) Understand basic concepts such as tables, rows, columns, and SQL queries. 2) Learn the definition, working principles and advantages of MySQL. 3) Master basic CRUD operations and advanced usage, such as indexes and stored procedures. 4) Familiar with common error debugging and performance optimization suggestions, such as rational use of indexes and optimization queries. Through these steps, you will have a full grasp of the use and optimization of MySQL.

Real-World MySQL: Examples and Use CasesReal-World MySQL: Examples and Use CasesApr 14, 2025 am 12:15 AM

MySQL's real-world applications include basic database design and complex query optimization. 1) Basic usage: used to store and manage user data, such as inserting, querying, updating and deleting user information. 2) Advanced usage: Handle complex business logic, such as order and inventory management of e-commerce platforms. 3) Performance optimization: Improve performance by rationally using indexes, partition tables and query caches.

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
4 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
R.E.P.O. Best Graphic Settings
4 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
R.E.P.O. How to Fix Audio if You Can't Hear Anyone
4 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
WWE 2K25: How To Unlock Everything In MyRise
1 months agoBy尊渡假赌尊渡假赌尊渡假赌

Hot Tools

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

SecLists

SecLists

SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.

Dreamweaver Mac version

Dreamweaver Mac version

Visual web development tools

PhpStorm Mac version

PhpStorm Mac version

The latest (2018.2.1) professional PHP integrated development tool