国产av日韩一区二区三区精品,成人性爱视频在线观看,国产,欧美,日韩,一区,www.成色av久久成人,2222eeee成人天堂

Home Database Mysql Tutorial What does sql mean?

What does sql mean?

May 06, 2019 pm 04:30 PM
sql

The full name of sql is Structured Query Language, which is a special-purpose programming language. It is a database query and programming language used to access data, query, update and manage relationships. The database system is also the extension of the database script file.

What does sql mean?

SQL is a high-level non-procedural programming language that allows users to work on high-level data structures. It does not require users to specify the data storage method, nor does it require users to understand the specific data storage method, so different database systems with completely different underlying structures can use the same structured query language as the interface for data input and management. Structured Query Language statements can be nested, which makes it extremely flexible and powerful.

Structured Query Language SQL contains 6 parts:

1. Data Query Language (DQL: Data Query Language):

its statements, Also called a "data retrieval statement", it is used to obtain data from a table and determine how the data is presented in the application. The reserved word SELECT is the most commonly used verb in DQL (and all SQL). Other commonly used reserved words in DQL include WHERE, ORDER BY, GROUP BY and HAVING. These DQL reserved words are often used with other types of SQL statements.

2. Data Manipulation Language (DML):

Its statements include the verbs INSERT, UPDATE and DELETE. They are used to add, modify and delete rows in the table respectively. Also known as Action Query Language.

3. Transaction Processing Language (TPL):

Its statements can ensure that all rows of the table affected by the DML statement are updated in a timely manner. TPL statements include BEGIN TRANSACTION, COMMIT and ROLLBACK.

4. Data Control Language (DCL):

Its statements obtain permission through GRANT or REVOKE to determine the access of individual users and user groups to database objects. Some RDBMS can use GRANT or REVOKE to control access to individual columns of a table.

5. Data Definition Language (DDL):

Its statements include the verbs CREATE and DROP. Create a new table or delete a table (CREAT TABLE or DROP TABLE) in the database; add indexes to the table, etc. DDL includes many reserved words related to obtaining data in human database directories. It is also part of the action query.

6. Pointer Control Language (CCL):

Its statements, such as DECLARE CURSOR, FETCH INTO and UPDATE WHERE CURRENT, are used to operate on individual rows of one or more tables.

The above is the detailed content of What does sql mean?. For more information, please follow other related articles on the PHP Chinese website!

Statement of this Website
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

Hot AI Tools

Undress AI Tool

Undress AI Tool

Undress images for free

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.

Clothoff.io

Clothoff.io

AI clothes remover

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

Hot Topics

PHP Tutorial
1502
276
MySQL: A Practical Application of SQL MySQL: A Practical Application of SQL May 08, 2025 am 12:12 AM

MySQL is popular because of its excellent performance and ease of use and maintenance. 1. Create database and tables: Use the CREATEDATABASE and CREATETABLE commands. 2. Insert and query data: operate data through INSERTINTO and SELECT statements. 3. Optimize query: Use indexes and EXPLAIN statements to improve performance.

Comparing SQL and MySQL: Syntax and Features Comparing SQL and MySQL: Syntax and Features May 07, 2025 am 12:11 AM

The difference and connection between SQL and MySQL are as follows: 1.SQL is a standard language used to manage relational databases, and MySQL is a database management system based on SQL. 2.SQL provides basic CRUD operations, and MySQL adds stored procedures, triggers and other functions on this basis. 3. SQL syntax standardization, MySQL has been improved in some places, such as LIMIT used to limit the number of returned rows. 4. In the usage example, the query syntax of SQL and MySQL is slightly different, and the JOIN and GROUPBY of MySQL are more intuitive. 5. Common errors include syntax errors and performance issues. MySQL's EXPLAIN command can be used for debugging and optimizing queries.

Where to start writing SQL code? How to start writing SQL code? Guide to starting point of writing SQL code? Where to start writing SQL code? How to start writing SQL code? Guide to starting point of writing SQL code? Jun 04, 2025 pm 07:27 PM

The starting point of writing SQL code is to clarify the requirements. 1) Understand the problem you want to solve and determine the relationship between the required data and tables. 2) Start designing queries from simple SELECT statements and gradually increase complexity. 3) Use visualization tools to understand table structure and consider using JOIN when queries are complex. 4) Test the query and use the EXPLAIN command to optimize performance to avoid common pitfalls such as NULL value processing and inappropriate index use.

SQL's Versatility: From Simple Queries to Complex Operations SQL's Versatility: From Simple Queries to Complex Operations May 05, 2025 am 12:03 AM

The diversity and power of SQL make it a powerful tool for data processing. 1. The basic usage of SQL includes data query, insertion, update and deletion. 2. Advanced usage covers multi-table joins, subqueries, and window functions. 3. Common errors include syntax, logic and performance issues, which can be debugged by gradually simplifying queries and using EXPLAIN commands. 4. Performance optimization tips include using indexes, avoiding SELECT* and optimizing JOIN operations.

How Can I Use Regular Expressions for More Powerful Pattern Matching in SQL? How Can I Use Regular Expressions for More Powerful Pattern Matching in SQL? May 27, 2025 am 12:02 AM

You can use regular expressions in SQL for more powerful pattern matching, by following steps: 1) use REGEXP or REGEXP_LIKE functions for pattern matching and data validation; 2) ensure optimized performance, especially when dealing with large data sets; 3) record and simplify complex patterns for improved maintainability. The application of regular expressions in SQL can significantly enhance data analysis and manipulation capabilities, but attention should be paid to performance and pattern complexity.

SQL and Data Analysis: Extracting Insights from Information SQL and Data Analysis: Extracting Insights from Information May 04, 2025 am 12:10 AM

The core role of SQL in data analysis is to extract valuable information from the database through query statements. 1) Basic usage: Use GROUPBY and SUM functions to calculate the total order amount for each customer. 2) Advanced usage: Use CTE and subqueries to find the product with the highest sales per month. 3) Common errors: syntax errors, logic errors and performance problems. 4) Performance optimization: Use indexes, avoid SELECT* and optimize JOIN operations. Through these tips and practices, SQL can help us extract insights from our data and ensure queries are efficient and easy to maintain.

Beyond the Interface: phpMyAdmin and the Power of SQL Beyond the Interface: phpMyAdmin and the Power of SQL May 02, 2025 am 12:21 AM

The combination of phpMyAdmin and SQL allows users to directly enter and execute SQL commands, implementing more complex queries and database management. 1) In phpMyAdmin, you can execute SQL commands, such as SELECTFROMusersWHEREage>30; 2) Use the EXPLAIN command to analyze the execution plan of the query and optimize performance; 3) By creating indexes, avoiding SELECT and using LIMIT, the query efficiency can be significantly improved.

The Role of SQL in phpMyAdmin: A Deep Dive The Role of SQL in phpMyAdmin: A Deep Dive May 03, 2025 am 12:07 AM

SQL's role in phpMyAdmin is multifaceted, including data operation, database design, optimization and maintenance. 1.SQL is used for basic data operations, such as querying and inserting data. 2.SQL supports complex queries, view creation and stored procedure writing. 3. In phpMyAdmin, SQL commands are executed through the MySQL server, and the results are displayed in a table form. 4. Users can perform performance optimization through SQL, such as indexing and query optimization.

See all articles