查询数据库 英文命令是什么

查询数据库的英文命令是SQL（Structured Query Language），即结构化查询语言。SQL语言包括数据操作语言、数据定义语言、数据控制语言、事务控制语言。这些语言可以完成数据查询、插入、更新和删除，以及创建、更改和删除表和视图等操作。其中，数据操作语言（Data Manipulation Language, DML）是最常用的一种，它包括SELECT、INSERT、UPDATE和DELETE等命令，用于对数据库进行查询和修改。例如，如果我们想查询数据库中的所有数据，可以使用SELECT * FROM table_name的命令。

一、DATA MANIPULATION LANGUAGE (DML)

Data Manipulation Language (DML) 是用于检索、存储、修改、删除、插入和更新数据的SQL组件。这些命令是SQL语言的基础，使用它们可以有效地管理数据库中的数据。

SELECT是最常用的DML命令，它可以从一个或多个表中检索数据。例如，SELECT * FROM Employees会返回Employees表中的所有数据。

INSERT命令用于向表中插入新的行。例如，INSERT INTO Employees (FirstName, LastName, Age) VALUES ('John', 'Doe', 30)会在Employees表中插入一行新数据。

UPDATE命令可以修改表中的数据。例如，UPDATE Employees SET Age = 31 WHERE FirstName = 'John' AND LastName = 'Doe'会将名为John Doe的员工的年龄更新为31。

DELETE命令可以从表中删除行。例如，DELETE FROM Employees WHERE FirstName = 'John' AND LastName = 'Doe'会删除名为John Doe的员工的数据。

二、DATA DEFINITION LANGUAGE (DDL)

Data Definition Language (DDL) 是用于创建、修改和删除数据库对象（如表、视图和索引）的SQL组件。

CREATE命令用于创建新的数据库、表、视图或其他对象。例如，CREATE TABLE Employees (FirstName VARCHAR(20), LastName VARCHAR(20), Age INT)会创建一个新的Employees表。

ALTER命令用于修改现有的数据库对象。例如，ALTER TABLE Employees ADD Email VARCHAR(50)会在Employees表中添加一个新的Email列。

DROP命令用于删除现有的数据库、表、视图或其他对象。例如，DROP TABLE Employees会删除Employees表。

三、DATA CONTROL LANGUAGE (DCL)

Data Control Language (DCL) 是用于控制对数据库的访问的SQL组件。

GRANT命令用于给用户授权，例如，GRANT SELECT, INSERT, UPDATE ON Employees TO John会给John对Employees表的查询、插入和更新权限。

REVOKE命令用于撤销用户的权限。例如，REVOKE SELECT, INSERT, UPDATE ON Employees FROM John会撤销John对Employees表的查询、插入和更新权限。

四、TRANSACTION CONTROL LANGUAGE (TCL)

Transaction Control Language (TCL) 是用于管理数据库中的事务的SQL组件。

COMMIT命令用于将事务的修改永久保存到数据库。例如，如果您对Employees表进行了一些更改，并且希望这些更改永久保存，那么可以使用COMMIT命令。

ROLLBACK命令用于撤销未提交的事务。例如，如果您对Employees表进行了一些更改，但现在希望撤销这些更改，那么可以使用ROLLBACK命令。

SAVEPOINT命令用于在事务中创建一个恢复点，以便在事务失败时可以回滚到该点。例如，SAVEPOINT savepoint1会创建一个名为savepoint1的恢复点。如果事务失败，您可以使用ROLLBACK TO savepoint1命令回滚到该点。

总的来说，SQL提供了一种简单有效的方法来查询和操作数据库。通过使用这些命令，我们可以轻松地管理数据库中的数据，创建和修改数据库结构，控制对数据库的访问，以及管理数据库事务。

相关问答FAQs：

1. What is the English command for querying a database?

The English command for querying a database is "SELECT". SELECT is used to retrieve data from one or more tables in a database. It allows you to specify the columns you want to retrieve, the table(s) you want to query, and any conditions or filters you want to apply to the data.

For example, if you have a database table called "customers" with columns such as "name", "email", and "phone", you can use the SELECT command to retrieve all the customer names and emails with the following query:

SELECT name, email FROM customers;

This command will return a result set containing the names and emails of all the customers in the table.

2. How can I query a database using an English command?

To query a database using an English command, you need to use a database management system (DBMS) that supports the SQL (Structured Query Language) syntax. SQL is a standard language for interacting with databases.

First, you need to open a connection to the database using the appropriate driver or connector for your programming language or tool. Once the connection is established, you can execute SQL statements, including the SELECT command, to retrieve data from the database.

For example, if you are using Python and the MySQL database, you can use the "mysql-connector-python" library to connect to the database and execute SQL queries. Here is an example code snippet:

import mysql.connector

# Open a connection to the database
cnx = mysql.connector.connect(
    host="localhost",
    user="username",
    password="password",
    database="database_name"
)

# Create a cursor object to execute SQL queries
cursor = cnx.cursor()

# Execute a SELECT query
query = "SELECT name, email FROM customers"
cursor.execute(query)

# Fetch all the rows from the result set
result_set = cursor.fetchall()

# Process the result set
for row in result_set:
    name = row[0]
    email = row[1]
    print(name, email)

# Close the cursor and the connection
cursor.close()
cnx.close()

This code connects to a MySQL database, executes a SELECT query to retrieve the names and emails of all the customers, and then processes and prints the result set.

3. Are there any other English commands besides SELECT for querying a database?

Yes, besides the SELECT command, there are several other English commands that can be used for querying a database. Some of the commonly used ones are:

• INSERT: Used to insert new data into a table.
• UPDATE: Used to update existing data in a table.
• DELETE: Used to delete data from a table.
• CREATE: Used to create a new table, view, or other database objects.
• ALTER: Used to modify the structure of a table or other database objects.
• DROP: Used to delete a table, view, or other database objects.
• GRANT: Used to grant privileges or permissions to users or roles.
• REVOKE: Used to revoke privileges or permissions from users or roles.

These commands, along with the SELECT command, form the core set of SQL commands for interacting with a database. Each command has its own syntax and usage, and they can be combined and nested to perform more complex database operations.