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Technical Articles

Database

SQL

what is microsoft sql server

Microsoft SQL Server is a comprehensive database platform that provides enterprise-level data management using integrated business intelligence tools; the Microsoft SQL Server database engine provides more secure and reliable storage functions for relational data and structured data.

Feb 18, 2020 am 10:20 AM

sql

Usage of inner join in sql

INNER JOIN is a multi-table connection keyword in SQL. The syntax is: SELECT * FROM table1 INNER JOIN table2 ON table1.field1 compopr table2.field2, which is used to query related data between two tables.

Feb 14, 2020 pm 04:22 PM

sql inner join

What does where 1=1 mean in SQL statement?

Where 1=1 in the SQL statement is automatically generated by the program to avoid grammatical errors caused by the first word after the where keyword being "and".

Feb 13, 2020 pm 05:19 PM

sql where

The principle of SQL injection attack

The principle of SQL injection attack: A malicious user inserts a SQL statement into the request content during the process of submitting a query request. At the same time, the program itself overly trusts the user input content and fails to filter the SQL statement inserted by the malicious user, causing the SQL statement to be directly Server-side execution.

Feb 13, 2020 pm 05:13 PM

sql 注入攻击原理

What is the SQL statement to create a view?

SQL creates a view using the create view statement. The specific usage is as follows: create view viewname as select * from <name of table> where <some restrictions>.

Feb 13, 2020 pm 04:56 PM

sql 创建视图

Usage of case when in sql

Case has two formats: simple case function and case search function. The simple case function is relatively simple to write, but compared with the case search function, there are some functional limitations, such as writing predicates.

Feb 13, 2020 pm 04:35 PM

sql case when 用法

What does 'select 1 from table' mean?

"Select 1 from table" means to check whether there are records in the table. 1 is a constant, and the value of all rows found is it. In terms of efficiency, 1>column>*, because 1 does not need to look up the dictionary table .

Feb 13, 2020 pm 04:13 PM

sql select

How to delete data using sql statement

SQL can use the delete statement to delete data. The syntax is "delete from table name where...". When where does not match any records, no data will be deleted. When the where statement is not written, the table will be deleted. All data.

Feb 07, 2020 pm 01:16 PM

sql 删除数据

sql intercepts the first digits of a string

In SQL, you can use the LEFT function to get the first few digits of a string. The syntax is "LEFT(string,length)", string is the intercepted string, and length is the length to be intercepted, for example, LEFT("www.php. cn",3) can intercept www.

Feb 07, 2020 pm 12:37 PM

sql 截取字符串

Functions of sql language

The functions of SQL language: 1. Data definition function, which can define the three-level schema structure of the database, namely external schema, global schema and internal schema structure; 2. Data manipulation function, including data insertion, deletion and deletion of basic tables and views. Modification; 3. The data control function is mainly to control the user's access rights to ensure the security of the system.

Feb 06, 2020 pm 01:16 PM

sql 功能

sql statement to modify data

SQL uses the update statement to modify data. The syntax format is "update <table name> set field 1 = value where <condition>". When multiple values need to be modified, each value in the set clause can be separated by commas.

Feb 06, 2020 am 11:02 AM

sql 修改数据

SQL fuzzy query statement

The syntax of the sql fuzzy query statement is "SELECT field FROM table WHERE certain field Like condition", among which conditions, SQL provides four matching modes, namely: [%], [_], [[]], [^].

Feb 06, 2020 am 10:50 AM

sql 模糊查询

What is the execution order of sql statements?

Execution order: the from clause assembles data from different data sources; the where clause filters record rows based on specified conditions; the group by clause divides the data into multiple groups; uses aggregate functions for calculations; uses the having clause to filter Group by; evaluate all expressions; select set output, etc.

Jan 07, 2020 pm 03:15 PM

sql语句执行顺序

What is the usage of in in sql

The IN operator allows us to specify multiple values in the WHERE clause. Syntax: SELECT column_name(s), FROM table_name, WHERE column_name IN (value1, value2,...).

Jan 07, 2020 pm 03:02 PM

sql in 用法