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Technical Articles

Database

SQL

A flip-flop has several steady states

The flip-flop has two stable states, which can represent binary numbers 0 and 1 respectively. It can maintain the stable state without external trigger; under external trigger, the two stable states can be converted into each other, and the converted stable state can be maintained for a long time. This is Enables flip-flops to memorize binary information and is often used as a binary storage unit.

Jan 28, 2021 pm 06:11 PM

触发器

How to set foreign keys in database sql statement

Methods for setting foreign keys in database SQL statements: 1. Add foreign key constraints [alter table add foreign key (foreign key field) references from table main table (primary key field)]; 2. Delete foreign key constraints [alter table table name drop foreig 】.

Jan 26, 2021 pm 03:39 PM

数据库sql 外键

What type of database management system is sql?

SQL, the full name of SQL Server, is a relational database management system. The SQL Server database engine provides more secure and reliable storage capabilities for relational and structured data, allowing you to build and manage highly available and high-performance data applications for your business.

Jan 22, 2021 pm 01:45 PM

sql SQL Server 数据库管理系统

Understand inner joins, left outer joins, and right outer joins of sql statements

When you first learn databases, do you have some doubts about the connection query in DQL? Do you know when and what kind of connection query should be used in what scenario? Don't worry, let me introduce to you the understanding of the characteristics and application scenarios of inner joins, left outer joins, and right outer joins in the SQL tutorial column for your reference.

Jan 15, 2021 am 10:20 AM

左连接特点

Troubleshooting SQL injection issues

What is SQL injection? Take a look at the definition of Baidu Encyclopedia. The following SQL tutorial uses an example to explain what SQL injection is: Create a new database, create a table, and add two rows of data: use db1;create table user(id int...

Jan 12, 2021 am 09:22 AM

SQL注入

SQL optimization minimalist rules that you must not know

SQL Tutorial As the standard language of relational database, it is one of the essential skills for IT practitioners. SQL itself is not difficult to learn, and writing query statements is also very easy, but it is difficult to write query statements that can run efficiently.

Jan 02, 2021 am 11:23 AM

sql 数据库优化法则

Introducing ten steps to fully understand SQL

Many programmers view SQL as a scourge. SQL is one of the few declarative languages that operates completely differently from the command line languages, object-oriented programming languages, and even functional languages we are familiar with (although some people think that the SQL language is also a functional language ).

Dec 29, 2020 pm 05:57 PM

sql 数据库后端运维程序员

Solving SQL problems will definitely take your understanding of MySQL one step further!

The structure of the attribute table (product_props) introduced in the SQL tutorial column is as follows. Data volume is more than 800W. Field name type description id int id pn_id int attribute type pv_id int attribute value product_id int product ID.

Dec 26, 2020 pm 05:42 PM

MySQL SQL

Record slow SQL optimization practice

Introduction to sql tutorial After optimizing sql slow query, we found the following types of problems in our system: 1. No index built: no index built for the entire table; 2. Index miss: there is an index, but the index is under some query conditions Missed; 3. Searched for additional non-essential fields, resulting in table return; 4. Sorting, aggregation...

Dec 25, 2020 pm 05:23 PM

MySQL SQL

What are the sql query statements?

SQL query statement: 1. View the table structure [SQL>DESC emp]; 2. Query all columns [SQL>SELECT * FROM emp]; 3. Query the specified columns; 4. Query the specified rows; 5. Use arithmetic expressions; 6 , use logical operation symbols.

Dec 10, 2020 pm 02:48 PM

sql查询语句

Learn MyBatis dynamic SQL

SQL tutorial introduces dynamic SQL. One of the powerful features of MyBatis is its dynamic SQL. If you have experience using JDBC or other similar frameworks, you will understand the pain of splicing SQL statements based on different conditions. For example, when splicing, make sure you don't forget to add necessary spaces.

Dec 09, 2020 pm 05:46 PM

mybatis SQL