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Technical Articles

Database

SQL

What problems may arise from concurrent database operations?

The quality of the concurrency control mechanism is one of the important indicators of measuring the performance of a database management system. Concurrent database operations may cause three problems: 1. Lost updates. 2. Non-repeatable reading. 3. Read "dirty data".

Jul 24, 2019 pm 03:17 PM

数据库

What is pointed out by using where clause in sql query

The where clause is used in sql queries to indicate the query conditions. The WHERE clause is used to extract records that meet specified criteria.

Jul 24, 2019 am 10:15 AM

SQL查询

Database backup and recovery solution

SQL SERVER backup method. Based on data security requirements, the recommended backup methods are a full backup once a week, a differential backup once a day, and a transaction log backup every half hour. Restoring a backup requires restoring the full backup first, then the differential backup, and then the transaction log backup. Restore the database to the state at the time of the transaction log backup

Jul 22, 2019 pm 06:22 PM

sql 数据库

sql command to update records

There are two usages of SQL update statements: 1. Update a column: UPDATE table name SET column name = new value WHERE column name = a certain value. 2. Update several columns: UPDATE table name SET column 1 name = new value, column 2 name = new value WHERE column name = a certain value

Jul 22, 2019 pm 02:51 PM

sql

What is sql statement

SQL (Structured Query Language, Structured Query Language) statement is a language that operates on the database.

Jul 22, 2019 am 11:40 AM

sql

What is the command to insert records in sql

The sql command to insert records is INSERT INTO. In SQL, you can use the INSERT INTO command to add all fields and specific columns to the data table.

Jul 22, 2019 am 10:22 AM

SQL，命令

What does sql refer to?

SQL (Structured Query Language) is a database language with multiple functions such as data manipulation and data definition. This language has interactive characteristics and can provide users with great convenience. Database management systems should make full use of SQL language to improve computer application systems. work quality and efficiency.

Jul 20, 2019 pm 03:53 PM

sql 数据库

MongoDB – Polymorphic schema built with schemas

Brief description: When all documents in a collection have a similar but not identical structure, we call it polymorphic pattern. Example: User posts need to be used in actual business. The general structure of the posts is the same, but the specific content needs to be displayed differently according to different post types.

Jul 01, 2019 pm 06:02 PM

MongoDB

MongoDB – Attribute schema built using schema

Go directly to understand attribute mode. It is particularly suitable for the following situations: there is a large document, but it actually has some similar fields, and a subset of these fields has the same characteristics. In the end, these subset fields actually need to be sorted or queried.

Jul 01, 2019 pm 04:37 PM

MongoDB

having usage

The function of the having clause is to filter the groups that meet the conditions. The having clause is restricted to the columns and aggregate expressions defined in the SELECT statement. The aggregate value needs to be referenced by repeating the aggregate function expression in the HAVING clause.

Jun 29, 2019 am 09:58 AM

having

Best Practices for MongoDB Indexes

Most developers know that indexing is faster. But in the actual process, we often encounter some questions & difficulties: the fields we query will have various cases. Do all fields involved in the query need to be indexed? How to choose between compound index and single field? Should I add both or a single field for each? This article attempts to explain the basic knowledge of indexing and answer the above questions

Jun 24, 2019 pm 05:36 PM

MongoDB 索引

What are the architectural characteristics of a database system

The architectural features of the database system are three-level schema structure and two-level mapping, namely schema, outer schema, inner schema, outer schema/schema mapping, and schema/inner schema mapping.

Jun 24, 2019 pm 04:29 PM

数据库系统的体系结构特征

What the database design process does not include

The database design process does not include algorithm design. The database design process mainly includes requirements analysis, conceptual structure design, logical structure analysis, database physical design, database implementation, database operation and maintenance stages.

Jun 20, 2019 pm 01:37 PM

数据库设计

What are the types and characteristics of databases?

Database types: Databases are usually divided into two categories, namely relational databases and non-relational databases. Features: Relational databases are easy to maintain, easy to use, and complex to operate. As a supplement to relational databases, non-relational databases can achieve high efficiency and high performance in specific scenarios and characteristic problems.

Jun 19, 2019 pm 01:28 PM

数据库种类及特点