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- 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.
- SQL 3616 2019-07-01 18:02:05
- 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.
- SQL 2736 2019-07-01 18:04:56
- 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.
- SQL 23595 2019-07-29 14:07:27
- 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
- SQL 3280 2019-06-24 17:36:15
- 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.
- SQL 10891 2019-06-24 16:29:15
- 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.
- SQL 8374 2019-06-25 14:19:31
- 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.
- SQL 9184 2019-06-20 09:03:04
- Detailed explanation of sql stored procedure examples
- A stored procedure is a set of SQL statements designed to accomplish specific functions. It is similar to a programming language and includes data types, process control, input and output, and its own function library. We can learn more about the stored procedure in detail through the instance table Student, such as a parameterless stored procedure: select all the information in the Student table.
- SQL 8362 2019-06-15 14:05:23
- What are the nine commonly used statements in SQL
- The nine commonly used statements in SQL include create database, drop database, sql server, backup database, drop table tabname, drop index idxname, drop view view
- SQL 11909 2019-06-15 11:16:42
- What is the command to modify the table structure in sql statement?
- The command in the SQL statement to modify the table structure is ALTER TABLE. The ALTER TABLE statement is used to add, delete, or modify columns in an existing table.
- SQL 28966 2019-06-19 16:05:44
- What is the sql modification statement?
- The sql modification statement is an UPDATE statement. The UPDATE statement is used to update existing records in the table. Please pay attention to the WHERE clause in the SQL UPDATE statement! The WHERE clause specifies which record or records need to be updated. If you omit the WHERE clause, all records will be updated!
- SQL 8035 2019-06-18 14:37:28
- What is the database add statement?
- The database add statement is the INSERT INTO statement. The INSERT INTO statement is used to insert new records into the table. The INSERT INTO statement can be written in two forms: the first form does not need to specify the column name of the data to be inserted, and only needs to provide the inserted value; the second form requires Specify the column name and the value to be inserted.
- SQL 29872 2019-06-18 14:39:04
- A brief discussion of database stored procedures
- Database stored procedures: Stored procedures are methods, with similar method names, variables to be passed by the method, and return results, so stored procedures have stored procedure names, stored procedure parameters, and return values.
- SQL 40309 2020-09-12 14:54:54
- Detailed explanation of database stored procedures
- Stored procedures can be viewed as stored t-sql scripts in the database. Why use stored procedures? 1. Increase performance; 2. Enhance security; 3. Use non-database technology in transact-sql; 4. Programming mode - use external programming language calls.
- SQL 14609 2019-06-20 14:16:12
- What are the two methods of database backup?
- The two methods for database backup are: 1. Use mysqldump combined with the exec function for database backup; 2. Use the [php+mysql+header] function for database backup.
- SQL 32088 2020-09-12 16:34:30
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