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- What are the characteristics of nosql database
- The characteristics of nosql database are: 1. Easy to expand; 2. Large data volume and high performance; 3. Flexible data model; 4. High availability. There are many types of NoSQL databases, but they all have a common feature, that is, they all remove the relational characteristics of relational databases.
- SQL 35118 2020-07-03 11:05:00
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- What are the relational operations of the database?
- The relational operations of the database include: 1. Selection operation, which selects all tuples that meet given conditions from a relation R; 2. Projection operation, which selects certain specified attributes from all attributes of a relation R; 3. Connection operation, It selects tuples that meet certain conditions between attributes from the generalized Cartesian product of two relationships to form a new relationship.
- SQL 29985 2020-07-03 09:28:03
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- What is the meaning of group by in sql query
- The meaning of group by in SQL query is to combine the total function to group the result set according to one or more columns. Its function is to divide a data set into several small areas through certain rules, and then target several A small area for data processing.
- SQL 22891 2020-07-02 17:19:54
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- What kind of database is hbase?
- HBase is a distributed, column-oriented open source database. The technology comes from the Google paper "Bigtable: A distributed storage system for structured data" written by Fay Chang.
- SQL 10854 2020-07-01 16:30:28
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- What are the methods for sql optimization?
- SQL optimization methods: 1. Try to avoid using [select *], useless fields will reduce query efficiency; 2. Avoid using in and not in, you can choose between and exists instead; 3. Avoid using or, you can choose union instead.
- SQL 8891 2020-07-01 15:55:05
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- What are non-relational databases?
- Non-relational databases include: 1. MongoDB, which is a document-oriented open source NoSQL database; 2. Cassandra, which was developed by Facebook for inbox search; 3. Redis, which is the most famous key-value store.
- SQL 37242 2020-07-01 15:24:49
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- What are distributed databases?
- Distributed databases include: 1. In the direction of the Internet of Things, time series database products meet the collection, storage and statistics of IoT data, such as InfluxDB, Kudu, kdb, and OpenTSDB; 2. In the direction of transaction relationships, Ant Financial Oceanbase and Tencent TDSQL.
- SQL 20598 2020-07-01 15:14:16
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- What is the priority of SQL statement execution order?
- The execution order priority of SQL statements from high to low is: the statement after the from keyword, the statement after the where keyword, the statement after "group by", the statement after select, and the statement after "order by".
- SQL 22886 2020-07-01 09:44:34
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- What is SQL Interface
- SQL Interface refers to the SQL interface, which means that it accepts the user's SQL commands and returns the results that the user needs to query. For example, select from is to call the SQL Interface.
- SQL 4173 2020-07-01 09:10:36
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- How to create student table using sql statement?
- Steps: 1. Open "sql server"; 2. Use "creat table student();" to create a table; 3. Use "char()" to define the type of name, gender, and age; 4. Use "insert into student values" ();" Just define the table attributes.
- SQL 35467 2020-06-30 10:16:34
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- What is slow query
- In addition to using EXPLAIN to output the execution plan, the method of analyzing MySQL statement query performance can also allow MySQL to record statements that query more than the specified time. We call SQL statement queries that exceed the specified time "slow queries".
- SQL 5468 2020-06-29 16:22:37
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- What does database read-write separation mean?
- The separation of database read and write means to ensure the stability of database products. Many databases have dual-machine hot backup functions. That is to say, the first database server is a production server that provides external addition, deletion, and modification services; the second database server mainly performs read operations.
- SQL 8396 2020-06-29 13:24:15
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- How to pronounce sql server?
- The pronunciation of "sql server" is [sikəu 'sə:və]. "SQL Server" is a relational database management system launched by Microsoft; it has the advantages of ease of use, good scalability, and a high degree of integration with related software.
- SQL 20366 2020-06-24 09:55:56
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- What are the four parts of the function of sql?
- The four parts are: 1. Data definition, which is used to define the creation and undoing operations of SQL schema, basic tables, views and indexes; 2. Data manipulation, which is divided into two categories: data query and data update; 3. Data control, including basic Authorization of tables and views, description of integrity rules, transaction control, etc.; 4. Regulations on the use of embedded SQL.
- SQL 20593 2020-06-23 17:13:00
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- What needs to be modified to ensure data independence of the database?
- To ensure the data independence of the database, what needs to be modified is the mapping between the schema and the internal schema. DBMS provides two layers of images, namely: external schema/schema image and schema/internal schema image; the image from the external schema to the schema ensures the logical independence of the data; the image from the schema to the internal schema ensures the physical integrity of the data. independence.
- SQL 13204 2020-07-23 13:13:58
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