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Technical Articles

Database

SQL

SQL server high concurrency generates unique order number

We can use stored procedures and data tables to build a table and create stored procedures. The stored procedure is responsible for generating order numbers, and the table is responsible for handling uniqueness issues.

Aug 29, 2020 pm 12:01 PM

SQL server

What are the two categories of data operations in relational databases?

Data operations in relational databases are divided into two categories: query and update. Query statements are used for various retrieval operations, and update operations are used for operations such as insertion, deletion, and modification.

Aug 28, 2020 pm 04:45 PM

关系数据库数据操作

When creating a crosstab query, where does the value of the column header field appear in the crosstab?

When you create a crosstab query, the value of the column header field appears in the crosstab at the first row. A crosstab query groups the fields from a table. One group of columns is on the left side of the data table as the row fields of the crosstab, and the other group of columns is on the top of the data table as the column fields of the crosstab.

Aug 28, 2020 pm 04:18 PM

交叉表查询数据库

What is the syntax structure of select statement in SQL?

The syntax structure of the select statement in SQL is: "SELECT select_list [ INTO..] FROM table_name [ WHERE...] [ GROUP BY...][ HAVING...][ ORDER BY...];".

Aug 28, 2020 pm 01:24 PM

SQL select语句

What are the commonly used methods for sql optimization?

Commonly used methods for sql optimization include: 1. Try to avoid full table scans, and consider establishing indexes on the columns involved in where and order by; 2. Try to avoid making null value judgments on fields in the where clause; 3. Use with caution in and not in; 4. Try to avoid large transaction operations and improve system concurrency.

Aug 24, 2020 pm 01:12 PM

sql优化

Why does invalid column index appear in sql

Reasons for invalid column index in sql: 1. The placeholder is inconsistent with the number of parameters; 2. SQL splicing error, please note that each [%] must be included with [''], and spliced with the parameters with [||]; 3 , wrong annotation.

Aug 22, 2020 am 10:07 AM

sql 列索引

What is the difference between deleting table data and deleting table structure in SQL?

The difference between deleting table data and deleting table structure in SQL: 1. Deleting table data, the table structure is still there, while deleting table structure means deleting the entire table, including structure and data; 2. Different commands, deleting table data [ delete from table name], and the delete table structure is [drop table table name].

Aug 19, 2020 pm 02:42 PM

SQL 表数据表结构

What are the characteristics of a trigger?

Characteristics of triggers: 1. Automatic execution; triggers are activated immediately after any modifications are made to the data in the table. 2. Cascading updates; triggers can make cascading changes through related tables in the database. 3. Strengthen constraints. 4. Track changes. 5. Enforce business logic; triggers can be used to perform administrative tasks and enforce complex business rules that affect the database.

Aug 18, 2020 am 11:49 AM

触发器 SQL server

How to recover accidentally deleted database data

How to recover accidentally deleted database data: first run Recovery for SQL Server and select the recovered data in recovery; then select Custom and select the [search..] option; then select the target folder and click Start; finally select the target database .

Aug 12, 2020 am 09:55 AM

数据库数据恢复

Briefly describe the basic principles of database design

Basic principles of database design: 1. Store data with the same theme in a data table; 2. Try to eliminate redundancy and improve the speed of database access; 3. When designing the data table structure, the dynamic adaptation of the table structure should be considered sex.

Aug 10, 2020 pm 03:03 PM

数据库设计基本原则

Does sql between include both ends?

In SQL, the BETWEEN operator is used to select values within the data range between two values. Among them, "between and" includes boundary values, that is, including both ends; "not between" does not include boundary values.

Jul 28, 2020 pm 03:39 PM

sql between

How to set primary key in sql database?

Setting method: 1. Use the SQL Server Management Studio tool to connect to the database; 2. Expand "Table" in the database, right-click the data table that needs to be set, and select "Design"; 3. In the table designer interface, right-click the corresponding OK, select "Set Primary Key" to complete the setting of the primary key, click Save.

Jul 28, 2020 am 10:54 AM

sql 主键

What is SQL's advanced and oriented operating language?

SQL is a highly non-procedural and set-oriented operating language. When using SQL to perform data operations, users only need to ask "what to do" instead of specifying "how to do it". Therefore, users do not need to know the access path. The selection of the access path and the operation process of the SQL statement are automatically completed by the system; SQL uses sets Operation method.

Jul 24, 2020 pm 03:50 PM

sql 结构化查询语言

How to differentiate between left outer join, right outer join and full outer join?

A left outer join will return all records in the left table that are equal to the join fields in the right table; null if there is no data in the right table. A right outer join will return all records in the right table that are equal to the join fields in the left table; null if there is no data in the left table. A full outer join will return all records in the left and right tables that are equal to the join fields in the left and right tables.

Jul 21, 2020 pm 03:05 PM

左外连接右外连接全外连接