declare @TableName nvarchar(250)--定义当前操作的数据表名变量set @TableName=
--SQL批量删除指定数据表中的所有字段说明属性
--现象:执行select * from sys.extended_properties where value is null;显示出多条记录类似于[1 OBJECT_OR_COLUMN 2372069 1 MS_Description NULL]
--操作:执行delete from sys.extended_properties where value is null;提示[不允许对系统目录进行即席更新]
--功能说明:因为错误的操作将到了字段描述为NULL添加到系统数据表sys.extended_properties中,最终需要批量删除掉后再添加字段描述
declare @TableName nvarchar(250)--定义当前操作的数据表名变量
set @TableName='user'--指定要查询的数据表名称(此处的数据表名user需要更新为你的数据库中的已有数据表名)
declare @ColumnName nvarchar(250)--游标中的当前查询的字段名称
declare @ColumnDescription nvarchar (250)--游标中的当前查询的字段说明
--声明读取数据表中所有字段说明的游标
declare mycursor cursor for select a.name,CAST(g.value AS nvarchar) from sys.columns a left join sys.extended_properties g on (a.object_id = g.major_id AND a.column_id=g.minor_id) where object_id=OBJECT_ID(''+@TableName+'') order by object_id,a.column_id
--打开游标
open mycursor
--从游标里取出数据赋值到约束名称变量中
fetch next from mycursor into @ColumnName,@ColumnDescription
--如果游标执行成功
while (@@fetch_status=0)
begin
if(@ColumnDescription is null)
begin
print '当前数据表['+@TableName+']字段['+@ColumnName+']对应的说明为空'
--删除字段的描述属性值为NULL的记录
--EXEC sp_dropextendedproperty 'MS_Description','user',dbo,'table','数据表名称', 'column','字段名称'
EXEC sp_dropextendedproperty 'MS_Description','user',dbo,'table',@TableName,'column',@ColumnName
end
else
begin
--查询当前找到的字段说明
print '当前数据表['+@TableName+']字段['+@ColumnName+']对应的说明是['+@ColumnDescription+']'
end
--用游标去取下一条记录
fetch next from mycursor into @ColumnName,@ColumnDescription
end
--关闭游标
close mycursor
--撤销游标
deallocate mycursor

The steps to create and manage user accounts in MySQL are as follows: 1. Create a user: Use CREATEUSER'newuser'@'localhost'IDENTIFIEDBY'password'; 2. Assign permissions: Use GRANTSELECT, INSERT, UPDATEONmydatabase.TO'newuser'@'localhost'; 3. Fix permission error: Use REVOKEALLPRIVILEGESONmydatabase.FROM'newuser'@'localhost'; then reassign permissions; 4. Optimization permissions: Use SHOWGRA

MySQL is suitable for rapid development and small and medium-sized applications, while Oracle is suitable for large enterprises and high availability needs. 1) MySQL is open source and easy to use, suitable for web applications and small and medium-sized enterprises. 2) Oracle is powerful and suitable for large enterprises and government agencies. 3) MySQL supports a variety of storage engines, and Oracle provides rich enterprise-level functions.

The disadvantages of MySQL compared to other relational databases include: 1. Performance issues: You may encounter bottlenecks when processing large-scale data, and PostgreSQL performs better in complex queries and big data processing. 2. Scalability: The horizontal scaling ability is not as good as Google Spanner and Amazon Aurora. 3. Functional limitations: Not as good as PostgreSQL and Oracle in advanced functions, some functions require more custom code and maintenance.

MySQL supports four JOIN types: INNERJOIN, LEFTJOIN, RIGHTJOIN and FULLOUTERJOIN. 1.INNERJOIN is used to match rows in two tables and return results that meet the criteria. 2.LEFTJOIN returns all rows in the left table, even if the right table does not match. 3. RIGHTJOIN is opposite to LEFTJOIN and returns all rows in the right table. 4.FULLOUTERJOIN returns all rows in the two tables that meet or do not meet the conditions.

MySQL's performance under high load has its advantages and disadvantages compared with other RDBMSs. 1) MySQL performs well under high loads through the InnoDB engine and optimization strategies such as indexing, query cache and partition tables. 2) PostgreSQL provides efficient concurrent read and write through the MVCC mechanism, while Oracle and Microsoft SQLServer improve performance through their respective optimization strategies. With reasonable configuration and optimization, MySQL can perform well in high load environments.

InnoDBBufferPool reduces disk I/O by caching data and indexing pages, improving database performance. Its working principle includes: 1. Data reading: Read data from BufferPool; 2. Data writing: After modifying the data, write to BufferPool and refresh it to disk regularly; 3. Cache management: Use the LRU algorithm to manage cache pages; 4. Reading mechanism: Load adjacent data pages in advance. By sizing the BufferPool and using multiple instances, database performance can be optimized.

Compared with other programming languages, MySQL is mainly used to store and manage data, while other languages such as Python, Java, and C are used for logical processing and application development. MySQL is known for its high performance, scalability and cross-platform support, suitable for data management needs, while other languages have advantages in their respective fields such as data analytics, enterprise applications, and system programming.

MySQL is worth learning because it is a powerful open source database management system suitable for data storage, management and analysis. 1) MySQL is a relational database that uses SQL to operate data and is suitable for structured data management. 2) The SQL language is the key to interacting with MySQL and supports CRUD operations. 3) The working principle of MySQL includes client/server architecture, storage engine and query optimizer. 4) Basic usage includes creating databases and tables, and advanced usage involves joining tables using JOIN. 5) Common errors include syntax errors and permission issues, and debugging skills include checking syntax and using EXPLAIN commands. 6) Performance optimization involves the use of indexes, optimization of SQL statements and regular maintenance of databases.


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