2.select d.id,d.outer_code,row_number() over(partition by outer_code order by outer_code) row_flag from dict_depts_sour
1.select d.id,d.outer_code from dict_depts_source d order by outer_code(查看重复数据)
2.select d.id,d.outer_code,row_number() over(partition by outer_code order by outer_code) row_flag from dict_depts_source d(标识重复数据)
3.delete from dict_depts_source where id in(
select id from(select d.id,d.outer_code,row_number() over(partition by outer_code order by outer_code) row_flag from dict_depts_source d)t
where t.row_flag > 1)(删除重复数据)
4.select d.id,d.outer_code,row_number() over(partition by outer_code order by outer_code) row_flag from dict_depts_source d(检查删除效果)
How does MySQL differ from SQLite?Apr 24, 2025 am 12:12 AMThe main difference between MySQL and SQLite is the design concept and usage scenarios: 1. MySQL is suitable for large applications and enterprise-level solutions, supporting high performance and high concurrency; 2. SQLite is suitable for mobile applications and desktop software, lightweight and easy to embed.
What are indexes in MySQL, and how do they improve performance?Apr 24, 2025 am 12:09 AMIndexes in MySQL are an ordered structure of one or more columns in a database table, used to speed up data retrieval. 1) Indexes improve query speed by reducing the amount of scanned data. 2) B-Tree index uses a balanced tree structure, which is suitable for range query and sorting. 3) Use CREATEINDEX statements to create indexes, such as CREATEINDEXidx_customer_idONorders(customer_id). 4) Composite indexes can optimize multi-column queries, such as CREATEINDEXidx_customer_orderONorders(customer_id,order_date). 5) Use EXPLAIN to analyze query plans and avoid
Explain how to use transactions in MySQL to ensure data consistency.Apr 24, 2025 am 12:09 AMUsing transactions in MySQL ensures data consistency. 1) Start the transaction through STARTTRANSACTION, and then execute SQL operations and submit it with COMMIT or ROLLBACK. 2) Use SAVEPOINT to set a save point to allow partial rollback. 3) Performance optimization suggestions include shortening transaction time, avoiding large-scale queries and using isolation levels reasonably.
In what scenarios might you choose PostgreSQL over MySQL?Apr 24, 2025 am 12:07 AMScenarios where PostgreSQL is chosen instead of MySQL include: 1) complex queries and advanced SQL functions, 2) strict data integrity and ACID compliance, 3) advanced spatial functions are required, and 4) high performance is required when processing large data sets. PostgreSQL performs well in these aspects and is suitable for projects that require complex data processing and high data integrity.
How can you secure a MySQL database?Apr 24, 2025 am 12:04 AMThe security of MySQL database can be achieved through the following measures: 1. User permission management: Strictly control access rights through CREATEUSER and GRANT commands. 2. Encrypted transmission: Configure SSL/TLS to ensure data transmission security. 3. Database backup and recovery: Use mysqldump or mysqlpump to regularly backup data. 4. Advanced security policy: Use a firewall to restrict access and enable audit logging operations. 5. Performance optimization and best practices: Take into account both safety and performance through indexing and query optimization and regular maintenance.
What are some tools you can use to monitor MySQL performance?Apr 23, 2025 am 12:21 AMHow to effectively monitor MySQL performance? Use tools such as mysqladmin, SHOWGLOBALSTATUS, PerconaMonitoring and Management (PMM), and MySQL EnterpriseMonitor. 1. Use mysqladmin to view the number of connections. 2. Use SHOWGLOBALSTATUS to view the query number. 3.PMM provides detailed performance data and graphical interface. 4.MySQLEnterpriseMonitor provides rich monitoring functions and alarm mechanisms.
How does MySQL differ from SQL Server?Apr 23, 2025 am 12:20 AMThe difference between MySQL and SQLServer is: 1) MySQL is open source and suitable for web and embedded systems, 2) SQLServer is a commercial product of Microsoft and is suitable for enterprise-level applications. There are significant differences between the two in storage engine, performance optimization and application scenarios. When choosing, you need to consider project size and future scalability.
In what scenarios might you choose SQL Server over MySQL?Apr 23, 2025 am 12:20 AMIn enterprise-level application scenarios that require high availability, advanced security and good integration, SQLServer should be chosen instead of MySQL. 1) SQLServer provides enterprise-level features such as high availability and advanced security. 2) It is closely integrated with Microsoft ecosystems such as VisualStudio and PowerBI. 3) SQLServer performs excellent in performance optimization and supports memory-optimized tables and column storage indexes.
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