让SELECT 查询结果额外增加自动递增序号
如果数据表本身并不内含自动地增编号的字段时,要怎么做才能够让SELECT查询结果,额外增加自动递增序号呢?我们提供下列五种方法供您参考: 自增长 USE 2 GO 3 4 /* 方法一*/ 5 6 SELECT序号= (SELECT COUNT(客户编号) FROM 客户 AS LiMing 7 WHERE LiMing.
如果数据表本身并不内含自动地增编号的字段时,要怎么做才能够让SELECT查询结果,额外增加自动递增序号呢?我们提供下列五种方法供您参考: 自增长USE 2 GO 3 4 /* 方法一*/ 5 6 SELECT序号= (SELECT COUNT(客户编号) FROM 客户 AS LiMing 7 WHERE LiMing.客户编号<= Chang.客户编号), 8 客户编号,公司名称 9 FROM客户 AS Chang ORDER BY 1; 10 GO 11 12 /* 方法二: 使用SQL Server 2005 独有的RANK() OVER () 语法*/ 13 SELECT RANK() OVER (ORDER BY 客户编号 DESC) AS 序号, 14 客户编号,公司名称 15 FROM客户; 16 GO 17 18 /* 方法三*/ 19 SELECT序号= COUNT(*), LiMing.客户编号, LiMing.公司名称 20 FROM 客户 AS LiMing, 客户AS Chang 21 WHERE LiMing.客户编号>= Chang.客户编号 22 GROUP BY LiMing.客户编号, LiMing.公司名称 23 ORDER BY 序号; 24 GO 25 26 /* 方法四 27 建立一个「自动编号」的字段,然后将数据新增至一个区域性暂存数据表, 28 然后由该区域性暂存数据表中,将数据选取出来,最后删除该区域性暂存数据表 29 */ 30 SELECT序号= IDENTITY(INT,1,1),管道,程序语言,讲师,资历 31 INTO #LiMing 32 FROM问券调查一; 33 GO 34 SELECT * FROM #LiMing; 35 GO 36 DROP TABLE #LiMing; 37 GO 38 39 /* 40 方法五 41 使用 SQL Server 2005 独有的ROW_NUMBER() OVER () 语法 42 搭配 CTE (一般数据表表达式,就是 WITH 那段语法)选取序号2 ~ 4 的数据 43 */ 44 WITH排序后的图书 AS 45 (SELECT ROW_NUMBER() OVER (ORDER BY 客户编号 DESC) AS 序号, 46 客户编号,公司名称 47 FROM 客户) 48 SELECT * FROM 排序后的图书 49 WHERE序号 BETWEEN 2 AND 4; 50 GO

ACID attributes include atomicity, consistency, isolation and durability, and are the cornerstone of database design. 1. Atomicity ensures that the transaction is either completely successful or completely failed. 2. Consistency ensures that the database remains consistent before and after a transaction. 3. Isolation ensures that transactions do not interfere with each other. 4. Persistence ensures that data is permanently saved after transaction submission.

MySQL is not only a database management system (DBMS) but also closely related to programming languages. 1) As a DBMS, MySQL is used to store, organize and retrieve data, and optimizing indexes can improve query performance. 2) Combining SQL with programming languages, embedded in Python, using ORM tools such as SQLAlchemy can simplify operations. 3) Performance optimization includes indexing, querying, caching, library and table division and transaction management.

MySQL uses SQL commands to manage data. 1. Basic commands include SELECT, INSERT, UPDATE and DELETE. 2. Advanced usage involves JOIN, subquery and aggregate functions. 3. Common errors include syntax, logic and performance issues. 4. Optimization tips include using indexes, avoiding SELECT* and using LIMIT.

MySQL is an efficient relational database management system suitable for storing and managing data. Its advantages include high-performance queries, flexible transaction processing and rich data types. In practical applications, MySQL is often used in e-commerce platforms, social networks and content management systems, but attention should be paid to performance optimization, data security and scalability.

The relationship between SQL and MySQL is the relationship between standard languages and specific implementations. 1.SQL is a standard language used to manage and operate relational databases, allowing data addition, deletion, modification and query. 2.MySQL is a specific database management system that uses SQL as its operating language and provides efficient data storage and management.

InnoDB uses redologs and undologs to ensure data consistency and reliability. 1.redologs record data page modification to ensure crash recovery and transaction persistence. 2.undologs records the original data value and supports transaction rollback and MVCC.

Key metrics for EXPLAIN commands include type, key, rows, and Extra. 1) The type reflects the access type of the query. The higher the value, the higher the efficiency, such as const is better than ALL. 2) The key displays the index used, and NULL indicates no index. 3) rows estimates the number of scanned rows, affecting query performance. 4) Extra provides additional information, such as Usingfilesort prompts that it needs to be optimized.

Usingtemporary indicates that the need to create temporary tables in MySQL queries, which are commonly found in ORDERBY using DISTINCT, GROUPBY, or non-indexed columns. You can avoid the occurrence of indexes and rewrite queries and improve query performance. Specifically, when Usingtemporary appears in EXPLAIN output, it means that MySQL needs to create temporary tables to handle queries. This usually occurs when: 1) deduplication or grouping when using DISTINCT or GROUPBY; 2) sort when ORDERBY contains non-index columns; 3) use complex subquery or join operations. Optimization methods include: 1) ORDERBY and GROUPB


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