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2024年4月17日发(作者：同步fifo判断空满)

sqlserver一行值多列转化为多行的方法

Transposing rows of data into columns, or vice versa, is a common

requirement when working with SQL databases. One frequent

scenario where this is necessary is when data is stored in a

denormalized form, with multiple values for a single entity stored in

a single row as a delimited list.

将数据的行与列互相转置是在处理SQL数据库时经常遇到的需求。一个常

见的情况是当数据以非规范化的形式存储时，单个实体的多个值存储在单行

中作为分隔列表。在这种情况下， 我们需要将单行值多列转化为多行值单

列的形式，以便进一步分析和处理。

There are several ways to achieve this in SQL Server. One approach is

to use the `UNPIVOT` operator, which can be used to unpivot

columns of data into rows. This allows for a straightforward

transformation of the data, and is particularly useful when the

number of columns to unpivot is small and known ahead of time.

另一个方法是使用UNPIVOT运算符，它可以用于将数据的列转化为行。这

种方法可以对数据进行直接的转换，并且在需要转化的列数较小并且事先已

知的情况下非常有用。

Another common method is to use a combination of the `CROSS

APPLY` or `CROSS JOIN` operators, along with the `VALUES` clause,

to split the delimited values into multiple rows. This approach

requires a bit more manual effort to write the query, but it offers

more flexibility and can handle a larger number of columns.

另一个常见的方法是使用CROSS APPLY或CROSS JOIN运算符，并结合

VALUES子句，将分隔的值拆分为多行。这种方法需要更多的手动编写查询

的工作，但它提供了更多的灵活性，可以处理更多的列。

In some cases, where the number of columns to unpivot is dynamic

or unknown, it may be necessary to use dynamic SQL to generate the

unpivoting query at runtime. While this approach can be more

complex and potentially less efficient, it allows for greater flexibility

and can handle scenarios where the structure of the data may

change over time.

在一些情况下，当需要转化的列数是动态或者未知的时，可能需要使用动态

SQL来在运行时生成转化查询。虽然这种方法可能更加复杂且效率可能不高，

但它允许更大的灵活性，并且可以处理数据结构随时间变化的情况。

It's important to consider the performance implications of each

approach when transposing rows into columns, especially when

working with large datasets. Testing different methods and analyzing

the execution plans can help identify the most efficient solution for a

specific scenario. Additionally, considering the frequency of data

transposition and the impact on overall system performance can

guide the choice of the most suitable method.

转化行值为列的时候，要考虑每种方法的性能影响，特别是处理大型数据集

时。测试不同的方法并分析执行计划可以帮助确定特定情况下最有效的解决

方案。此外，考虑数据转换的频率以及对整个系统性能的影响，可以指导选

择最合适的方法。

In conclusion, there are various methods for transposing rows of

data into columns in SQL Server, each with its own strengths and

considerations. Whether using the UNPIVOT operator, a combination

of CROSS APPLY or CROSS JOIN with the VALUES clause, or dynamic

SQL, it's important to weigh the trade-offs of each approach and

consider the specific requirements of the scenario at hand. By

carefully evaluating the performance implications and flexibility of

each method, it's possible to determine the most suitable approach

for achieving the desired data transformation.

总之，在SQL Server中有各种方法可以将数据的行转化为列，每种方法都

有其自身的优势和考虑因素。无论是使用UNPIVOT运算符，CROSS

APPLY或者CROSS JOIN与VALUES子句的组合，还是动态SQL，在权衡

每种方法的取舍并考虑具体的场景要求时，都非常重要。通过仔细评估每种

方法的性能影响和灵活性，可以确定实现所需数据转换的最合适方法。


本文标签： 方法 数据 考虑 转化 需要

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