MySQL行转列技巧及其应用详解（mysql行转列详解）

MySQL is an open-source database management system that is commonly used for web development. One of its most powerful features is its ability to transform data from rows to columns and vice versa. This functionality can be used to obtain valuable insights from large collections of data, as well as reorder and analyze data sets for better storage and processing. In this article, we will discuss the different techniques for converting rows to columns and their various applications.

Firstly, let’s cover one of the most common methods for row to column conversion – the PIVOT operator. The PIVOT operator is a part of the SELECT statement and is used to rearrange rows into columns by aggregating different values and grouping them by one or more columns. An example of how the PIVOT operator works can be seen below where the data is grouped by Language and the count of the records is selected by using the PIVOT operator.

Example of using PIVOT statement

SELECT *

FROM

table

PIVOT

(COUNT(*)

FOR Language IN (‘Python’, ‘Java’, ‘C++’))

As you can see, the PIVOT Operator creates three columns for Python, Java, and C++ and adds the count of the records for each language in its corresponding column. While the PIVOT Operator works great for this example, with more complicated data sets it can become time-consuming and difficult to use.

Another popular technique for row to column conversion is the UNPIVOT operator. This operator works in the opposite way of the PIVOT operator and is used to convert columns into rows. It works by transforming the different columns that contain multiple values into a single row with multiple entries. An example of how the UNPIVOT operator works can be seen below.

Example of using UNPIVOT statement

SELECT

*

FROM

table

UNPIVOT

(score FOR Student IN (John, Mary, Harry))

The UNPIVOT operator uses the column names of the data set (John, Mary, and Harry) as the names of the new columns and the scores recorded in each column become the row entries. As you can see, both the PIVOT and UNPIVOT operators can be useful for quickly rearranging, aggregating, and analysing data sets.

Finally, there is also the TRANSFORM Operator which can be used for row-to-column conversion. The TRANSFORM operator is similar to the PIVOT operator but with an added bonus; it allows users to apply functions to the data such as SUM(), COUNT(), AVG(), etc. before transforming data from rows to columns.

Example of using TRANSFORM statement

SELECT

*

FROM

table

TRANSFORM

COUNT(*)

FOR Language IN (‘Python’, ‘Java’, ‘C++’)

The TRANSFORM operator works similar to the PIVOT Operator but also allows a user to perform calculations on the data before transforming it into columns.

In conclusion, MySQL provides a range of different operators and techniques to help you convert rows to columns and vice versa. The PIVOT, UNPIVOT, and TRANSFORM operators are widely used for their powerful and convenient data transformation capabilities. By using these techniques, users can quickly and easily derive insights and patterns from their data sets.