CASE `product_path` when `product_path` = '' then `product_path` end

这段 SQL 语句中的 CASE 表达式是没有实际意义的，因为它的逻辑就是在判断 `product_path` 是否为空字符串，如果为空字符串，则返回 `product_path`，否则返回 NULL，而这个判断条件永远为真，因为 `product_path` = '' 已经被作为 CASE 表达式的条件了，所以这个表达式实际上就是一个等同于 `product_path` 的字段，不会有任何实际的计算结果。

如果您想要实现在 `product_path` 字段为空字符串的时候返回一个默认值，可以使用如下的 SQL 语句：

SELECT
    CASE
        WHEN product_path = '' THEN 'default_value'
        ELSE product_path
    END AS product_path
FROM your_table;

这个语句将在 `product_path` 字段为空字符串时返回一个默认值，否则返回原始的 `product_path` 字段。希望这可以帮助您！

相关问题

for test_path in tests_path:

As an AI language model, I can certainly help you understand what the code "for test_path in tests_path:" may represent, and how it could be used in a programming context.

The code "for test_path in tests_path:" is a Python loop statement that iterates over a sequence of values, in this case, a list of file paths, represented by the variable "tests_path". The loop assigns each value in the sequence to the variable "test_path" and executes the body of the loop for each iteration.

For example, if "tests_path" contains the following file paths:

tests_path = ['/home/user/tests/test1.py', '/home/user/tests/test2.py', '/home/user/tests/test3.py']

The loop statement:

for test_path in tests_path:
# do something with test_path

will execute the code block inside the loop three times, with "test_path" taking the value of each file path in turn, allowing you to perform some operation on each file.

In summary, "for test_path in tests_path:" is a loop statement in Python that allows you to iterate over a sequence of values, such as a list of file paths, and perform some operation on each value.

CMAKE_PREFIX_PATH

CMAKE_PREFIX_PATH是一个cmake变量，用于指定在查找包文件时要搜索的路径。在CONFIG模式下，CMake会通过查找名为<PackageName>Config.cmake或者<lower-case-package-name>-config.cmake的文件来查找包文件。CMAKE_PREFIX_PATH可以包含特定路径和系统环境变量PATH指定的路径。

在一般的使用中，可以通过设置CMAKE_PREFIX_PATH来指定需要搜索的路径。例如，可以使用set命令来添加路径：
set(CMAKE_PREFIX_PATH ${CMAKE_PREFIX_PATH} "C:/Qt/Qt5-msvc14/5.6/msvc2015_64")

这样，CMake在查找包文件时就会在CMAKE_PREFIX_PATH指定的路径以及系统环境变量PATH指定的路径下进行搜索。这样可以确保CMake能够找到所需的包文件，并成功进行构建和编译。<span class="em">1</span><span class="em">2</span><span class="em">3</span><span class="em">4</span>