The EXTRACT function is a very efficient way to select a group of values, but if the expected result set is just a single object then you are better off using the CHOOSE function previously discussed.
EXTRACT函数是选择一组值的非常高效的方法，但是如果预期的结果集只是单一对象，那么最好使用前面介绍的choose函数。
The EXTRACT function is a very efficient way to select a group of values, but if the expected result set is just a single object then you are better off using the CHOOSE function previously discussed.
EXTRACT函数是选择一组值的非常高效的方法，但是如果预期的结果集只是单一对象，那么最好使用前面介绍的choose函数。
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