In addition to what tobyink and Laurent_R just said: in your case, when you are sorting data from just one day (or even one month), you can sort by the default (complete record) without splitting or transforming. Of course (epending on how long your records are), sort might lose - performancewise - what you gain by omitting those steps, but even then

• if you need to run this just once, run time does not matter as much as programming time
• if specifications/requirements change relatively often (or are not yet stable), it is more important to have code that is easy to understand than code that is efficient

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