Re: Please advice on a query

I have a table more or less like this:

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crs_id                some data                req

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25                       aaaaaaaa                 21

25                       aaaaaaaa                 19

17                       ccccccccc                 null

8                         dddddddd                 null

19                       eeeeeeee                 15

19                       xxxxxxxxx                  37

15                       fffffffffffffffff                  10

10                       gggggggg                   null

I need to delete rows according to the following criteria:

* Row with "crs_id = 25" must be deleted (only the second row) because "req = 19" and there is a row with "crs_id = 19" 

* Row with "crs_id = 19" must be deleted (only the first row) because "req = 15" and there is a row with "crs_id = 15"

* Row with "crs_id = 15" must be deleted because "req = 10" and there is a row with "crs_id = 10"

I have been struggling with this issue without a successful result.