Native SQL - instead of FOR and AT Clauses

[cognosun]

Gurus,

Can anyone help me how to convert (roughly) this Cognos SQL to Oracle SQL, which is written for one derived column.

SUM(MAX(COLUMN A for COLUMN  B) at COLUMN B) / COUNT ( COLUMN B at COLUMN B)
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I need native SQL for the same, but with above expression, it's splitting Column B as seperate column, and sum() function is taking away decimals from the output.

Many Thanks in Advance
Joys