window are not restricted and thus the window starts at the first row
of a partition or terminates at the last row of a partition, respectively.
CURRENT ROW. This option specifies a window as starting or end-
ing according to the ROW or RANGE specification options.
<expression> PRECEDINGor <expression> FOLLOWING.
Applies an expression to start or end points of the window.
Figure 9.7 shows an example using the windowing clause. The total adds
up the current row plus the two preceding and two following rows. Can
this be done with regular Oracle SQL? Probably yes, but with great diffi-
culty and enormously ...
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