TABLE1:
    A  |  B  |  C
---------------------
    1  |  9  |  0
    2  |  7  |  0
    4  |  8  |  0
    3  |  6  |  0

TABLE1:
    A  |  B  |  C
---------------------
    1  |  9  |  0.25
    2  |  7  |  0.25
    4  |  8  |  0.25
    3  |  6  |  0.25

UPDATE TABLE
SET C = 1/COUNT(*)

Error: ERROR: aggregate functions are not allowed in UPDATE
Position: 21