Use of Oracle decode Functions

Today, the user requires that all data 0 cannot be involved in the average calculation. The idea is that the AVG function itself does not participate in the calculation of NULL data. Therefore, you only need to convert zero data to null, I thought it could be implemented using the case statement, but I found the decode function on the Internet, which is very good enough to meet my needs. The following is his usage.
Decode(Condition, value 1, translation value 1, value 2, translation value 2,... value n, translation value n, default value)

The function has the following meanings:
If condition = value 1 then
Return (translation value 1)
Elsif condition = value 2 then
Return (translation value 2)
......
Elsif condition = value n then
Return (translation value n)

Else
Return (default)
End if
· Usage:
1. Compare the size
SelectDecode(Sign (variable 1-variable 2),-1, variable 1, variable 2) from dual; -- smaller value
The sign () function returns 0, 1, and-1 respectively based on a value of 0, positive, or negative.

For example:
Variable 1 = 10, variable 2 = 20
Then sign (variable 1-variable 2) returns-1,DecodeThe decoded result is "variable 1", so that a smaller value is obtained.

2. Table and View Structure Conversion
There is a sales table sale with the following structure:
Month char (6) -- month
Billing number () -- monthly sales amount

The existing data is:
200001 1000
200002 1100
200003 1200
200004 1300
200005 1400
200006 1500
200007 1600
200101 1100
200202 1200
200301 1300

Data to be converted to the following structure:
Year char (4) -- year
Month1 number () -- sales amount in
Mon2number (February) -- sales amount in December
Month3 number (March) -- sales amount in December
Month4 number (April) -- sales amount in December
Month5 number (May) -- sales amount in December
Month6 number (June) -- sales amount in December
Month7 number (July) -- sales amount in December
Month8 number (August) -- sales amount in December
Month9 number (September) -- sales amount in December
Month10 number (October) -- sales amount in December
Month11 number (November) -- sales amount in December
Month12 number (December) -- sales amount in December

The SQL statement for structure conversion is:
Create or replace View
V_sale (year, month1, mon2, month3, month4, month5, month6, month7, month8, month9, month10, month11, month12)
As
Select
Substrb (month, 1, 4 ),
Sum (Decode(Substrb (month, 5, 2), '01', month, 0 )),
Sum (Decode(Substrb (month, 5, 2), '02', month, 0 )),
Sum (Decode(Substrb (month, 5, 2), '03', hour, 0 )),
Sum (Decode(Substrb (month, 5, 2), '04 ', month, 0 )),
Sum (Decode(Substrb (month, 5, 2), '05 ', month, 0 )),
Sum (Decode(Substrb (month, 5, 2), '06', month, 0 )),
Sum (Decode(Substrb (month, 5, 2), '07 ', month, 0 )),
Sum (Decode(Substrb (month, 5, 2), '08 ', hour, 0 )),
Sum (Decode(Substrb (month, 5, 2), '09', hour, 0 )),
Sum (Decode(Substrb (month, 5, 2), '10', hour, 0 )),
Sum (Decode(Substrb (month, 5, 2), '11', hour, 0 )),
Sum (Decode(Substrb (month, 5, 2), '12', hour, 0 ))
From sale
Group by substrb (month, 1, 4 );

This SQL statement is written in my project.
Select AVG (to_number (decode (rcql), 0, '', rcql) from dba03, this statement calculates the average value of the daily output and Zero is not involved in the operation.