Order of columns(variables) in proc append - sas

Question

I am fairly new to SAS.
I wanted to append two datasets Dataset1 and Dataset2
The order of columns in Dataset1 is A B C
The order of columns in Dataset2 is b A c
Note the case of the column names(upper case and lower case)
So if I do
PROC APPEND BASE=Dataset1 DATA=Dataset2 FORCE;
RUN;
Will the appending happend in a desired way :
A should append to A
B should append to b
C should append to c

Answer 1

Neither case nor position matter for columns.
Columns are identified by their names, not their position.
Examples can help demonstrate this; try running the following one step at a time; read the comments, check the log and examine the data sets:
/* creates data set have1 with columns a (char), b (numeric) then c (numeric) */
data have1;
length a $ 1;
input a b c;
datalines;
1 2 3
4 5 6
7 8 9
;
/* creates data set have2 with columns b (char), a (numeric) then c (numeric) */
data have2;
length b $ 1;
input a b c;
datalines;
1 2 3
4 5 6
7 8 9
;
/* attempts append, but as a & b have different types, missing values result */
proc append base = have1
data = have2
force
;
run;
/* creates data set have3 with columns a (char), b (numeric) then c (numeric) */
data have3;
length a $ 1;
input a b c;
datalines;
1 2 3
4 5 6
7 8 9
;
/* creates data set have4 with columns b (numeric), a (char) then c (numeric) */
data have4;
length b 8;
length a $ 1;
input a b c;
datalines;
1 2 3
4 5 6
7 8 9
;
/* Appends successfully as variable types are the same even though order is different. */
/* Columns are identified by their names, not their position. */
proc append base = have3
data = have4
force
;
run;
EDIT: In answer to the question in the comment:
Having same type but different format.Example num type but DATE9.
format and other column has num type but ddmmyy format will this
cause any problem ?
The format of a variable affects the way it is displayed, the underlying data remains unchanged, so appending one numeric column with another is possible, the only difference would be is that the appended data will be in the same format as the base data, as noted by #J_Lard in the first comment to your question.
Again, an example might help to demonstrate this:
/* creates data set have5 with columns a (numeric, formst date9.) and text */
data have5;
format a date9.;
input text $char10.;
a = input(text,ddmmyy10.);
datalines;
31/07/2018
;
/* creates data set have6 with columns a (numeric, formst ddmmyy.) and text */
data have6;
format a ddmmyy.;
input text $char10.;
a = input(text,ddmmyy10.);
datalines;
31/07/2018
;
/* appends, but see warning in log about format */
proc append base = have5
data = have6
force
;
run;
Hopefully you can see the approach to take if you have more questions you need answering (create test data then append / process). If you still have problems then I would suggest asking a new question, with a link to this one, if relevant, supplying test data steps for others to run and the code you've tried with any log messages.