What is a Sort key? What r the different tpes of Sort Keys u have in SAP(FICO)

sort Key: When u post the line item in GL account, the field
called Assignment is populated, and when u run the report of
the GL Account ( GL account line item report), the system by
default sort the value specified assignment field.

 
 
  `001  Posting Date
 
 
  `012  vendor no
 
 
  `014  Purchase order
 
 
  `018  Asset number
 
 
  `031  Customer number

Why we are using sort keys.

Straight answer to this is sort key offers great help in 
Automatic Clearing.

First we understand how does it function. If you have 
created Bank GL and there you have used 001 (posting date) 
as sort key then whenever you make entry for that bank Gl 
your sort key "Posting date" is automatically updated 
in "Assignment" field unless you manually insert anything 
in assignment field.

Let's take a simple example for why sort keys are helpful.

Suppose, there is GR/IR account created with sort key 014 
(Purchase Order) so at the time of 

1. Goods receipt Purchase order with item no will 
automatically filled in assignment field. 

Inventory dr. 15000

GR/IR cr 15000.

In GR/IR account item Assignment would be 150000 10.

2. Invoice through MIRO will also feed Purchase Order with 
item no in assignment field. 

GR/IR dr . 15000
Tax dr. 5000
Vendot cr. 20000

In GR/IR account item Assignment would be 150000 10.

Now your entry is over. There are large number of such 
entries posted in the period for the GR/IR account.
So, manual clearing becomes very tedious for GR/IR clearing 
account. In order to avoid that Automatic Clearing program 
is configured in OB74, where you give field ZUONR i.e. 
assignment in first criterion. So, line items with same 
assignment and amount will be cleared automatically upon 
F.13 transaction.