(1) in ERP, use tcode SM30, view name: MATERIALID, configure an external long material number for material created in MM01：

in my example, it is AAAAA

Once saved, it will be saved in table MATERIALID as below:

(2) download it into CRM:

This is what I observed in tcode SMW01:

Question 1: why I insert an entry in Material Identification including a external material number and then the external number will disappear after I save it.

Answer:

There is a routine to convert the input/output of MATERIALID-MATNR_EXT

When I insert a value in MATERIALID-MATNR_EXT, the input value will be convert to another value according to rules in CONVERSION_EXIT_MATNL_INPUT. In my case, ENHANCEMENT MGV_CONV_EXIT_SAPLOMCV in FM CONVERSION_EXIT_MATNL_INPUT is switched off.

So When I insert aaaa, you can see the input is converted to null.

Question 2: Why I can see external long material number in se11 table Materialid, but cannot see data in view material identification ?

Answer:

The display of external long material number in view "material identification" is converted by routine:

But the ENHANCEMENT 8 MGV_CONV_EXIT_SAPLOMCV in CONVERSION_EXIT_MATNL_OUTPUT is still switched off which is same as in FM CONVERSION_EXIT_MATNL_INPUT. So we just can see null external long material number in view "material identification".

Debug the data extract FM CRS_MATERIAL_EXTRACT in ERP side:

Before extract data from table materialid, two condition must be met:

table mgv_tlmnr is used to activate long material number:

After activate long material number, one entry will generate in table mgv_tlmnr about time.