Problems with USING ALL CLIENTS

[lorenzo_masiello1]

Dear SAP-Community

I have an abap-sql, that selects data on two clients (100 and 700). Some data is in client 100 and some other in client 700.
With the old known CLIENT SPECIFIED a SELECT with CLIENT is possible. 

The following code functions, but returns a warning saying I should use USING ALL CLIENTS instead of client specified:

lv_mandt_100 = '100'.
lv_mandt_700 = '700'.

SELECT
FROM ekko AS ekko_100
LEFT OUTER JOIN t024 AS t024_100
   ON
    t024_100~mandt = @LV_mandt_100 AND
     t024_100~ekgrp = ekko_100~ekgrp
LEFT OUTER JOIN ekko AS ekko_700
   ON
       ekko_700~mandt = @LV_mandt_700 AND
       ekko_100~mandt = @LV_mandt_100 AND
       ekko_100~externalreferenceid = ekko_700~ebeln
  LEFT OUTER JOIN ekpo AS ekpo_100
     ON
       ekko_100~mandt = @LV_mandt_100 AND
       ekpo_100~mandt = @LV_mandt_100 AND
       ekko_100~ebeln = ekpo_100~ebeln
  CLIENT SPECIFIED
FIELDS
  ekko_100~ebeln AS ebeln_100,
  ekko_100~ekgrp AS ekgrp_100,
  t024_100~eknam AS eknam_100,
  ekko_700~ebeln AS ebeln_700,
  ekpo_100~ebelp AS ebelp_100,
  ekpo_100~konnr AS ekpo_100_konnr,
  ekpo_100~txz01 AS ekpo_100_txz01
WHERE
  ekko_100~mandt      = @LV_mandt_100
ORDER BY
  ekko_100~ebeln,
  ekpo_100~ebelp
INTO TABLE @DATA(mt_output)
BYPASSING BUFFER.

If I replace the CLIENT SPECIFIED with USING ALL CLIENTS I get an error, that I am not allowed to use field "MANDT" in an ON-constraint.

lv_mandt_100 = '100'.
lv_mandt_700 = '700'.

SELECT
FROM ekko AS ekko_100
LEFT OUTER JOIN t024 AS t024_100
   ON
     t024_100~mandt = @LV_mandt_100 AND
     t024_100~ekgrp = ekko_100~ekgrp
LEFT OUTER JOIN ekko AS ekko_700
   ON
       ekko_700~mandt = @LV_mandt_700 AND
       ekko_100~mandt = @LV_mandt_100 AND
       ekko_100~externalreferenceid = ekko_700~ebeln

  LEFT OUTER JOIN ekpo AS ekpo_100
     ON
       ekko_100~mandt = @LV_mandt_100 AND
       ekpo_100~mandt = @LV_mandt_100 AND
       ekko_100~ebeln = ekpo_100~ebeln
  USING ALL CLIENTS "<- instead of CLIENT SPECIFIED belongig to the warning
FIELDS
  ekko_100~ebeln AS ebeln_100,
  ekko_100~ekgrp AS ekgrp_100,
  t024_100~eknam AS eknam_100,
  ekko_700~ebeln AS ebeln_700,
  ekpo_100~ebelp AS ebelp_100,
  ekpo_100~konnr AS ekpo_100_konnr,
  ekpo_100~txz01 AS ekpo_100_txz01
WHERE
  ekko_100~mandt      = @LV_mandt_100
ORDER BY
  ekko_100~ebeln,
  ekpo_100~ebelp
INTO TABLE @DATA(mt_output)
BYPASSING BUFFER.

Documentation for USING ALL CLIENTS is here: https://help.sap.com/doc/abapdocu_latest_index_htm/latest/en-US/abapselect_client.htm 

Belongig the documentation it's not possible to use USING ALL CLIENTS for a single join. But in the above code I use it for the whole FROM/JOIN.

So, my question is, how should I change the abap code to use USING ALL CLIENTS instead of CLIENT SPECIFIED?

And my other question is, if I use the CLIENT SPECIFIED, will the code in future not function anymore?

Best regards
Lorenzo