ABAP join Syntax: 

The ABAP JOIN syntax follows Open SQL standards for combining data from multiple SAP tables.

Select <data base table 1> ~ <field 1> <data base table 1> ~ <field 2> ——-
<data base table 2> ~ <field 1> <data base table 2> ~ <field 2> ——–
<data base table 3> ~ <field 1> <data base table 3> ~ <field 2> ——–
into table <internal table > from <database table1> inner join <database table 2 > on
<data base table 1> ~ <field > = <data base table 2> ~ <field > inner join <data base table 3> on
<data base table 2> ~ <field> = <data base table 3> ~ <field>…………..Where <condition>.

Objects:    Based on the given vendor numbers, to display the vendor numbers,vendor name, purchasing document numbers, document dates, item numbers, quantity, unit of measurements & net price.

Data v1 type lfa1-lifnr.
select-options s_lifnr for v1.

Types: Begin of ty_final,
LIFNR TYPE LFA1-LIFNR,
NAME1 TYPE LFA1-NAME1,
EBELN TYPE EKKO-EBELN,
BEDAT TYPE EKKO-BEDAT,
EBELP TYPE EKPO-EBELP,
MENGE TYPE EKPO-MENGE,
MEINS TYPE EKPO-MEINS,
NETPR TYPE EKPO-NETPR,
end of ty_final.
Data: wa_final type ty_final,
it_final type table of ty_final.
Select LFA1~LIFNR LFA1~NAME1 EKKO~EBELN EKKO~BEDAT EKPO~EBELP EKPO~MENGE EKPO~MEINS EKPO~NETPR into table it_final from LFA1 inner join EKKO on LFA1~LIFNR = EKKO~LIFNR inner join EKPO on EKKO~EBELN = EKPO~EBELN where LFA1~LIFNR in S_lifnr.
Loop at it_final into wa_final.
Write:/ wa_final-lifnr, wa_final-name1, wa_final-ebeln, wa_final-bedat, wa_final-ebelp,
wa_final-menge, wa_final-meins, wa_final-netpr.
Endloop.