Oracle 11g Release 2

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CREATE TABLE tableA
    ("CUSTOMER_ID" int, "GEO_ID" int, "GEO" varchar2(10))
;

INSERT ALL 
    INTO tableA ("CUSTOMER_ID", "GEO_ID", "GEO")
         VALUES (1234567890, 3521, 'texas')
    INTO tableA ("CUSTOMER_ID", "GEO_ID", "GEO")
         VALUES (0987654321, 3624, 'dallas')
    INTO tableA ("CUSTOMER_ID", "GEO_ID", "GEO")
         VALUES (1597536842, 3121, 'mexicocity')
SELECT * FROM dual
;
3 rows affected


CREATE TABLE tableB
    ("GEO_ID" int, "CUSTOMER_ID" int)
;

INSERT ALL 
    INTO tableB ("GEO_ID", "CUSTOMER_ID")
         VALUES (8745, 1234567890)
    INTO tableB ("GEO_ID", "CUSTOMER_ID")
         VALUES (2145, 0987654321)
    INTO tableB ("GEO_ID", "CUSTOMER_ID")
         VALUES (3699, 1597536842)
SELECT * FROM dual
;
3 rows affected

update tablea a set 
    a.geo_id = (select geo_id from 
                      tableb b 
                      where a.customer_id = b.customer_id)
3 rows affected

select * from Tablea


CUSTOMER_ID
GEO_ID
GEO


1234567890
8745
texas

987654321
2145
dallas

1597536842
3699
mexicocity


MERGE INTO tablea a 
     using tableb b ON( a.customer_id = b.customer_id ) 
WHEN matched THEN 
  UPDATE SET a.geo_id = b.geo_id 
3 rows affected

select * from Tablea


CUSTOMER_ID
GEO_ID
GEO


1234567890
8745
texas

987654321
2145
dallas

1597536842
3699
mexicocity

CUSTOMER_ID	GEO_ID	GEO
1234567890	8745	texas
987654321	2145	dallas
1597536842	3699	mexicocity