table_id (PK) number;
table_1_id number;
table_2_id number;

table_id number;
table_1_id number;
table_2_id number;
table_key number;
table_key_data varchar2(15);

table_1_id table_2_id table_id table_key table_key_data
1          123        12345    1         1111
1          123        12345    2         ABC

12345
    23456
    34567
..plus hundreds/thousands more

table_1_id table_2_id table_id table_key table_key_data
1          123        12345    1         1111
1          123        12345    2         ABC
1          123        23456    1         1111
1          123        23456    2         ABC
1          123        34567    1         1111
1          123        34567    2         ABC
...plus remaining hundreds/thousands more.

INSERT INTO TABLE_B (SELECT 1,123,TABLE_A.TABLE_ID, 1 for the first record and 2 for second record, CASE WHEN table_key = 1 THEN '1111' WHEN table_key = 2 THEN '1111111' END FROM TABLE_A WHERE TABLE_A.TABLE_ID NOT IN (SELECT table_id FROM TABLE_B)