Using Oracle merge statement to merge specific rows from a group - sql

Question

Using Oracle database 19c, I'm trying to figure out how to merge only the rows with the most recent date in table1 into table2. If a new row with a matching tab1_id is later added to table1, it should update the row with the matching tab1_id the next time the merge statement is run.
CREATE TABLE table1 (
tab1_id NUMBER(2)
, log_date DATE
, group_name VARCHAR2(10)
, text2 VARCHAR2(10)
, text3 VARCHAR2(10)
, CONSTRAINT pk_tab1 PRIMARY KEY (tab1_id)
);
INSERT INTO table1 VALUES (1, '10-FEB-21', 'group1', 'textrow1', 'textrow1');
INSERT INTO table1 VALUES (2, '09-JAN-21', 'group1', 'textrow2', 'textrow2');
INSERT INTO table1 VALUES (3, '09-MAR-21', 'group1', 'textrow3', 'textrow3');
INSERT INTO table1 VALUES (4, '08-MAR-21', 'group2', 'textrow4', 'textrow4');
INSERT INTO table1 VALUES (5, '08-JAN-21', 'group2', 'textrow5', 'textrow5');
INSERT INTO table1 VALUES (6, '10-FEB-21', 'group2', 'textrow6', 'textrow6');
INSERT INTO table1 VALUES (7, '10-MAR-21', 'group3', 'textrow7', 'textrow7');
INSERT INTO table1 VALUES (8, '05-JAN-21', 'group3', 'textrow8', 'textrow8');
INSERT INTO table1 VALUES (9, '05-FEB-21', 'group3', 'textrow9', 'textrow9');
COMMIT;
CREATE TABLE table2 (
tab2_id NUMBER(2)
, tab1_id NUMBER(2) UNIQUE NOT NULL
, log_date DATE
, group_name VARCHAR2(10)
, text2 VARCHAR2(10)
, text3 VARCHAR2(10)
, CONSTRAINT pk_tab2 PRIMARY KEY (tab2_id)
);
CREATE SEQUENCE seq_table2_id MINVALUE 1 MAXVALUE 99 INCREMENT BY 1 START WITH 1 NOCACHE ORDER NOCYCLE;
These rows should merge into TABLE2 because they contain the most recent date in the log_date column.
edit-(Results should be something like this, ignoring the tab2_id column generated from a sequence.)
TAB2_ID TAB1_ID LOG_DATE GROUP_NAME TEXT2 TEXT3
---------- ---------- --------- ---------- ---------- ----------
1 3 09-MAR-21 group1 textrow3 textrow3
2 4 08-MAR-21 group2 textrow4 textrow4
3 7 10-MAR-21 group3 textrow7 textrow7
Update: based on Caius' comments, I got this to work:
MERGE INTO table2 t2
USING(
WITH T1_TO_MERGE AS (
SELECT
row_number() OVER(
PARTITION BY group_name
ORDER BY log_date DESC
) row_num,
tab1_id,
log_date,
group_name,
text2,
text3
FROM
table1
)
SELECT * FROM T1_TO_MERGE WHERE row_num = 1
) t1
ON(t2.group_name = t1.group_name)
WHEN MATCHED THEN UPDATE
SET t2.tab1_id = t1.tab1_id,
t2.log_date = t1.log_date,
t2.text2 = t1.text2,
t2.text3 = t1.text3
WHEN NOT MATCHED THEN
INSERT(
t2.tab2_id,
t2.tab1_id,
t2.log_date,
t2.group_name,
t2.text2,
t2.text3)
VALUES
(seq_table2_id.NEXTVAL,
t1.tab1_id,
t1.log_date,
t1.group_name,
t1.text2,
t1.text3);
COMMIT;