NVL should NOT be replaced by COALESCE in Oracle but stay NVL. Their behavior are not the same in term of data type conversion.

[Hal-H2Apps]

Fully reproducible code snippet
In oracle DB :

CREATE TABLE TEST1 (COL1 INT, COL2 VARCHAR2(10))
INSERT INTO TEST1 VALUES (1,'2')

SELECT * FROM TEST1 WHERE NVL(COL2, 1) <> COL1

--> COL1 COL2
1 2

SELECT * FROM TEST1 WHERE COALESCE(COL2, 1) <> COL1

--> ORA-00932: inconsistent datatypes: expected : CHAR ; got : NUMBER

As we can see, NVL does NOT care about the type, COALESCE does. Therefore both function are not identical.

In python with sqlglot:
sqlQuery: str = """ SELECT * FROM TEST1 WHERE NVL(COL2, 1) <> COL1"""
sql = sqlglot.parse_one(sql=sqlQuery, read='oracle')
print(sql.sql(dialect='oracle'))
-> SELECT * FROM TEST1 WHERE COALESCE(COL2, 1) <> COL1
I should have NVL and not COALESCE. These 2 functions are not identical.

Official Documentation
Please include links to official SQL documentation related to your issue.

https://docs.oracle.com/en/database/oracle/oracle-database/19/sqlrf/NVL.html
"If expr1 is character data, then Oracle Database converts expr2 to the data type of expr1 before comparing them and returns VARCHAR2 in the character set of expr1."