betodealmeida edited a comment on issue #13491:
URL: https://github.com/apache/superset/issues/13491#issuecomment-792057345
Since `FETCH_MANY` is inefficient, another way to solve the problem of
databases like Teradata and Firebird that use a syntax other than `LIMIT` is to
implement the `apply_limit_to_sql` method in the DB engine spec. The base
method (in `superset/db_engine_specs/base.py`) is:
```python
@classmethod
def apply_limit_to_sql(cls, sql: str, limit: int, database: "Database")
-> str:
"""
Alters the SQL statement to apply a LIMIT clause
:param sql: SQL query
:param limit: Maximum number of rows to be returned by the query
:param database: Database instance
:return: SQL query with limit clause
"""
# TODO: Fix circular import caused by importing Database
if cls.limit_method == LimitMethod.WRAP_SQL:
sql = sql.strip("\t\n ;")
qry = (
select("*")
.select_from(TextAsFrom(text(sql), ["*"]).alias("inner_qry"))
.limit(limit)
)
return database.compile_sqla_query(qry)
if cls.limit_method == LimitMethod.FORCE_LIMIT:
parsed_query = sql_parse.ParsedQuery(sql)
sql = parsed_query.set_or_update_query_limit(limit)
return sql
```
You could implement a custom method in
`superset/db_engine_specs/teradata.py` that applies the correct syntax for
Teradata.
This approach would be better than the one you have modifying
`superset/db_engine_specs/base.py`, `superset/sql_lab.py`, and
`superset/sql_parse.py`, since all the changes needed to support Teradata would
be self-contained in `db_engine_specs/teradata.py`.
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