Dask read_sql_query did not execute sql that I put in

Question

Hi all I'm new to Dask.

I faced an error when I tried using read_sql_query to get data from Oracle database.

Here is my python script:

con_str = "oracle+cx_oracle://{UserID}:{Password}@{Domain}/?service_name={Servicename}"

sql= " 
    column_a, column_b                                                 
    from 
        database.tablename  
    where 
        mydatetime >= to_date('1997-01-01 00:00:00','YYYY-MM-DD HH24:MI:SS')
"

from sqlalchemy.sql import select, text    
from dask.dataframe import read_sql_query

sa_query= select(text(sql))
ddf = read_sql_query(sql=sa_query, con=con, index_col="index", head_rows=5)

I refered this post: Reading an SQL query into a Dask DataFrame Remove "select" string from my query. And I got an cx_Oracle.DatabaseError with missing expression [SQL: SELECT FROM DUAL WHERE ROWNUM <= 5]

But I don't get it where the query came from.

Seem like it didn't execute the sql code I provided.

I'm not sure which part I did not config right.

*Note: using pandas.read_sql is ok , only fail when using dask.dataframe.read_sql_query