How to Correctly Pass Named Parameters with Pandas `read_sql` to a PostgreSQL Database?

Use Pandas read_sql to pass SQL query parameters

Pandas provides the read_sql function for retrieving data from a SQL database. This function allows passing parameters to the SQL query, enabling dynamic querying. However, the method of passing parameters may differ.

The example uses the SQLAlchemy engine to connect to the PostgreSQL database. The query uses BETWEEN %s AND %s as a positional parameter and can work normally.

However, the question is whether it is possible to pass named parameters using a dictionary, such as :dstart and :dfinish. The Pandas documentation points out this possibility, but in practice it fails.

According to the read_sql documentation, the params parameter can accept a list, tuple, or dictionary. There are also various syntaxes for passing values ​​within the SQL query itself, including ?, :1, :name, %s, and %(name)s.

Crucially, the supported syntax depends on the database driver used. In this case, the driver is most likely psycopg2.

The psycopg2 documentation shows that named parameters are supported using the %(name)s style, rather than the :name style that was attempted. Therefore, the following code should work:

<code class="language-python">df = psql.read_sql(('select "Timestamp","Value" from "MyTable" '
                     'where "Timestamp" BETWEEN %(dstart)s AND %(dfinish)s'),
                   db,
                   params={"dstart": datetime(2014, 6, 24, 16, 0), "dfinish": datetime(2014, 6, 24, 17, 0)},
                   index_col=['Timestamp'])</code>

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