How to Pass Parameters to SQL Queries in Pandas\' read_sql()?

Passing Parameters in Pandas' read_sql with SQL Queries

Problem:

When working with Pandas' read_sql() method and SQL queries, users may encounter difficulties passing parameters to the query. While the documentation mentions the use of parameters as a list or tuple, some users find issues when attempting to use a dictionary format.

Solution:

According to the read_sql() documentation, parameters can indeed be passed as a dictionary. However, the syntax supported by the database driver used in the connection plays a crucial role.

For Psycopg2, the database driver commonly used when connecting to PostgreSQL, the named argument syntax is supported. In this case, the parameter names should be enclosed in double % signs and specified as a dictionary, as shown below:

<code class="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>

In this example, the %()s syntax is used to define the parameter placeholders in the SQL query. The corresponding values are then passed as a dictionary to the params argument of read_sql().

By utilizing the correct syntax for the database driver in use, users can successfully pass parameters to SQL queries when using Pandas' read_sql() method.

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