Passing Parameters with Pandas read_sql

Overview

The Pandas read_sql function allows you to execute SQL queries and retrieve data from a database. One of its features is the ability to pass parameters to the query.

Parameter Syntax

Params can be passed as a list, tuple, or dict. The exact syntax depends on the database driver being used. Here are some common examples:

• ? or %s: Placeholder for a single value
• :1 or :name: Named placeholder for a single value
• %(name)s: Named placeholder using the string.format syntax

Using a Dictionary with Named Arguments

One option for passing parameters is to use a dictionary. This is supported by most drivers, including PostgreSQL with the psycopg2 driver. The key-value pairs in the dictionary correspond to the named placeholders in the query.

Example

To demonstrate the named argument approach, let's consider the following SQL query:

select "Timestamp", "Value" from "MyTable"
where "Timestamp" BETWEEN :dstart AND :dfinish

Here's how you would pass parameters to this query using a dictionary:

params = {"dstart": datetime(2014, 6, 24, 16, 0), "dfinish": datetime(2014, 6, 24, 17, 0)}

df = psql.read_sql(
    "select \"Timestamp\",\"Value\" from \"MyTable\" where \"Timestamp\" BETWEEN %(dstart)s AND %(dfinish)s",
    db,
    params=params,
    index_col=["Timestamp"],
)

In this example, the params dictionary provides values for the named placeholders :dstart and :dfinish. The %(name)s syntax ensures that the values are inserted correctly into the query.