SQL Modules and Variable Expansion

The %sql cell magic serves two purposes:

• executing a SQL query statement immediately
• defining a SQL module for later execution

Variable substitution is done immediately in the first case using the IPython notebook execution environment.

In the second case what happens is a Python module is created and immediately imported, using the name supplied in the -m/--module argument. This module will have several variables defined in its namespace:

• _sql_module_arg_parser is a Python argparse argument parser that is created from any Python variable definitions at the start of the cell;
• _sql_module_main is the main query statement (datalab.data.SqlStatement object) to be executed for the cell;
• _sql_module_last is the last query statement defined in the cell; this is frequently the same as _sql_module_main
• for each SQL query that starts with a DEFINE QUERY \<name>\ prefix, `<name>' will be bound to that query statement