Custom SQL Queries
Applicable only to SQL-based connectors, a data source using a connector that supports custom SQL queries can use an SQL query to select fields from the table. The custom SQL statement can be specified on the Custom SQL area of the Source Creation tab after selecting the Custom SQL option.
Custom SQL queries are a powerful tool for performing complex data queries. However, be careful when creating custom SQL queries because it is easy to define a heavy query or a query that may overwhelm your database. Use this feature carefully.
In SQL-based sources, Composer typically wraps the query with select * from. For example, suppose the original query is this:
select count(*), someField from myCollection GROUP By someField
The resulting query that Composer uses is this:
select * from (select count(*), someField from myCollection GROUP By someField)
Support for this feature by Composer connectors is shown in the following table.
Key:Y - Supported; N - Not Supported; N/A - not applicable