Expression pushdown optimization for querying in federated database system

A non-transitory computer-readable storage medium storing computer-executable instructions that, when executed by a processor, cause the processor to perform operations comprising:

• receiving a target query specified in a common query language, the target query including an expression specifying a target feature;
• and
• for each data source of a plurality of data sources,
• accessing a respective converter for converting features of the common query language to corresponding features of a data source query language for the data source, wherein the respective converter is configured for a common type and a common operator of the common query language;
• when the data source supports the target feature specified in the expression of the target query,
• converting, by the respective converter, the target feature specified in the expression to the corresponding feature of the data source query language;
• submitting, to the data source, a first query including a converted expression with the corresponding feature of the data source query language;
• and
• obtaining query results based on the first query that includes the converted expression;
• and
• when the data source does not support the target feature specified in the expression of the target query,
• generating a second query that does not include the expression or a converted version of the expression;
• submitting the second query to the data source such that query result data is selected from the data source without being filtered based on the expression;
• receiving, from the data source, the query result data;
• and
• generating a first query result by filtering the query result data using the expression.

A computing system for query optimization in a federated database system, the computing system comprising:

• a processor;
• and
• a computer-readable storage medium storing computer-executable instructions that, when executed by the processor, cause the processor to perform operations comprising:
• receiving a target query specified in a common query language, the target query including an expression specifying a target feature;
• and
• for each data source of a plurality of data sources,
• accessing a respective converter for converting features of the common query language to corresponding features of a data source query language for the data source, wherein the respective converter is configured for a common type and a common operator of the common query language;
• when the data source supports the target feature specified in the expression of the target query,
• converting, by the respective converter, the target feature specified in the expression to the corresponding feature of the data source query language;
• and
• submitting, to the data source, a first query including a converted expression with the corresponding feature of the data source query language;
• and
• obtaining query results based on the first query that includes the converted expression;
• and
• when the data source does not support the target feature specified in the expression of the target query,
• generating a second query that does not include the expression or a converted version of the expression;
• submitting the second query to the data source such that query result data is selected from the data source without being filtered based on the expression;
• receiving, from the data source, the query result data;
• and
• generating a first query result by filtering the query result data using the expression.