Technique for processing query in database management system

1. A method for processing a query in a database management system (DBMS), the method comprising:

receiving a main query including a subquery;

identifying an indication to independently manage a processing result of the subquery in the received main query by parsing the received main query—the indication including storing type information for the processing result of the subquery;

determining a storing type for independently storing the processing result of the subquery based on the indication, wherein when the determined storing type is determined to be an external storing type, an external file storage in which the processing result of the subquery is to be stored in a file form is determined, an external table connected to the determined external file storage in a memory is generated, meta data for reading a file stored in the external file storage is generated, and the generated meta data is stored in the generated external table;

processing the received main query and the subquery; and

storing the processing result of the subquery independently from a processing result of the received main query during the processing of the received main query according to the determined storing type.

2. The method of claim 1 , wherein the received main query includes a WITH clause, and the subquery is included in the WITH clause.

3. The method of claim 2 , wherein the indication is included in a statement expressed outside the subquery in the WITH clause.

4. The method of claim 2 , further comprising:

generating information for requesting whether the subquery is to move to the WITH clause when it is determined that the subquery included in the received main query is not included in the WITH clause or when the received main query including the subquery does not have the WITH clause by parsing the received main query.

5. The method of claim 1 , wherein the indication further includes external file storage position information for the processing result of the subquery and file name information for the processing result of the subquery, and the external file storage is determined based on the external file storage position information and the meta data is generated based on the external file storage position information and the file name information.

6. The method of claim 1 , further comprising:

when the determined storing type is determined to be an internal storing type,

generating in a memory a read-only temporary table in which the processing result of the subquery is to be stored in a table form.

7. The method of claim 6 , wherein the indication further includes at least one of internal file storage position information for the processing result of the subquery and table name information for the processing result of the subquery.

8. The method of claim 1 , further comprising:

in order to permit the processing result of the subquery to be reused,

generating a meta table for storing at least one of storage position information of the subquery, structured query language (SQL) statement information of the subquery, time information when the processing result of the subquery is generated, and snapshot information for the processing result of the subquery.

9. The method of claim 1 , wherein the storing of the processing result of the subquery independently from the processing result for the received main query includes:

generating, in a memory, a meta table for independently storing an intermediate result for the processing of the subquery, and

storing the intermediate result for the processing of the subquery in the generated meta table.

10. A non-transitory computer-readable recording medium including a computer program configured to perform operations for query processing in a database management system (DBMS) when the computer program is executed by one or more processors, the operations comprising:

receiving a main query including a subquery;

identifying an indication to independently manage a processing result of the subquery in the received main query by parsing the received main query—the indication including storing type information for the processing result of the subquery;

determining a storing type for independently storing the processing result of the subquery based on the indication, wherein when the determined storing type is determined to be an external storing type, an external file storage in which the processing result of the subquery is to be stored in a file form is determined, an external table connected to the determined external file storage in a memory is generated, meta data for reading a file stored in the external file storage is generated, and the generated meta data is stored in the generated external table;

processing the received main query and the subquery; and

storing the processing result of the subquery independently from a processing result of the received main query during the processing of the received main query according to the determined storing type.

11. A server for processing a query in a database management system (DBMS), the server comprising:

a communicator configured to receive a main query including a subquery;

a query parser configured to identify an indication to independently manage a processing result of the subquery in the received main query by parsing the received main query—the indication including storing type information for the processing result of the subquery;

a storing type determiner configured to determine a storing type for independently storing the processing result of the subquery based on the indication, wherein when the determined storing type is determined to be an external storing type, an external file storage in which the processing result of the subquery is to be stored in a file form is determined, an external table connected to the determined external file storage in a memory is generated, meta data for reading a file stored in the external file storage is generated, and the generated meta data is stored in the generated external table;

an operation executor configured to process the received main query and the subquery; and

a storer configured to store the processing result of the subquery independently from a processing result of the received main query during the processing of the received main query according to the determined storing type.