Methods and apparatus for parallel execution in a database system. In one implementation, a database system includes: one or more data storage facilities for use in storing data composing records in tables of a database; one or more processing modules configured to manage the data stored in the data-storage facilities, where at least one processing module is configured to: open a memory pipe for a pipe operator, run a first thread to execute a pipe source operation providing output data to the memory pipe, and run a second thread to execute a pipe sink operation receiving input data from the memory pipe while the first thread is running; and a database management component configured to parse an expression and recognize a pipe operator and a pipe source operation and a pipe sink operation for the pipe operator.