Abstract: A database engine includes one or more computing devices, each having one or more processors and memory. The memory stores programs configured for execution by the processors. The database engine receives a database query from a client, and parses the database query to build a query operator tree. The query operator tree includes a plurality of query operators. The database engine performs one or more optimization passes on the query operator tree, including a deduplication optimization pass, to form an optimized execution plan. The deduplication optimization pass includes determining that a first query operator is equivalent to a second query operator during a traversal of the query operator tree, and replacing the second query operator with a link to reuse results from the first query operator. The database engine executes the optimized execution plan to retrieve a result set from the database and returns the result set to the client.

Abstract: A database engine receives a database query that specifies retrieving data from a data source. The database engine parses the query to build an operator tree that includes a TableScan operator configured to scan a table from the data source to produce outputs corresponding to a single data field from the table, and includes a GroupBy operator that groups rows of the table according to the data field. The database engine generates and executes code corresponding to the operator tree to retrieve a result set. When the TableScan operator is a child of the GroupBy operator and the outputs are independent of duplicate input rows from the table, execution of the TableScan operator comprises, for each storage block of rows from the table: determining a storage compression scheme for encoding the data field and, for certain encodings, using the encoding to produce the outputs without duplication of rows.

Abstract: A database engine receives a human-readable database query that includes a plurality of conditional expressions. The database engine parses the database query to build an operator tree that includes a subtree corresponding to each of the conditional expressions. The database engine identifies a subexpression that appears in two or more of the conditional expressions. The subexpression is executed conditionally. The database engine hoists the subexpression outside of the conditional expression so that it is executed unconditionally. The database engine modifies the operator tree to specify computation of a value for the subexpression a first time and to reuse the computed value when the subexpression is subsequently encountered. The database engine executes the modified operator tree to form a result set corresponding to the database query, thereby evaluating the subexpression only a single time for each row of input data and returns the result set.

Abstract: A database engine includes one or more computing devices, each having one or more processors and memory. The memory stores programs configured for execution by the processors. The database engine receives a database query from a client, and parses the database query to build a query operator tree. The query operator tree includes a plurality of query operators. The database engine performs one or more optimization passes on the query operator tree, including a deduplication optimization pass, to form an optimized execution plan. The deduplication optimization pass includes determining that a first query operator is equivalent to a second query operator during a traversal of the query operator tree, and replacing the second query operator with a link to reuse results from the first query operator. The database engine executes the optimized execution plan to retrieve a result set from the database and returns the result set to the client.

Abstract: A database engine receives a database query from a client. The database engine parses the database query to build a query operator tree that includes a plurality of query operators. The database engine performs one or more optimization passes on the query operator tree, including a deduplication optimization pass, to form an optimized execution plan. The deduplication optimization pass includes: creating a list of query operators via a first traversal of the query operator tree, determining a first query operator that is equivalent to a second query operator, based on a hash map, via a second traversal of the query operator tree, and substituting, via a third traversal of the query operator tree, the second query operator with a tree node that links to the first query operator. The database engine executes the optimized execution plan to retrieve a result set from the database, and returns the result set.

Abstract: A database engine receives a database query from a client. The database engine parses the database query to build a query operator tree that includes a plurality of query operators. The database engine performs one or more optimization passes on the query operator tree, including a deduplication optimization pass, to form an optimized execution plan. The deduplication optimization pass includes: creating a list of query operators via a first traversal of the query operator tree, determining a first query operator that is equivalent to a second query operator, based on a hash map, via a second traversal of the query operator tree, and substituting, via a third traversal of the query operator tree, the second query operator with a tree node that links to the first query operator. The database engine executes the optimized execution plan to retrieve a result set from the database, and returns the result set.