Abstract: In some examples, the database system maintains metadata for a plurality of data objects, the metadata containing ranges of values of an attribute for the plurality of data objects, where the ranges of values of the attribute comprise a respective range of values of the attribute for each corresponding data object of the plurality of data objects. The database system generates a data structure tracking quantities of ranges of values of the attribute that have a specified relationship with respect to corresponding different values of the attribute. The database system receives a database query comprising a predicate specifying a condition on a given value of the attribute, and computes, for the database query, a selectivity of filtering based on the metadata, the selectivity computed based on the data structure.

Abstract: In some examples, the database system maintains metadata for a plurality of data objects, the metadata containing ranges of values of an attribute for the plurality of data objects, where the ranges of values of the attribute comprise a respective range of values of the attribute for each corresponding data object of the plurality of data objects. The database system generates a data structure tracking quantities of ranges of values of the attribute that have a specified relationship with respect to corresponding different values of the attribute. The database system receives a database query comprising a predicate specifying a condition on a given value of the attribute, and computes, for the database query, a selectivity of filtering based on the metadata, the selectivity computed based on the data structure.

Abstract: A parallel database system processes database queries invoking a user defined function (UDF). The database query is specified in a database query language, for example, the structured query language (SQL) and the UDF is specified in a programming language different from the database query language, for example, C/C++. The UDF may include multiple phases. The parallel database system generates optimized code for the UDF. The parallel database system includes a leader node and a plurality of compute nodes. The database query processes one or more database tables such that each compute node processes a slice of each database table. The leader node sets up a global context structure and provides it to each compute node. The global context may be shared across multiple executions of the query. The UDF may be used for efficient execution of extraction, transformation, and loading of data from external systems.

Abstract: A parallel database system processes database queries invoking a user defined function (UDF). The database query is specified in a database query language, for example, the structured query language (SQL) and the UDF is specified in a programming language different from the database query language, for example, C/C++. The UDF may include multiple phases. The parallel database system generates optimized code for the UDF. The parallel database system includes a leader node and a plurality of compute nodes. The database query processes one or more database tables such that each compute node processes a slice of each database table. The leader node sets up a global context structure and provides it to each compute node. The global context may be shared across multiple executions of the query. The UDF may be used for efficient execution of extraction, transformation, and loading of data from external systems.

Abstract: A database system rewrites database queries based on rewrite constraints specification. The rewrite constraints specification provides directives to the database system to generate temporary tables for storing intermediate results of database queries and rewrite the corresponding database queries in terms of the temporary tables. The subqueries for matching the rewrite constraints specification may be specified in various ways. For example, the rewrite constraints specification may identify the subqueries by using one or more aliases. The rewrite constraints specification may specify a list of tables such that all database queries that join the database tables specified in the rewrite constraints specification are determined to match. The optimizer is able to optimize the rewritten database queries better by getting a better estimate for the statistics describing the temporary tables.

Abstract: A database system allows users to specify plan constraint specification that limit choices of execution plans considered by an optimizer of the database system for optimizing database queries. The plan constraint specification specifies attributes of execution plans. The plan constraint specification may identify tables/intermediate results that the plan constraint is applicable to using table names or aliases. The database system applies the plan constraint specification to database queries that match the tables/aliases specified in the plan constraint specification. The database system limits the choice of execution plans evaluated for a database query to execution plans satisfying the attributes specified in an applicable plan constraint specification. The plan constraint specification may specify distribution of a table, a join order for tables, the join mechanism, cardinality of a table or intermediate result, and so on.

Abstract: A system and/or method are implemented to process queries to a database. In particular, the processing of queries to the database is enhanced by enhancing the determination of join orders of tables implicated in queries. Join orders between relatively large numbers of tables are determined by dividing the set of tables to be ordered into a plurality of subsets of tables, and ordering the individual subsets of tables.

Abstract: A database system optimizes database queries that comprise subqueries. The database system factors out computation from two or more subqueries to a reusable subquery. The reusable subquery returns a result set. The subqueries are rewritten to use the result set and the database query modified to use the rewritten subqueries. The modified database query performs efficiently since the result set is computed only once for each subquery that uses the reusable query. The database system also composes nested subqueries that compute aggregate values. The database system identifies an inner subquery nested within an outer subquery, each subquery computing an aggregate value. The database system determines a new aggregate function corresponding to a composition of aggregate functions of the inner and the outer queries. The database system determines a composed query using the inner query with the outer query. The composed query uses the new aggregate function.

Abstract: A database system optimizes database queries that comprise subqueries. The database system factors out computation from two or more subqueries to a reusable subquery. The reusable subquery returns a result set. The subqueries are rewritten to use the result set and the database query modified to use the rewritten subqueries. The modified database query performs efficiently since the result set is computed only once for each subquery that uses the reusable query. The database system also composes nested subqueries that compute aggregate values. The database system identifies an inner subquery nested within an outer subquery, each subquery computing an aggregate value. The database system determines a new aggregate function corresponding to a composition of aggregate functions of the inner and the outer queries. The database system determines a composed query using the inner query with the outer query. The composed query uses the new aggregate function.

Abstract: A database system optimizes database queries that comprise subqueries. The database system factors out computation from two or more subqueries to a reusable subquery. The reusable subquery returns a result set. The subqueries are rewritten to use the result set and the database query modified to use the rewritten subqueries. The modified database query performs efficiently since the result set is computed only once for each subquery that uses the reusable query. The database system also composes nested subqueries that compute aggregate values. The database system identifies an inner subquery nested within an outer subquery, each subquery computing an aggregate value. The database system determines a new aggregate function corresponding to a composition of aggregate functions of the inner and the outer queries. The database system determines a composed query using the inner query with the outer query. The composed query uses the new aggregate function.

Abstract: A database system allows users to specify plan constraint specification that limit choices of execution plans considered by an optimizer of the database system for optimizing database queries. The plan constraint specification specifies attributes of execution plans. The plan constraint specification may identify tables/intermediate results that the plan constraint is applicable to using table names or aliases. The database system applies the plan constraint specification to database queries that match the tables/aliases specified in the plan constraint specification. The database system limits the choice of execution plans evaluated for a database query to execution plans satisfying the attributes specified in an applicable plan constraint specification. The plan constraint specification may specify distribution of a table, a join order for tables, the join mechanism, cardinality of a table or intermediate result, and so on.

Abstract: A database system rewrites database queries based on rewrite constraints specification. The rewrite constraints specification provides directives to the database system to generate temporary tables for storing intermediate results of database queries and rewrite the corresponding database queries in terms of the temporary tables. The subqueries for matching the rewrite constraints specification may be specified in various ways. For example, the rewrite constraints specification may identify the subqueries by using one or more aliases. The rewrite constraints specification may specify a list of tables such that all database queries that join the database tables specified in the rewrite constraints specification are determined to match. The optimizer is able to optimize the rewritten database queries better by getting a better estimate for the statistics describing the temporary tables.

Abstract: A system and/or method are implemented to process queries to a database. In particular, the processing of queries to the database is enhanced by enhancing the determination of join orders of tables implicated in queries. Join orders between relatively large numbers of tables are determined by dividing the set of tables to be ordered into a plurality of subsets of tables, and ordering the individual subsets of tables.

Abstract: A system and/or method are implemented to process queries to a database. In particular, the processing of queries to the database is enhanced by enhancing the determination of join orders of tables implicated in queries. Join orders between relatively large numbers of tables are determined by dividing the set of tables to be ordered into a plurality of subsets of tables, and ordering the individual subsets of tables.

Abstract: A system and/or method are implemented to process queries to a database. In particular, the processing of queries to the database is enhanced by enhancing the determination of join orders of tables implicated in queries. Join orders between relatively large numbers of tables are determined by dividing the set of tables to be ordered into a plurality of subsets of tables, and ordering the individual subsets of tables.

Abstract: A system and/or method are implemented to process queries to a database. In particular, the processing of queries to the database is enhanced by enhancing the determination of join orders of tables implicated in queries. Join orders between relatively large numbers of tables are determined by dividing the set of tables to be ordered into a plurality of subsets of tables, and ordering the individual subsets of tables.

Abstract: A system and/or method are implemented to process queries to a database. In particular, the processing of queries to the database is enhanced by enhancing the determination of join orders of tables implicated in queries. Join orders between relatively large numbers of tables are determined by dividing the set of tables to be ordered into a plurality of subsets of tables, and ordering the individual subsets of tables.