U. Dayal. Of nests and trees: A unified approach to processing queries that contain nested subqueries, aggregates, and quantifiers. In VLDB, pages 197--208, 1987.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....the query plan ahead of the user while waiting for the next DOM traversal step, we do not consider such speculative execution in this paper. 4 The Decorrelation Plan Space Decorrelation has been studied in the context of generating equivalent executions for correlated SQL queries in [6, 11, 15, 24]. In all previous work of which we are aware, plans are decorrelated when possible on the heuristic assumption that the decorrelated execution can be optimized better. On the contrary in ROLEX, when the navigation profile indicates that a node will seldom be visited, correlated execution may be ....

U. Dayal. Of nests and trees: A unified approach to processing queries that contain nested subqueries, aggregates, and quantifiers. In Proc. of Int'l Conf. on Very Large Data Bases, 1987.

....the query plan ahead of the user while waiting for the next DOM traversal step, we do not consider such speculative execution in this paper. 4 The Decorrelation Plan Space Decorrelation has been studied in the context of generating equivalent executions for correlated SQL queries in [6, 11, 15, 24]. In all previous work of which we are aware, plans are decorrelated when possible on the heuristic assumption that the decorrelated execution can be optimized better. On the contrary in ROLEX, when the navigation profile indicates that a node will seldom be visited, correlated execution may be ....

U. Dayal. Of nests and trees: A unified approach to processing queries that contain nested subqueries, aggregates, and quantifiers. In Proc. of Int'l Conf. on Very Large Data Bases, 1987.

....alternative algebra plans for universally quantified queries. Dayal [Day83] proposed the graft operator which bears some resemblance with a binary grouping (that we used as one evaluation technique) except that tree scheme occurrences are used as a representation of (intermediate) results. Later, [Day87] proposed the G Join, G Aggr and G Restr. The G Join replaces the graft operator and a sequence of G Aggr and G Restr replaces the previously used prune operator. GL87] treated queries with quantification as a special case of nested queries. The quantifiers exists and not exists are replaced by ....

U. Dayal. Of nests and trees: A unified approach to processing queries that contain nested subqueries. In Proc. of the Conf. on Very Large Data Bases (VLDB), pages 197--208, Brighton, England, 1987.

....the merge join is used. The inner relation or hash table for classic joins is selected as the largest one fitting in memory [14] The inner relation for semijoins is the one not retained in the output. The inner relation of an antijoin or outerjoin is determined by the operator s semantics [14] [2] and cannot be changed. For restrictions, we consider two algorithms, one used when the input relation comes sorted on the restriction attribute and one used otherwise. For projections, we consider an (M 1) way merge sort method [14] where M is the memory size in pages. The optimizer introduces ....

....depth of the move, indicating the number of nodes with which J will be swapped . for downward moves only: the child with which J is swapped in each individual swap, i.e. left or right child Outerjoins are excluded from JOIN node selection, because they do not always commute with normal joins [2]. If swapping of an outerjoin occurs during ROLL, the move 1. For reasons of simplicity, t n min is the time of sequential execution, so that parallelism can be introduced independently later on. Fig. 1. Dispersion of the duration of an optimization run. SPILIOPOULOU et al. PARALLEL ....

U. Dayal, "Of Nests and Trees: A Unified Approach to Processing Queries that Contain Nested Subqueries, Aggregates, and Quantifiers, " Proc. Int'l Conf. Very Large Databases, pp. 197--208, Brighton, England, 1987.

.... SQL2 compatible extensions for outerjoins are currently available in Sybase, NonStop SQL of Tandem, SSQL of ShareBase, and ORACLE SQL [Dav91, HM92] The operator is also used to represent algebraically some loop constructs of Daplex [Shi81] and to flatten nested SQL queries with Count aggregates [Day87, Mur89]. Unfortunately, it is known that outerjoins are neither commutative nor associative, in general. For this reason, a query graph in which edges indicate an operator (join or outerjoin) in addition to match predicates, is not an unambiguous representation of a Outerjoin Join (O J) query. ....

....definition, and take the union of the join R 1 p . R 2 and the antijoin R 1 p R 2 . But it seems reasonable to expect common work in the computation of joins and antijoins so, instead of computing them separately, it has been suggested to modify join algorithms to compute outerjoin directly [Day87]. We summarize next two basic implementation ideas that have been proposed [RR84, GL92, PMC93] and then extend them to join disjunctions. Simultaneous computation of join and antijoin. Since there are no common tuples in the join R 1 . R 2 and null padded antijoin R 1 R 2 , computing their ....

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U. Dayal. Of nests and trees: A unified approach to processing queries that contain nested subqueries, aggregates, and quantifiers. In Proceedings of the Thirteenth International Conference on Very Large Databases, Brighton, pages 197--208, 1987.

....set of types belonging to the set SourceSchema, denoting all the types found in the data sources, are treated as source nodes of a graph. For the rest of the types, we can derive an SQL expression by using existing view reduction algorithms, such as [33] corrected with the results of [19, 44, 45] [14, 11, 41, 48, 36]. Our algorithm is applicable to graphs of activities that do not involve updates. In most cases, an update operation can be considered as the combination of insertions and deletions or as the application of the appropriate function to the relevant attributes. The results of the application of ....

U. Dayal. Of Nests and Trees: A unified approach to processing queries that contain nested subqueries, aggregates and quantifiers. In Proc. 13 th Intl. Conf. on Very Large Data Bases (VLDB), pp. 197-208, Brighton, UK, (1987).

....and project operators Documents.document d Scan d.section s Scan D Join s.title t Scan D Join groupBy d, OpExists: E G Agg D Join t2 contains Web Select d.title t2 Scan E = true Select t Project Fig. 8. Lorel Plan for Query Q5 as well as a generalized aggregate operator [17]. The d join is a dependent join operator, sometimes called functional or implicit join. Its right input contains a free variable that is bound in the left input. Hence, the evaluation of the right input of a d join depends on the left input. The generalized aggregate operator performs a group by ....

U. Dayal. Of nests and trees: A unified approach to processing queries that contain nested subqueries, aggregates, and quantifiers. In VLDB, pages 197--208, 1987.

....flat relations. In particular, we show that containment is decidable for queries with arbitrary nesting of aggregation with uninterpreted aggregate functions as long as we do not perform joins or selections on aggregated columns. Previous work on optimization of queries with aggregation (e.g. [Day87, CS94, LMS94, RSSS94, LM96]) has focussed on providing transformation rules that can be applied to queries and conserve equivalence. However, equivalence and containment tests were not considered. Finite Model Theory Our containment algorithm for complex objects is based on a procedure for checking simulation on ....

Umesh Dayal. Of nests and trees: A unified approach to processing queries that contain nested subqueries, aggregates, and quantifiers. In Proceedings of VLDB-87, pages pages 197--208, 1987.

....efficiently. However, there exist some major differences between nested queries and joins that are, as stated in [12] the creation of duplicates and the way empty tables are handled. Indeed, these differences are at the bottom of most of the bugs subsequently detected in the original algorithms [10, 17, 6, 8, 11, 12]. To solve them and among other techniques, 8, 11] introduced outer joins. While these algebraic operators are a nice solution to some of the above problems, they raise new issues. If a sequence of join operations can easily be reordered, joins and outer joins do not commute that easily and one ....

....nested queries and joins that are, as stated in [12] the creation of duplicates and the way empty tables are handled. Indeed, these differences are at the bottom of most of the bugs subsequently detected in the original algorithms [10, 17, 6, 8, 11, 12] To solve them and among other techniques, [8, 11] introduced outer joins. While these algebraic operators are a nice solution to some of the above problems, they raise new issues. If a sequence of join operations can easily be reordered, joins and outer joins do not commute that easily and one has to find new ways of dealing with multi layered ....

[Article contains additional citation context not shown here]

U. Dayal. Of nests and trees: A unified approach to processing queries that contain nested subqueries, aggregates, and quantifiers. In VLDB, pages 197--208, 1987.

....to the function next then return pointers to qualifying tuples. A tuple qualifies if it is in a qualifying bucket or if the predicate applied to the tuples yields true. The pseudo code of SMA Scan is given in Figure 6. 3. 3 SMA GAggr The SMA GAggr operator computes the GAggr operator of Dayal [4] in the presence of SMAs. The GAggr operator performs a grouping together with the computation of aggregates. The SMA GAggr uses some SMAs called selection SMAs for selecting qualifying buckets and tuples. Hence, it encompasses the SMA Scan operator. However, more aggregates the aggregate ....

U. Dayal. Of nests and trees: A unified approach to processing queries that contain nested subqueries, aggregates, and quantifiers. In VLDB, pages 197--208, 1987.

....Another line of work has proceeded in an orthogonal direction, introducing execution plans which correspond to alternative structures of nesting. In particular, these approaches consider the possibilities of merging query blocks, denesting queries, and commuting aggregation blocks with joins [Day87, GW87, Kim82, Mur92, PHH92, YL94, HG94]. In this paper we propose an approach which unifies and generalizes the approaches mentioned above. We apply the selection propagation idea to certain data dependencies that are implicit in aggregation blocks. Propagation of SQL predicates [MFPR90a, MFPR90b, MPR90, LMS94] is a special case of ....

....dependencies that are implicit in aggregation blocks. Propagation of SQL predicates [MFPR90a, MFPR90b, MPR90, LMS94] is a special case of propagation of these dependencies. At the same time, propagating these 1 dependencies can produce execution plans with alternative nesting structure, as in [Day87, GW87, Kim82, Mur92, PHH92, YL94, HG94]. In addition to expressing in a common framework previously proposed query transformations which seemed unrelated, our approach incorporates naturally general data dependencies that may be given in the database schema. It extends transformations which commute joins with aggregation operators and ....

[Article contains additional citation context not shown here]

U. Dayal. Of nests and trees: a unified approach to processing queries that contain nested subqueries, aggregates, and quantifiers. In VLDB 1987.

....In spite of the acknowledged importance of such transformations, few systems have expanded upon these early transformation designs. Kim [Kim82] originally studied the question of when quantified subqueries could be replaced by joins (or anti joins) Ganski and Wong [GW87] and Dayal [Day87] did additional work on eliminating nested subqueries. These papers recognize the importance of merging of subqueries. Kim82, GW87] also deal with subqueries containing aggregation. We have reported our set of rules that deal with such subqueries in [MFPR90a, MPR90, MFPR90b] Ganski s paper ....

....such subqueries. As noted above, converting a subquery to a table expression (and hence a member of a join) increases possible orders of join execution. It may also allow for additional merging, if the subquery is another SELECT box. This rule is the QGM equivalent of a rule proven correct in [Day87] 5 We do not prove its correctness here, but an intuition of 5 The exact rule is Semijoin(R; S; J) Delta Project(Join if ( in a SELECT box there is a quantifier of type E forming a Boolean factor AND ( head.distinct = TRUE OR body.distinct = PERMIT OR one tuple condition) f set ....

[Article contains additional citation context not shown here]

Umeshwar Dayal. Of Nests and Trees: A Unified Approach to Processing Queries that Contain Nested Subqueries, Aggregates, and Quantifiers. In Proc. 13th International Conference on Very Large Data Bases, pages 197--208, Brighton, September 1987.

....and aggregation operations along the query tree, and push down these operations when an MVPP is generated by merging common join operations. Pulling up select and project operations are straight forward based on relational algebra or calculus. Some rewrite rules have been previously given in [10]. As for pushing down transformations after an MVPP is generated by merging common join operations, we have the following rules: ffl pushing down select operations: if there is more than one query sharing a join operation, and these queries have different select conditions on the attributes of ....

U. Dayal. Of nests and trees: A unified approach to processing queries that contain nested subqueries, aggregates, and quantifiers. In VLDB, 1987.

....3 Multiset (bag) has been proposed as an additional type constructor in order to formally deal with duplicates in relations. Since relational DBMSs typically do not guarantee the set property (duplicate elimination) of tables, a correct formalization has to use the concept of a multiset [34, 32, 128, 61]. Also, if SQL s aggregate operations shall be formalized, multisets are necessary. Alternatively, or in addition, one can introduce lists to cope with ordering (for example in order to express the physical storage sequence of tuples, to formalize the ORDER BY clause of SQL, or as a conceptual ....

U. Dayal. Of nests and trees: A unified approach to processing queries that contain nested subqueries, aggregates, and quantifiers. In Proc. Int. Conf. on Very Large Databases, pages 197--208, Brighton, September 1987. Morgan Kaufmann, Los Altos, Ca.

.... optimizers focus on queries involving the Select, Project and Join operators (see [Ull89] for a discussion of the theory upon which such strategies are based) Further work in relational optimization looked at extending optimization to include other operators, for example aggregators [Kim82, Day87] Optimization results have also been extended to include more expressive models, such as nested [S 89, Kor88] and network models [RR85, R 83] Object oriented databases are extensible systems which support (among other features) abstract data types, type inheritance (subtyping) methods ....

Umeshwar Dayal. Of Nests and Trees: A Unified Approach to Processing Queries That Contain Nested Subqueries, Aggregates, and Quantifiers. In Proceedings of the 13th VLDB Conference, pages 197--208, 1987.

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U. Dayal. Of nests and trees: A unified approach to processing queries that contain nested subqueries, aggregates, and quantifiers. In VLDB, pages 197--208, 1987.

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U. Dayal. Of nests and trees: A unified approach to processing queries that contain nested subqueries, aggregates, and quantifiers. In VLDB, pages 197--208, 1987.

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U. Dayal. Of nests and trees: A unified approach to processing queries that contain nested subqueries, aggregates, and quantifiers. In VLDB, pages 197--208, 1987.

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U. Dayal. Of Nests and Trees: A Unified approach to Processing Queries That Contain Nested Subqueries, Aggregates, and Quantifiers. In VLDB, 1987.

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U. Dayal. Of nests and trees: A unified approach to processing queries that contain nested subqueries, aggregates, and quantifiers. In VLDB, pages 197--208, 1987.

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U. Dayal. Of nests and trees: A unified approach to processing queries that contain nested subqueries, aggregates, and quantifiers. In VLDB, pages 197--208, 1987.

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U. Dayal. Of nests and trees: A unified approach to processing queries that contain nested subqueries, aggregates, and quantifiers. In VLDB, pages 197--208, 1987.

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U. Dayal. Of nests and trees: A unified approach to processing queries that contain nested subqueries, aggregates, and quantifiers. In VLDB, pages 197--208, 1987.

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U. Dayal. Of nests and trees: A unified approach to processing queries that contain nested subqueries, aggregates, and quantifiers. In VLDB, pages 197--208, 1987.

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U. Dayal. Of Nests and Trees: A unified approach to processing queries that contain nested subqueries, aggregates and quantifiers. In 13 th VLDB Conference, 1987.

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