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Query by Example (QBE) is a database query language for relational databases. It was devised by Moshé M. Zloof at IBM Research during the mid-1970s, in parallel to the development of SQL . [ 1 ] It is the first graphical query language, using visual tables where the user would enter commands, example elements and conditions.
The set of query plans examined is formed by examining the possible access paths (e.g., primary index access, secondary index access, full file scan) and various relational table join techniques (e.g., merge join, hash join, product join). The search space can become quite large depending on the complexity of the SQL query. There are two types ...
In a SQL database query, a correlated subquery (also known as a synchronized subquery) is a subquery (a query nested inside another query) that uses values from the outer query. This can have major impact on performance because the correlated subquery might get recomputed every time for each row of the outer query is processed.
In SQL implementations, joining on a predicate is usually called an inner join, and the on keyword allows one to specify the predicate used to filter the rows. It is important to note: forming the flattened Cartesian product then filtering the rows is conceptually correct, but an implementation would use more sophisticated data structures to ...
The query containment problem for conjunctive queries is also equivalent to the constraint satisfaction problem. [7] An important class of conjunctive queries that have polynomial-time combined complexity are the acyclic conjunctive queries. [8] The query evaluation, and thus query containment, is LOGCFL-complete and thus in polynomial time. [9]
The SQL specification defines what an "SQL schema" is; however, databases implement it differently. To compound this confusion the functionality can overlap with that of a parent database. An SQL schema is simply a namespace within a database; things within this namespace are addressed using the member operator dot ".". This seems to be a ...
Data modeling is supported as part of a complete modeling platform. 2000 ER/Studio: Embarcadero (acquired by IDERA) SMBs and enterprises Proprietary: Access, Snowflake, Microsoft Azure IBM Db2, Informix, Hitachi HiRDB, Firebird, Interbase, MySQL, MS SQL Server, Netezza, Oracle, PostgreSQL, Sybase, Teradata, Visual Foxpro and others via ODBC ...
While all Access data can migrate to SQL Server directly, some queries cannot migrate successfully. In some situations, you may need to translate VBA functions and user defined functions into T–SQL or .NET functions / procedures. Crosstab queries can be migrated to SQL Server using the PIVOT command.