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ClickHouse was designed for OLAP queries. [5] ClickHouse performs well when: It works with a small number of tables that contain a large number of columns. Queries use a large number of rows extracted from the DB, but only a small subset of columns. Queries are relatively rare (usually around 100 requests per second per server).
OLAP server XML for Analysis OLE DB for OLAP MDX Stored procedures Custom functions SQL LINQ [19] Visualization JSON REST API; Apache Doris No No No No Yes [20] Yes No Superset, Redash, Metabase, Tableau, Qlik, Pivot, PowerBI Yes Yes Apache Druid: No No No No Yes Druid SQL No Superset, Pivot, Redash Yes Yes Apache Kylin: Yes No Yes No Yes Yes
A hierarchical query is a type of SQL query that handles hierarchical model data. They are special cases of more general recursive fixpoint queries, which compute transitive closures. In standard SQL:1999 hierarchical queries are implemented by way of recursive common table expressions (CTEs).
Join order: Because it joins functions commutatively and associatively, the order in which the system joins tables does not change the final result set of the query. However, join-order could have an enormous impact on the cost of the join operation, so choosing the best join order becomes very important.
An ORDER BY clause in SQL specifies that a SQL SELECT statement returns a result set with the rows being sorted by the values of one or more columns. The sort criteria does not have to be included in the result set (restrictions apply for SELECT DISTINCT, GROUP BY, UNION [DISTINCT], EXCEPT [DISTINCT] and INTERSECT [DISTINCT].)
A query language, also known as data query language or database query language (DQL), is a computer language used to make queries in databases and information systems. In database systems, query languages rely on strict theory to retrieve information. [1] A well known example is the Structured Query Language (SQL).
Microsoft SQL Server (Structured Query Language) (often prounced "sequel") is a proprietary relational database management system developed by Microsoft.As a database server, it is a software product with the primary function of storing and retrieving data as requested by other software applications—which may run either on the same computer or on another computer across a network (including ...
In other databases, alternatives to express the same query (other queries that return the same results) can be tried. Some query tools can generate embedded hints in the query, for use by the optimizer. Some databases - like Oracle - provide a plan table for query tuning. This plan table will return the cost and time for executing a query.