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In SQL (Structured Query Language), the term cardinality refers to the uniqueness of data values contained in a particular column (attribute) of a database table. The lower the cardinality, the more duplicated elements in a column. Thus, a column with the lowest possible cardinality would have the same value for every row.
In computer science, the count-distinct problem [1] (also known in applied mathematics as the cardinality estimation problem) is the problem of finding the number of distinct elements in a data stream with repeated elements. This is a well-known problem with numerous applications.
Oracle implements hints by using specially-crafted comments in the query that begin with a + symbol, thus not affecting SQL compatibility. [2] EDB Postgres Advanced Server (a proprietary version of PostgreSQL from EnterpriseDB) offers hints compatible with those of Oracle. [3] [4] Microsoft SQL Server offers hints via the OPTION keyword [5]
Probabilistic cardinality estimators, such as the HyperLogLog algorithm, use significantly less memory than this, but can only approximate the cardinality. The HyperLogLog algorithm is able to estimate cardinalities of > 10 9 with a typical accuracy (standard error) of 2%, using 1.5 kB of memory. [1]
Microsoft SQL Server (Structured Query Language) 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 the Internet).
The Twilight Zone creator Rod Serling would have turned 100 on Dec. 25, 2024. To commemorate the anniversary, Rod’s daughters, Jodi and Anne, are looking back on some of their most meaningful ...
Programs calling a database that accords to the SQL standard receive an indication of the success or failure of the call. This return code - which is called SQLSTATE - consists of 5 bytes.
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