如果你说的是set的cardinality，那么cardinality就是集合中元素的个数。那么，你可能会问：直接叫count不...
This Oracle tutorial explains how to use the Oracle / PLSQL CARDINALITY function with syntax and examples. The Oracle / PLSQL CARDINALITY function returns the number of elements in a nested table.
Themany-to-many (M:N) relationshipmeans that many rows in one table are related to many rows in a second table. In other words, many instances in one entity correlate with many instances in a second entity. For example, a student can sign up for many classes, and a class can have m...
With the release of SQL Server 2014, there were several good reasons to overhaul what was basically the CE as introduced 15 years ago. Our goals in SQL Server Development certainly were to avoid issues we so far experienced over the past 15 years and which were not fixable witho...
@graham.hitchings - A unique column will have high cardinality too based on the link in the QOTD. It states: An example of a data table column with high-cardinality would be a USERS table with a column named USER_ID. This column would contain unique values of 1-n. Each time a new ...
SQL Server uses constant folding with the following types of expressions: Arithmetic expressions, such as 1+1, 5/3*2, that contain only constants. Logical expressions, such as 1=1 and 1>2 AND 3>4, that contain only constants. Built-in functions that are considered foldable by SQL Server...
We will follow up with a later blog post when that paper is released. Additionally, Juergen Thomas has posted an overview of the feature on "Running SAP on SQL Server blog". In this blog, we will provide a quick overview about controlling the SQL Server 2014 feature, guidelines on ...
scenario better, as it will assume that rows do exist, which results in a better estimate and often a better plan choice. We can see this with a quick example (provided to me by Yi Fang from the SQL Server product team) against the FactCurrencyRate table in the AdventureWorks2012 data...
For example, for an equality join between two tables, we use the base tables histograms to estimate the join selectivity, and then factor in the predicates selectivity.Use Query Store to assess the CE versionStarting with SQL Server 2016 (13.x), the Query Store is a...
Some of the more modern time series databases are built for many series. InfluxDB is an example. They’ve put a lot of work into handling tons of series, and they have quite a bit in their documentation abouthow InfluxDB deals with high cardinality. ...