cardinality

I keep coming across these terms: high cardinality and low cardinality in Cassandra . I don't understand what exactly they mean. what effects they have on queries and what is preferred. Please explain with example since that will be be easy to follow. The cardinality of X is nothing more than the number of elements that compose X. In Cassandra the partition key cardinality is very important for partitioning data. Since the partition key is responsible for the distribution of the data across the cluster, choosing a low cardinality key might lead to a situation in which your data are not

As answered in this question: Cardinality in PostgreSQL , cardinality is enfforced using constraints . Cardinality rules define the allowable counts of the relationships – one-to-many, many-to-many, etc. Many-to-many is achieved using join-tables and one-to-many using FOREIGN KEY. But how can one implement one-to-one_or_many (one-to-1+) relationship. Which is same as to ask: How can I enforce minimum cardinality in PostgreSQL? A practical situation would be where one needs to store say address (or telephone number) which MUST be provided (but can be more that one) by the person (say user or

Is it possible to determine the cardinality of a c++ enum class : enum class Example { A, B, C, D, E }; I tried to use sizeof , however, it returns the size of an enum element. sizeof(Example); // Returns 4 (on my architecture) Is there a standard way to get the cardinality (5 in my example) ? Not directly, but you could use the following trick: enum class Example { A, B, C, D, E, Count }; Then the cardinality is available as (int)Example::Count . Of course, this only works nicely if you let values of the enum be automatically assigned, starting from 0. If that's not the case, you can manually

I have been searching all over the internet but I couldn't seem to find an answer that I can understand. So kindly, if somebody could explain to me with the help of examples what is cardinality in databases? Thank you. A source of confusion may be the use of the word in two different contexts - data modelling and database query optimization. In data modelling terms, cardinality is how one table relates to another. 1-1 (one row in table A relates to one row in tableB) 1-Many (one row in table A relates to many rows in tableB) Many-Many (Many rows in table A relate to many rows in tableB) There

For example, if I have a table with a city and a state column, what is the best way to use the index? Obviously city will have the highest cardinality, so should I put that column first in the index, should I put state or doesn't it matter much? MySQL composite index lookups must take place in the order in which the columns are defined within the index. Since you want MySQL to be able to discriminate between records by performing as few comparisons as possible, with all other things being equal you will benefit most from from a composite index in which the columns are ordered from highest- to

I have a table which has duplicate indexes(same column is indexed twice ( BTREE )) but surprisingly cardinality is different. Why this is happening. 'ACCENTURE_PASSIVE_CANDIDATES', '1', 'LD_INDEX', '1', 'LOCATION_DISTANCE', 'A', '37876', NULL, NULL, 'YES', 'BTREE', '', '' 'ACCENTURE_PASSIVE_CANDIDATES', '1', 'RS_INDEX', '1', 'RELEVANCY_SCORE', 'A', '21996', NULL, NULL, 'YES', 'BTREE', '', '' 'ACCENTURE_PASSIVE_CANDIDATES', '1', 'score_index', '1', 'RELEVANCY_SCORE', 'A', '146566', NULL, NULL, 'YES', 'BTREE', '', '' 'ACCENTURE_PASSIVE_CANDIDATES', '1', 'location_index', '1', 'LOCATION_DISTANCE'

I think I am going crazy! I have followed the various tutorials for Owl and Protege and still cannot figure out the answer. Use case is simple. I have defined a class called ‘Person’. I have defined a data property called hasFirstName. I have added a ‘subclass of’ restriction to Person like this : ‘hasFirstName exactly 1 string’. I have also added an individual called Alex of type Person, and have not added the hasFirstName property. I expect the reasoner to complain as I have specified the cardinality of 1, and asserted that Alex is a Person, but have not added the property value to Alex