What is cardinality in Databases?

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 are also optional participation conditions to the above (where a row in one table doesn’t have to relate to the other table at all).

See Wikipedia on Cardinality (data modelling).

When talking about database query optimization, cardinality refers to the data in a column of a table, specifically how many unique values are in it. This statistic helps with planning queries and optimizing the execution plans.

See Wikipedia on Cardinality (SQL statements).

Related Posts:

  1. File extension .DB – What kind of database is it exactly?
  2. Difference between associative entity and associative relationship attribute?
  3. What’s the difference between identifying and non-identifying relationships?
  4. How to update multiple columns in single update statement in DB2
  5. Can I have multiple primary keys in a single table?
  6. “If not” condition statement in python
  7. How can I sort a dictionary by key?
  8. What does ERR_SPDY_PROTOCOL_ERROR mean in nginx?
  9. Time Complexity of Prims Algorithm?
  10. Ping – Request timed out
  11. How do I remove version tracking from a project cloned from git?
  12. What’s the difference between & and && in MATLAB?
  13. azure error 502 – Web server received an invalid response while acting as a gateway or proxy server
  14. What is a Ray ID (Cloudflare)?
  15. How do I get a list of built-in data sets in R?
  16. Tool for drawing parse trees?
  17. R dates “origin” must be supplied
  18. retrieve data from db and display it in table in php .. see this code whats wrong with it?
  19. What is difference between SQLite and SQL
  20. Simulate CREATE DATABASE IF NOT EXISTS for PostgreSQL?
  21. The name ‘InitializeComponent’ does not exist in the current context
  22. WPDB Insert or if exists Update
  23. What’s a good strategy for planning WordPress DB growth?
  24. How to check if image is already stored in a site’s post database? (network)
  25. WordPress database error: [Query was empty] [closed]
  26. Login in WordPress using external database data
  27. Shared Members between two different wordpress installations with different databases
  28. What is the fastest way to generate a unique id number when registering a user
  29. How to write Hebrew characters?
  30. Is there any reason only 1 (my) IP would be added to this table using $wpdn->insert?
  31. How to store data for posts/pages built with drag-n-drop builder?
  32. Error establishing a database connection – with Debug Data
  33. Finding the login page from database?
  34. When and why should I use $wpdb different return types?
  35. Bootstrapping WordPress MultiSite Outsite of WordPress – No $wpdb
  36. WordPress doesn’t show all posts in database
  37. Adding new row to wp_post table
  38. Extracting the post_id via the wp_insert_post action (external db query)
  39. How to determine what is generating large amount of database queries?
  40. How to interact with another wordpress install on same database?
  41. What is the proper way to validate and sanitize JSON response from REST API?
  42. batch UPDATE autoload value in wp_options table
  43. Is it possible to create Custom Post plug-in?
  44. How to modify post content?
  45. Saving into post_excerpt or post_content
  46. How to fix the disappearance of the “\” character when updating a post in the database
  47. How to select from two different tables to display orders list with custom column from other table
  48. Data storage for JS app using WP REST API
  49. Setup 3 Sites To Connect To 1 Database and Share Data
  50. How can I push local database changes to production, without impacting recent posts/pages that were published on production server?
  51. Emojis replaced by ‘?’ automatically
  52. Accessing two databases wordpress
  53. WSOD 3.9.1 – Tried Everything so far
  54. Can you refresh ONLY the wordpress adminbar and not the whole page?
  55. Array: What is this value based on?
  56. Sending posts from Python to WordPress
  57. Problem migrating to localhost
  58. Update all published posts at once
  59. Storing The Data Collected by Ninja Forms into Another (custom) Database [closed]
  60. Design problems when exporting remote database for local development
  61. How do you render posts from outside wordpress?
  62. custom post type: own database table structure and custom “new-post” interface
  63. Second ezSQL initialization for MSSQL
  64. Changing permalinks back to default ( ?p=123 )
  65. White Screen in Home Page
  66. Tracking Visitor LatLng with WordPress using JS, PHP. How to put data which was extract using JS into DB
  67. Continuous SQL query errors from outside source
  68. How to escape percentage sign(%) in sql query with $wpdb->prepare?
  69. Migrate Users From laravel to wordpress
  70. WordPress has been updated! Before we send you on your way, we have to update your database to the newest version
  71. how add more field to wp user and save it to database
  72. code that I can run, or a plug in to show what sql tables something pulls information from
  73. How do I cleanup my database with data that is no longer being used?
  74. Customized Essay Writing Service
  75. Malware in old website – how to migrate?
  76. Relational / Associate tables using native WordPress functionality
  77. How to display $wpdb->insert_id; value on redirected page
  78. HyperDB failover Delay
  79. Should I Use only wpdb Class to Write Custom Queries?
  80. Database Name Change
  81. custom post type for custom talbe
  82. Weird characters in title if it contain “ ”
  83. Where To Find bb_profile_data(); In bbPress?
  84. Host does not allow remote connection, so how do I transfer data to my WordPress site?
  85. MySQL Engine vs. Charset
  86. Bulk set Post Title as Tag where Tag is Empty Function
  87. Display total count of products in orders of a specific order status
  88. Cant Connect to Database
  89. The Joel Test for system administrator jobs
  90. How do I rename a task in Task Scheduled on Windows Server 2008 R2
  91. How do I get the history of “apt-get install” on Ubuntu?
  92. Why does x86 represent 32bit when x64 represents 64bit? [closed]
  93. How to reload screenrc without restarting screen?
  94. How long before an s3 bucket can be created with same name after deletion?
  95. Software vs hardware RAID performance and cache usage
  96. How do high traffic sites service more than 65535 TCP connections?
  97. Using variables in Apache config files to reduce duplication?
  98. How to unify package installation tasks in ansible?
  99. Private IP address in public DNS
  100. Can’t insert into a database wordpress

Leave a Comment