{"id":3578,"date":"2023-04-12T15:39:33","date_gmt":"2023-04-12T15:39:33","guid":{"rendered":"https:\/\/quebit.com\/askquebit\/exploring-the-sql-cartesian-join\/"},"modified":"2026-01-15T18:15:51","modified_gmt":"2026-01-15T18:15:51","slug":"exploring-the-sql-cartesian-join","status":"publish","type":"post","link":"https:\/\/quebit.com\/askquebit\/exploring-the-sql-cartesian-join\/","title":{"rendered":"What Is a SQL Cartesian Join and When Does It Occur in Queries?"},"content":{"rendered":"

Joins are an interesting and critical part of understanding and using the SQL language. One of the most curious is the Cartesian join<\/a>.<\/p>\n

Simply put, cartesian joins generate a \u201ccartesian product\u201d, which is defined as \u201c\u2026t<\/em>he product of two sets: the product of set X and set Y (is) the set that contains all ordered pairs (x, y) for which x belongs to X and y belongs to Y\u2026\u201d.<\/em><\/p>\n

SQL Server<\/strong><\/p>\n

In SQL Server, the cartesian product<\/strong> is really a cross-join which returns all the rows in all the tables listed in a query<\/em>:\u00a0 each<\/strong> row in the first table is paired with all the rows<\/strong> in the second table.\u00a0 This happens when there is no relationship defined between the two tables.<\/p>\n

An Example<\/strong><\/p>\n

To best understand this concept, consider the following example.<\/p>\n

In a new fast food restaurant, the manager is keen to assign the duty in which each employee is most efficient performing. A database has been created which contains the following three tables:<\/p>\n

C_Employee<\/strong> \u2013 holding the restaurant employees<\/p>\n

C_Duty<\/strong> \u2013 holding the duties<\/p>\n

C_Utilization<\/strong> \u2013 tracking employee utilization by duty<\/p>\n

Currently we have only 3 employees:<\/p>\n

\"\"<\/p>\n

And only 3 duties to be performed:<\/p>\n

\"\"<\/p>\n

Using a cartesian join, we can write the following query:<\/p>\n

Select EmployeeName<\/p>\n

,Duty<\/p>\n

from<\/p>\n

C_Employee, C_Duty<\/p>\n

When we run that query, we receive the expected results (the cartesian product):<\/p>\n

\"\"<\/p>\n

You can see that we have each duty assigned to each employee for a total of 9 rows (3 employees x 3 duties) returned.<\/p>\n

Taking this a step further, we know that in the 3rd<\/sup> table, calculated utilizations for each duty are being entered by Employee ID:<\/p>\n

\"\"<\/p>\n

So, if we introduce a subquery<\/a> into our original query:<\/p>\n

Select EmployeeName<\/p>\n

,Duty<\/p>\n

,(Select Utilization from C_Utilization where<\/p>\n

C_Employee.EmployeeID = C_Utilization.EmployeeID<\/p>\n

and C_Duty.DutyID = C_Utilization.DutyID) AS ‘UTILIZATION’<\/p>\n

from<\/p>\n

C_Employee, C_Duty<\/p>\n

order by EmployeeName, UTILIZATION DESC<\/p>\n

it will add some insight to our results in that we can easily identify which duty is perhaps best for each of our valued employees:<\/p>\n

\"\"<\/p>\n

Conclusion<\/strong><\/p>\n

So, a JOIN is a SQL\u00a0\u201cclause\u201d that is used to bring together rows from two or more SQL tables, based on a related column between them. The cartesian join is just one type of join. You can learn about all of different SQL joins here<\/a>, or look for my next post that explains the use of each type of join.<\/p>\n

I hope this little example helped in understanding how a cartesian join it works.<\/p>\n","protected":false},"excerpt":{"rendered":"

Joins are an interesting and critical part of understanding and using the SQL language. One of the most curious is the Cartesian join. Simply put, cartesian joins generate a \u201ccartesian product\u201d, which is defined as \u201c\u2026the product of two sets: the product of set X and set Y (is) the set that contains all ordered…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[27],"tags":[32],"class_list":["post-3578","post","type-post","status-publish","format-standard","hentry","category-quebit-value","tag-sql"],"acf":[],"yoast_head":"\nWhat Is a SQL Cartesian Join and When Does It Occur in Queries? - QueBIT<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/quebit.com\/askquebit\/exploring-the-sql-cartesian-join\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"What Is a SQL Cartesian Join and When Does It Occur in Queries? - QueBIT\" \/>\n<meta property=\"og:description\" content=\"Joins are an interesting and critical part of understanding and using the SQL language. One of the most curious is the Cartesian join. 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