{"id":11382,"date":"2022-09-27T04:56:32","date_gmt":"2022-09-26T23:26:32","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-whats-wrong-with-this-sql\/"},"modified":"2022-09-27T04:56:32","modified_gmt":"2022-09-26T23:26:32","slug":"solved-whats-wrong-with-this-sql","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-whats-wrong-with-this-sql\/","title":{"rendered":"[Solved] What’s wrong with this SQL?"},"content":{"rendered":"

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SELECT\n      COALESCE(s.state, c.state) AS state\n    , COALESCE(s.city, c.city) AS city\n    , COALESCE(s.Suppliers, 0) AS Suppliers\n    , COALESCE(c.Consumers, 0) AS Consumers\nFROM (\n      SELECT\n            Tb_Supplier.State\n          , Tb_Supplier.City\n          , COUNT(Tb_Supplier.Name) AS Suppliers\n      FROM Tb_Supplier\n      GROUP BY\n            Tb_Supplier.City\n          , Tb_Supplier.State\n) AS s\n      FULL OUTER JOIN (\n            SELECT\n                  Tb_Consumer.State\n                , Tb_Consumer.City\n                , COUNT(Tb_Consumer.Name) AS Consumers\n            FROM Tb_Consumer\n            GROUP BY\n                  Tb_Consumer.City\n                , Tb_Consumer.State\n      ) AS c ON s.state = c.state\n                  AND s.city = c.city\n<\/code><\/pre>\n
The query above uses what I assume are “master tables” for Suppliers and Consumers, so rows in each should unique define a Supplier or Consumer. Hence count(distinct...)<\/code> is not required in the above approach. A full outer join<\/code> is used because there may be suppliers in state\/city with no matching consumers and vice-versa. Due to this coalesce<\/code> is used in the final select clause to deal with possible NULLs coming from either the supplier or consumer side.<\/p>\n
Why you should stop using commas between tables:<\/strong><\/p>\n
-- Accidental Cross Join? (Cartesian Product)\n-- or is it Deliberate\nselect * from table_one, table_two\n<\/code><\/pre>\n
In the above example each row<\/strong> of table_one is multiplied by all the rows<\/strong> of table_two. So, if both tables had 100 rows, the result is 100*100 = 10,000 rows. Did I want 10,000 rows?<\/p>\n
You have no idea if I wanted it or not, it could be deliberate or just an accident.<\/p>\n
select * from table_one CROSS JOIN table_two\n<\/code><\/pre>\n
But now I DO know that the cross join is deliberate.<\/p>\n
Look back at your original question.<\/p>\n
FROM \n    Tb_Supplier, Tb_Consumer\nGROUP BY \n    Tb_Supplier.City, Tb_Supplier.State, Tb_Consumer.City, Tb_Consumer.State\u200b\n<\/code><\/pre>\n
If you had 1,000 Suppliers and 100,000 consumers how many rows did you create in that from clause? (1,000 * 100,000 = 100,000,000) I’m quite certain that was accidental, and that is why you should stop using commas between tables in the from clause.<\/em><\/p>\n<\/p><\/div>\n
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solved What’s wrong with this SQL? <\/p>\n","protected":false},"excerpt":{"rendered":"
[ad_1] SELECT COALESCE(s.state, c.state) AS state , COALESCE(s.city, c.city) AS city , COALESCE(s.Suppliers, 0) AS Suppliers , COALESCE(c.Consumers, 0) AS Consumers FROM ( SELECT Tb_Supplier.State , Tb_Supplier.City , COUNT(Tb_Supplier.Name) AS Suppliers FROM Tb_Supplier GROUP BY Tb_Supplier.City , Tb_Supplier.State ) AS s FULL OUTER JOIN ( SELECT Tb_Consumer.State , Tb_Consumer.City , COUNT(Tb_Consumer.Name) AS Consumers FROM Tb_Consumer … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[341,500,1009],"class_list":["post-11382","post","type-post","status-publish","format-standard","hentry","category-solved","tag-sql","tag-sql-server","tag-tsql"],"yoast_head":"\n[Solved] What's wrong with this SQL? - JassWeb<\/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:\/\/jassweb.com\/solved\/solved-whats-wrong-with-this-sql\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] What's wrong with this SQL? - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] SELECT COALESCE(s.state, c.state) AS state , COALESCE(s.city, c.city) AS city , COALESCE(s.Suppliers, 0) AS Suppliers , COALESCE(c.Consumers, 0) AS Consumers FROM ( SELECT Tb_Supplier.State , Tb_Supplier.City , COUNT(Tb_Supplier.Name) AS Suppliers FROM Tb_Supplier GROUP BY Tb_Supplier.City , Tb_Supplier.State ) AS s FULL OUTER JOIN ( SELECT Tb_Consumer.State , Tb_Consumer.City , COUNT(Tb_Consumer.Name) AS Consumers FROM Tb_Consumer ... 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