![]() ![]() INNER JOIN payments p ON s.user_id = p.student_idĪdditionally, if you'd want to show only the results that have open pending payments you could add a HAVING statement after the GROUP BY, such as HAVING u.pending_payments > 0īelow showing the query results. INNER JOIN students s ON u.id = s.user_id Try the following (untested, sorry, not in front of pc with editor on it) SELECT u.username, u.first_name, u.email, COUNT(p.is_paid) as pending_payments To show only results that match criteria, use an INNER JOIN statement.Īlso, you wish to COUNT(*) payments due by username, you should GROUP BY username I should think. A Left join gets done, even if parameters do not match in that table, because they might make up columns in another (joined) table. The fact that you receive "null" response is due to the LEFT JOIN statements. But since there is no matching row, it returns NULL. The server is free to select the valueĪgain: "The server is free to select the value from any row". Treating all rows as a single group, but the value selected for each If ONLY_FULL_GROUP_BY is not enabled, the query is processed by ![]() If the ONLY_FULL_GROUP_BY SQL mode is enabled, an error occurs: GROUP BY clause should be present that names those same columns. If you name columns to select in addition to the COUNT() value, a Note that this query is not SQL standard compliant, and in strict mode you will get an error, because username is selected without beeng listed in the GROUP BY clause. It is just how aggregate functions work (in MySQL), and you will see the same behavior with a simple example without joins like SELECT username, COUNT(*) This has nothing to do with the LEFT or any JOIN. SELECT ername, COUNT(payments.id) as pending_payments If username is not UNIQUE and you want to get one row for all users with the same username, you can use the HAVING clause instead of GROUP BY to "remove" the "empty" row. Note that you will get one row per user with that username. GROUP BY ername, users.first_name, users.email So use a GROUP BY clause, if you want an empty result: SELECT ername, users.first_name, users.email, ![]() (keep the behavior when user exists, but returns Empty set when does not exists, instead of a row will NULL values).Īggregate functions like COUNT(*) always generate one row if no GROUP BY clause is used. How can I modify my query to get the expected results? Instead, when the username does not exists, I want as result: When the username exists and there are 2 pending payments, it returns: | username | first_name | email | pending_payments |īut when the username does not exists, it returns: | username | first_name | email | pending_payments | When the username exists and there are not pending payments, it returns: | username | first_name | email | pending_payments | LEFT JOIN payments ON payments.student_id = students.id AND payments.is_paid = 0 And I have the following query: SELECT ername, users.first_name, users.email, ![]()
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