SELECT COUNT(*)AS cnt FROM info AS i LEFT JOIN user AS u ON i.grpid=u.grpid WHERE i.type=1 GROUP BY i.grpidthe data with no results queried in this way will not be displayed. What can I do if I want the data without results to be displayed as 0?
SELECT COUNT(*)AS cnt FROM info AS i LEFT JOIN user AS u ON i.grpid=u.grpid WHERE i.type=1 GROUP BY i.grpidthe data with no results queried in this way will not be displayed. What can I do if I want the data without results to be displayed as 0?
laxative, I don't see where your sql will be empty.
left link, where Filter left table field, groupby is also the left table, the record to which count
Filter is taken is sure count is not 0 either
then use ifnull (col1,0) to handle null values
I guess you need to change the join order of info and user
you can use MYSQL IF () Function
SELECT IF(SELECT COUNT(*)AS cnt FROM info AS i LEFT JOIN user AS u ON i.grpid=u.grpid WHERE i.type=1 GROUP BY i.grpid) = 0 , "0", SELECT COUNT(*)AS cnt FROM info AS i LEFT JOIN user AS u ON i.grpid=u.grpid WHERE i.type=1 GROUP BY i.grpid) AS cnt;
the following is the Syntax of IF
IF(condition, value_if_true, value_if_false)
you can use mysql's if operation if you want the data with no result to be 0. Of course, it is recommended that it be done by the program.
use if to set a default value of 0 for the field you want it to be 0
is changed to from user first and then left join info table.
SELECT COUNT (i.id) AS cnt FROM user AS u LEFT JOIN info AS i ON i.grpid=u.grpid WHERE i.type=1 GROUP BY i.grpid
the reason is that info does not necessarily have records in the user table.
when querying, it will first find out all the records in the user table, and then find the total number of info records corresponding to the user.
according to the way you write it, if a user has no info record, there is nothing to display
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