Specifying NULL columns when MySQL LEFT join returns specific values detailed _mysql

The COALESCE function can accept more than one argument and returns the first Non-null value of those arguments, or null if all the supplied arguments are null
The Ifnull function, like the COALESCE function, can only accept two parameters
The IF function accepts three parameters, which is similar to the ternary (?:) function, that is, the first argument is not null and is not 0 o'clock, the second argument is returned, or the third argument is returned

Copy Code code as follows:

SELECT A.*,coalesce (t.cous,0) as Count from Brand as a
Left JOIN (select Brandid as Bid,count (1) as cous to Shopbrand Group by Brandid) T on A.brandid=t.bid
Order by Count DESC LIMIT 0,20

The above syntax is to do a statistic, itself will return null, but empty words is not a good practice, so use coalesce to solve