I have a mysql
table (scho_id
,school_name
,school_views
).
I was looking for a mysql
query to get rank
of schools on the basis of school_views
.
I found this solution on stackoverflow.
SET @points := -1, @num := 0;
SELECT scho_id
, school_views
, @num := if(@points = school_views, @num, @num + 1) as school_rank
, @points := school_info.school_views as dummy
FROM school_info
ORDER BY school_views desc, scho_id asc;
This solved my problem but I notice a new operator :=
in this query. I am curious to know the meaning and uses of this operator.
In MySQL, :=
is an assignment operator:
SELECT @foo := 'bar'; // variable 'foo' now has value 'bar'
return value: 'bar'
while =
is an equality test:
SELECT @foo = 'hi mom'; // does variable 'foo' have the value 'hi mom';
return value: false ('bar' == 'hi mom' -> false)
Note that you CAN do both equality testing AND assignment with set
queries:
SET @foo = 'bar' = 'baz';
which will cause @foo
to be assigned false
, the boolean result of 'bar' = 'baz'
. It executes as the following:
SET @foo = ('bar' = 'baz');
SET @foo = false;