MySQL实现排名并查询指定用户排名功能，并列排名功能
表结构：
CREATE TABLE test.testsort (
id int(11) NOT NULL AUTO_INCREMENT,
uid int(11) DEFAULT 0 COMMENT '用户id',
score decimal(10, 2) DEFAULT 0.00 COMMENT '分数',
PRIMARY KEY (id)
)
ENGINE = INNODB
AUTO_INCREMENT = 1
CHARACTER SET utf8
COLLATE utf8_general_ci
COMMENT = '测试排序'
ROW_FORMAT = DYNAMIC;
思路：可以先排序，再对结果进行编号；也可以先查询结果，再排序编号。
说明：
@rownum := @rownum + 1 中 := 是赋值的作用，这句话的意思是先执行@rownum + 1，然后把值赋给@rownum；
(SELECT @rownum := 0) r 这句话的意思是设置rownum字段的初始值为0，即编号从1开始。
实现排名：
方法一：
SELECT t.*, @rownum := @rownum + 1 AS rownum
FROM (SELECT @rownum := 0) r, (SELECT * FROM testsort ORDER BY score DESC) AS t;
方法二：
SELECT t.*, @rownum := @rownum + 1 AS rownum
FROM (SELECT @rownum := 0) r, testsort AS t
ORDER BY t.score DESC;
结果：
查看指定用户排名：
方法一：
SELECT b.* FROM
(
SELECT t.*, @rownum := @rownum + 1 AS rownum
FROM (SELECT @rownum := 0) r,
(SELECT * FROM testsort ORDER BY score DESC) AS t
) AS b WHERE b.uid = 222;
方法二:
SELECT b.* from
(
SELECT t.*, @rownum := @rownum + 1 AS rownum
FROM (SELECT @rownum := 0) r, testsort AS t
ORDER BY t.score DESC
) as b where b.uid = 222;
结果：
实现并列排名(相同分数排名相同)：
SELECT
obj.uid,
obj.score,
CASE
WHEN @rowtotal = obj.score THEN
@rownum
WHEN @rowtotal := obj.score THEN
@rownum :=@rownum + 1
WHEN @rowtotal = 0 THEN
@rownum :=@rownum + 1
END AS rownum
FROM
(
SELECT
uid,
score
FROM
testsort
ORDER BY
score DESC
) AS obj,
(SELECT @rownum := 0 ,@rowtotal := NULL) r
查询指定用户并列排名:
SELECT total.* FROM
(SELECT
obj.uid,
obj.score,
CASE
WHEN @rowtotal = obj.score THEN
@rownum
WHEN @rowtotal := obj.score THEN
@rownum :=@rownum + 1
WHEN @rowtotal = 0 THEN
@rownum :=@rownum + 1
END AS rownum
FROM
(
SELECT
uid,
score
FROM
testsort
ORDER BY
score DESC
) AS obj,
(SELECT @rownum := 0 ,@rowtotal := NULL) r) AS total WHERE total.uid = 222;
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