MySQL uses and implements ranking functions rank and deny_ Rank and row_ NUMBER

---

stay MYSQL Latest version MYSQL8 The ranking function has been supported RANK,DENSE_RANK and ROW_NUMBER. However, these functions are not supported in the ready version , It can only be achieved by itself . The implementation method mainly uses conditional judgment statements （CASE WHEN or IF） And adding temporary variables .

---

1. Ranking classification

1.1 difference RANK,DENSE_RANK and ROW_NUMBER

• RANK Juxtaposed jump rankings , Juxtaposition is the same value , The same value keeps the duplicate ranking , When you encounter the next different value , Jump to the total ranking .
• DENSE_RANK Side by side continuous sorting , Juxtaposition is the same value , The same value keeps the duplicate ranking , When you encounter the next different value , Still ranked by consecutive numbers .
• ROW_NUMBER Continuous ranking , Even if the same value , Still ranked by consecutive numbers .

The difference is shown in the picture ：

1.2 Group ranking

Rank the data after grouping , The difference is shown in the picture ：

2. Prepare the data

Create a score table , There are fields in it ： fraction score, Course no. course_id And student number student_id.
The implementation is as follows SQL sentence , Import data .

create table score(
  student_id varchar(10),
  course_id varchar(10),
  score decimal(18,1)
);
insert into score values('01' , '01' , 80);
insert into score values('01' , '02' , 90);
insert into score values('01' , '03' , 99);
insert into score values('02' , '01' , 70);
insert into score values('02' , '02' , 60);
insert into score values('02' , '03' , 80);
insert into score values('03' , '01' , 80);
insert into score values('03' , '02' , 80);
insert into score values('03' , '03' , 80);
insert into score values('04' , '01' , 50);
insert into score values('04' , '02' , 30);
insert into score values('04' , '03' , 20);
insert into score values('05' , '01' , 76);
insert into score values('05' , '02' , 87);
insert into score values('06' , '01' , 31);
insert into score values('06' , '03' , 34);
insert into score values('07' , '02' , 89);
insert into score values('07' , '03' , 98);
insert into score values('08' , '02' , 89);
insert into score values('09' , '02' , 89);

   
    

View the data ：

3. Ranking without grouping

3.1 Continuous ranking

1. Use ROW_NUMBER Realization ：

SELECT score,
ROW_NUMBER() OVER (ORDER BY score DESC) ranking
FROM score;

   
    

2. Use Variable Realization ：

SELECT s.score, (@cur_rank := @cur_rank + 1) ranking
FROM score s, (SELECT @cur_rank := 0) r
ORDER BY score DESC;

   
    

The result is shown in Fig. ：

3.2 Juxtaposed jump rankings

1. Use RANK Realization ：

SELECT course_id, score,
RANK() OVER(ORDER BY score DESC)
FROM score;

   
    

2. Use Variable and IF Statements for ：

SELECT s.score,
@rank_counter := @rank_counter + 1,
IF(@pre_score = s.score, @cur_rank, @cur_rank := @rank_counter) ranking,
@pre_score := s.score
FROM score s, (SELECT @cur_rank :=0, @pre_score := NULL, @rank_counter := 0) r
ORDER BY s.score DESC;

   
    

3. Use Variable and CASE Statements for ：

SELECT s.score,
@rank_counter := @rank_counter + 1,
(
  CASE
  WHEN @pre_score = s.score THEN @cur_rank
  WHEN @pre_score := s.score THEN @cur_rank := @rank_counter
  END
) ranking
FROM score s, (SELECT @cur_rank :=0, @pre_score := NULL, @rank_counter := 0) r
ORDER BY s.score DESC;

   
    

The result is shown in Fig. ：

3.3 Juxtaposed in a row

1. Use DENSE_RANK Realization ：

SELECT course_id, score,
DENSE_RANK() OVER(ORDER BY score DESC) FROM score;

   
    

2. Use Variable and IF Statements for ：

SELECT s.score,
IF(@pre_score = s.score, @cur_rank, @cur_rank := @cur_rank + 1) ranking,
@pre_score := s.score
FROM score s, (SELECT @cur_rank :=0, @pre_score = NULL) r
ORDER BY s.score DESC;

   
    

3. Use Variable and CASE Statements for ：

SELECT s.score,
(
  CASE
  WHEN @pre_score = s.score THEN @cur_rank
  WHEN @pre_score := s.score THEN @cur_rank := @cur_rank + 1
  END
) ranking
FROM score s, (SELECT @cur_rank :=0, @pre_score = NULL) r
ORDER BY s.score DESC;

   
    

The result is shown in Fig. ：

4. Group ranking

4.1 Rank consecutively in groups

1. Use ROW_NUMBER Realization ：

SELECT course_id, score,
ROW_NUMBER() OVER (PARTITION BY course_id ORDER BY score DESC) ranking FROM score;

   
    

2. Use Variable and IF Statements for ：

SELECT s.course_id, s.score,
IF(@pre_course_id = s.course_id, @cur_rank := @cur_rank + 1, @cur_rank := 1) ranking,
@pre_course_id := s.course_id
FROM score s, (SELECT @cur_rank := 0, @pre_course_id := NULL) r
ORDER BY course_id, score DESC;

   
    

The result is shown in Fig. ：

4.2 Group side by side jump ranking

1. Use RANK Realization ：

SELECT course_id, score,
RANK() OVER(PARTITION BY course_id ORDER BY score DESC)
FROM score;

   
    

2. Use Variable and IF Statements for ：

SELECT s.course_id, s.score,
IF(@pre_course_id = s.course_id,
   @rank_counter := @rank_counter + 1,
   @rank_counter := 1) temp1,
IF(@pre_course_id = s.course_id,
   IF(@pre_score = s.score, @cur_rank, @cur_rank := @rank_counter),
   @cur_rank := 1) ranking,
@pre_score := s.score temp2,
@pre_course_id := s.course_id temp3
FROM score s, (SELECT @cur_rank := 0, @pre_course_id := NULL, @pre_score := NULL, @rank_counter := 1)r
ORDER BY s.course_id, s.score DESC;

   
    

The result is shown in Fig. ：

4.3 Group parallel continuous ranking

1. Use DENSE_RANK Realization ：

SELECT course_id, score,
DENSE_RANK() OVER(PARTITION BY course_id ORDER BY score DESC)
FROM score;

   
    

2. Use Variable and IF Statements for ：

SELECT s.course_id, s.score,
IF(@pre_course_id = s.course_id,
   IF(@pre_score = s.score, @cur_rank, @cur_rank := @cur_rank + 1),
   @cur_rank := 1) ranking,
@pre_score := s.score,
@pre_course_id := s.course_id
FROM score s, (SELECT @cur_rank :=0, @pre_score = NULL, @pre_course_id := NULL) r
ORDER BY course_id, score DESC;

   
    

The above IF Conditions are extracted ：

SELECT s.course_id, s.score,
IF(@pre_score = s.score, @cur_rank, @cur_rank := @cur_rank + 1) temp1,
@pre_score := s.score temp2,
IF(@pre_course_id = s.course_id, @cur_rank, @cur_rank := 1) ranking,
@pre_course_id := s.course_id
FROM score s, (SELECT @cur_rank :=0, @pre_score = NULL, @pre_course_id := NULL) r
ORDER BY course_id, score DESC;

   
    

The result is shown in Fig. ：