Clickhouse的 MySQL ELT和interval 功能等同实现

在MySQL和Clickhouse中分别创建表：

mysql> create table scores(id int not null auto_increment primary key,user_id bigint,scores decimal(10,2));

Clickhouse> create table scores(user_id bigint,scores decimal(10,2)) engine=Memory;


insert into scores(user_id,scores)values(101,60.5),(102,50.25),(103,80),(104,90),(105,99),(106,92.75)
,(107,75),(108,89.75),(109,90.25),(110,0),(111,60),(112,100);



mysql> select user_id,scores,interval(scores,0,60,80,90) p from scores;
+---------+--------+---+
| user_id | scores | p |
+---------+--------+---+
|     101 |  60.50 | 2 |
|     102 |  50.25 | 1 |
|     103 |  80.00 | 3 |
|     104 |  90.00 | 4 |
|     105 |  99.00 | 4 |
|     106 |  92.75 | 4 |
|     107 |  75.00 | 2 |
|     108 |  89.75 | 3 |
|     109 |  90.25 | 4 |
|     110 |   0.00 | 1 |
|     111 |  60.00 | 2 |
|     112 | 100.00 | 4 |
+---------+--------+---+
12 rows in set (0.00 sec)

适用于多数RDBMS数据库： 

select case when scores>=0 and scores <60 then '[0,60)' 
             when scores>=60 and scores <80 then '[60,80)'  
			 when scores>=80 and scores <90 then '[80,90)' 
			 when scores>=90 and scores <=100 then '[90,100]' 
			 end p
			 ,count(user_id) 
from scores group by p order by 1;

+----------+----------------+
| p        | count(user_id) |
+----------+----------------+
| [0,60)   |              2 |
| [60,80)  |              3 |
| [80,90)  |              2 |
| [90,100] |              5 |
+----------+----------------+
4 rows in set (0.00 sec)

MySQL中的ELT和Interval 配合使用：

mysql> set sql_mode='STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION';
Query OK, 0 rows affected (0.00 sec)


mysql> select elt(interval(scores,0,60,80,90),'[0,60)','[60-80)','[80,90)','[90,100]') p,count(user_id) 
from scores 
group by elt(interval(scores,0,60,80,90),'[0,60)','[60-80)','[80,90)','[90,100]') order by 1 ;
+----------+----------------+
| p        | count(user_id) |
+----------+----------------+
| [0,60)   |              2 |
| [60-80)  |              3 |
| [80,90)  |              2 |
| [90,100] |              5 |
+----------+----------------+
4 rows in set (0.00 sec)


MySQL中 也支持列的别名
mysql> select elt(interval(scores,0,60,80,90),'[0,60)','[60-80)','[80,90)','[90,100]') p,count(user_id) 
 from scores  group by p order by 1; 

Clickhouse的multiif函数：
 

Clickhouse> select case when scores>=0 and scores <60 then '[0,60)' when scores>=60 and scores <80 then '[60,80)'  when scores>=80 and scores <90 then '[80,90)' when scores>=90 and scores <=100 then '[90,100]' end p,count(user_id) from scores group by p order by 1;

SELECT 
    multiIf((scores >= 0) AND (scores < 60), '[0,60)', (scores >= 60) AND (scores < 80), '[60,80)', (scores >= 80) AND (scores < 90), '[80,90)', (scores >= 90) AND (scores <= 100), '[90,100]', NULL) AS p,
    count(user_id)
FROM scores
GROUP BY p
ORDER BY 1 ASC

┌─p────────┬─count(user_id)─┐
│ [0,60)   │              2 │
│ [60,80)  │              3 │
│ [90,100] │              5 │
│ [80,90)  │              2 │
└──────────┴────────────────┘

4 rows in set. Elapsed: 0.005 sec.