running_difference

running_difference

description

Syntax

T running_difference(T x) 计算数据块中连续行值的差值。该函数的结果取决于受影响的数据块和块中数据的顺序。

计算 running_difference 期间使用的行顺序可能与返回给用户的行顺序不同。所以结果是不稳定的。此函数会在后续版本中废弃。 推荐使用窗口函数完成预期功能。举例如下：

-- running difference(x)
SELECT running_difference(x) FROM t ORDER BY k;

-- 窗口函数
SELECT x - lag(x, 1, 0) OVER (ORDER BY k) FROM t;

Arguments

x - 一列数据.数据类型可以是TINYINT,SMALLINT,INT,BIGINT,LARGEINT,FLOAT,DOUBLE,DATE,DATETIME,DECIMAL

Returned value

第一行返回 0，随后的每一行返回与前一行的差值。

example

DROP TABLE IF EXISTS running_difference_test;

CREATE TABLE running_difference_test (
    `id` int NOT NULL COMMENT 'id',
    `day` date COMMENT 'day', 
    `time_val` datetime COMMENT 'time_val',
    `doublenum` double NULL COMMENT 'doublenum'
)
DUPLICATE KEY(id) 
DISTRIBUTED BY HASH(id) BUCKETS 3 
PROPERTIES ( 
    "replication_num" = "1"
); 
                                                  
INSERT into running_difference_test (id, day, time_val,doublenum) values ('1', '2022-10-28', '2022-03-12 10:41:00', null),
                                                   ('2','2022-10-27', '2022-03-12 10:41:02', 2.6),
                                                   ('3','2022-10-28', '2022-03-12 10:41:03', 2.5),
                                                   ('4','2022-9-29', '2022-03-12 10:41:03', null),
                                                   ('5','2022-10-31', '2022-03-12 10:42:01', 3.3),
                                                   ('6', '2022-11-08', '2022-03-12 11:05:04', 4.7); 

SELECT * from running_difference_test ORDER BY id ASC;

+------+------------+---------------------+-----------+
| id   | day        | time_val            | doublenum |
+------+------------+---------------------+-----------+
|    1 | 2022-10-28 | 2022-03-12 10:41:00 |      NULL |
|    2 | 2022-10-27 | 2022-03-12 10:41:02 |       2.6 |
|    3 | 2022-10-28 | 2022-03-12 10:41:03 |       2.5 |
|    4 | 2022-09-29 | 2022-03-12 10:41:03 |      NULL |
|    5 | 2022-10-31 | 2022-03-12 10:42:01 |       3.3 |
|    6 | 2022-11-08 | 2022-03-12 11:05:04 |       4.7 |
+------+------------+---------------------+-----------+

SELECT
    id,
    running_difference(id) AS delta
FROM
(
    SELECT
        id,
        day,
        time_val,
        doublenum
    FROM running_difference_test
)as runningDifference ORDER BY id ASC;

+------+-------+
| id   | delta |
+------+-------+
|    1 |     0 |
|    2 |     1 |
|    3 |     1 |
|    4 |     1 |
|    5 |     1 |
|    6 |     1 |
+------+-------+

SELECT
    day,
    running_difference(day) AS delta
FROM
(
    SELECT
        id,
        day,
        time_val,
        doublenum
    FROM running_difference_test
)as runningDifference ORDER BY id ASC;

+------------+-------+
| day        | delta |
+------------+-------+
| 2022-10-28 |     0 |
| 2022-10-27 |    -1 |
| 2022-10-28 |     1 |
| 2022-09-29 |   -29 |
| 2022-10-31 |    32 |
| 2022-11-08 |     8 |
+------------+-------+

SELECT
    time_val,
    running_difference(time_val) AS delta
FROM
(
    SELECT
        id,
        day,
        time_val,
        doublenum
    FROM running_difference_test
)as runningDifference ORDER BY id ASC;

+---------------------+-------+
| time_val            | delta |
+---------------------+-------+
| 2022-03-12 10:41:00 |     0 |
| 2022-03-12 10:41:02 |     2 |
| 2022-03-12 10:41:03 |     1 |
| 2022-03-12 10:41:03 |     0 |
| 2022-03-12 10:42:01 |    58 |
| 2022-03-12 11:05:04 |  1383 |
+---------------------+-------+

SELECT
    doublenum,
    running_difference(doublenum) AS delta
FROM
(
    SELECT
        id,
        day,
        time_val,
        doublenum
    FROM running_difference_test
)as runningDifference ORDER BY id ASC;

+-----------+----------------------+
| doublenum | delta                |
+-----------+----------------------+
|      NULL |                 NULL |
|       2.6 |                 NULL |
|       2.5 | -0.10000000000000009 |
|      NULL |                 NULL |
|       3.3 |                 NULL |
|       4.7 |   1.4000000000000004 |
+-----------+----------------------+

keywords

running_difference