clickhouse实现 lag/lead

 clickhouse中的lead和lag实现有多种方法，在标准的SQL中使用的windows function即可实现。

示例数据：
CREATE TABLE llexample (
    g Int32,
    a Date )
ENGINE = Memory;
 
INSERT INTO llexample SELECT
    number % 3,
    toDate('2020-01-01') + number
FROM numbers(10);
 
SELECT * FROM llexample ORDER BY g,a;
 
┌─g─┬──────────a─┐
│ 0 │ 2020-01-01 │
│ 0 │ 2020-01-04 │
│ 0 │ 2020-01-07 │
│ 0 │ 2020-01-10 │
│ 1 │ 2020-01-02 │
│ 1 │ 2020-01-05 │
│ 1 │ 2020-01-08 │
│ 2 │ 2020-01-03 │
│ 2 │ 2020-01-06 │
│ 2 │ 2020-01-09 │
└───┴────────────┘
 
方法1：array
select g, (arrayJoin(tuple_ll) as ll).1 a, ll.2 prev, ll.3 next
from (
select g, arrayMap( i,j,k -> (i,j,k), 
                    arraySort(groupArray(a)) as aa, 
                    arrayPopBack(arrayPushFront(aa, toDate(0))),
                    arrayPopFront(arrayPushBack(aa, toDate(0))) ) tuple_ll
from llexample
group by g)
order by g, a;
 
┌─g─┬──────────a─┬───────prev─┬───────next─┐
│ 0 │ 2020-01-01 │ 1970-01-01 │ 2020-01-04 │
│ 0 │ 2020-01-04 │ 2020-01-01 │ 2020-01-07 │
│ 0 │ 2020-01-07 │ 2020-01-04 │ 2020-01-10 │
│ 0 │ 2020-01-10 │ 2020-01-07 │ 1970-01-01 │
│ 1 │ 2020-01-02 │ 1970-01-01 │ 2020-01-05 │
│ 1 │ 2020-01-05 │ 2020-01-02 │ 2020-01-08 │
│ 1 │ 2020-01-08 │ 2020-01-05 │ 1970-01-01 │
│ 2 │ 2020-01-03 │ 1970-01-01 │ 2020-01-06 │
│ 2 │ 2020-01-06 │ 2020-01-03 │ 2020-01-09 │
│ 2 │ 2020-01-09 │ 2020-01-06 │ 1970-01-01 │
└───┴────────────┴────────────┴────────────┘
 
方法2：Using window functions (starting from Clickhouse 21.3)
SET allow_experimental_window_functions = 1;
 
SELECT
    g,
    a,
    any(a) OVER (PARTITION BY g ORDER BY a ASC ROWS 
                 BETWEEN 1 PRECEDING AND 1 PRECEDING) AS prev,
    any(a) OVER (PARTITION BY g ORDER BY a ASC ROWS 
                 BETWEEN 1 FOLLOWING AND 1 FOLLOWING) AS next
FROM llexample
ORDER BY
    g ASC,
    a ASC;
 
┌─g─┬──────────a─┬───────prev─┬───────next─┐
│ 0 │ 2020-01-01 │ 1970-01-01 │ 2020-01-04 │
│ 0 │ 2020-01-04 │ 2020-01-01 │ 2020-01-07 │
│ 0 │ 2020-01-07 │ 2020-01-04 │ 2020-01-10 │
│ 0 │ 2020-01-10 │ 2020-01-07 │ 1970-01-01 │
│ 1 │ 2020-01-02 │ 1970-01-01 │ 2020-01-05 │
│ 1 │ 2020-01-05 │ 2020-01-02 │ 2020-01-08 │
│ 1 │ 2020-01-08 │ 2020-01-05 │ 1970-01-01 │
│ 2 │ 2020-01-03 │ 1970-01-01 │ 2020-01-06 │
│ 2 │ 2020-01-06 │ 2020-01-03 │ 2020-01-09 │
│ 2 │ 2020-01-09 │ 2020-01-06 │ 1970-01-01 │
└───┴────────────┴────────────┴────────────┘
 
方法3：Using lagInFrame/leadInFrame (starting from ClickHouse 21.4)
 
SELECT
    g,
    a,
    lagInFrame(a) OVER (PARTITION BY g ORDER BY a ASC ROWS 
                 BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) AS prev,
    leadInFrame(a) OVER (PARTITION BY g ORDER BY a ASC ROWS 
                 BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) AS next
FROM llexample
ORDER BY
    g ASC,
    a ASC;
 
┌─g─┬──────────a─┬───────prev─┬───────next─┐
│ 0 │ 2020-01-01 │ 1970-01-01 │ 2020-01-04 │
│ 0 │ 2020-01-04 │ 2020-01-01 │ 2020-01-07 │
│ 0 │ 2020-01-07 │ 2020-01-04 │ 2020-01-10 │
│ 0 │ 2020-01-10 │ 2020-01-07 │ 1970-01-01 │
│ 1 │ 2020-01-02 │ 1970-01-01 │ 2020-01-05 │
│ 1 │ 2020-01-05 │ 2020-01-02 │ 2020-01-08 │
│ 1 │ 2020-01-08 │ 2020-01-05 │ 1970-01-01 │
│ 2 │ 2020-01-03 │ 1970-01-01 │ 2020-01-06 │
│ 2 │ 2020-01-06 │ 2020-01-03 │ 2020-01-09 │
│ 2 │ 2020-01-09 │ 2020-01-06 │ 1970-01-01 │
└───┴────────────┴────────────┴────────────┘
 
方法4：Using neighbor (no grouping, incorrect result over blocks)
SELECT
    g,
    a,
    neighbor(a, -1) AS prev,
    neighbor(a, 1) AS next
FROM
(
    SELECT *
    FROM llexample
    ORDER BY
        g ASC,
        a ASC
);
 
┌─g─┬──────────a─┬───────prev─┬───────next─┐
│ 0 │ 2020-01-01 │ 1970-01-01 │ 2020-01-04 │
│ 0 │ 2020-01-04 │ 2020-01-01 │ 2020-01-07 │
│ 0 │ 2020-01-07 │ 2020-01-04 │ 2020-01-10 │
│ 0 │ 2020-01-10 │ 2020-01-07 │ 2020-01-02 │
│ 1 │ 2020-01-02 │ 2020-01-10 │ 2020-01-05 │
│ 1 │ 2020-01-05 │ 2020-01-02 │ 2020-01-08 │
│ 1 │ 2020-01-08 │ 2020-01-05 │ 2020-01-03 │
│ 2 │ 2020-01-03 │ 2020-01-08 │ 2020-01-06 │
│ 2 │ 2020-01-06 │ 2020-01-03 │ 2020-01-09 │
│ 2 │ 2020-01-09 │ 2020-01-06 │ 1970-01-01 │
└───┴────────────┴────────────┴────────────┘
 

　　

参考：clickhouse lag/lead

https://kb.altinity.com/altinity-kb-queries-and-syntax/lag-lead/