?clickhouse中的lead和lag實現有多種方法，在標準的SQL中使用的windows function即可實現。

示例數據： CREATE TABLE llexample (g Int32,a Date ) ENGINE = Memory;INSERT INTO llexample SELECTnumber % 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;SELECTg,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 BYg 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)SELECTg,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 BYg 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) SELECTg,a,neighbor(a, -1) AS prev,neighbor(a, 1) AS next FROM (SELECT *FROM llexampleORDER BYg 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 │ └───┴────────────┴────────────┴────────────┘

參考：

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

總結

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