如何在 PostgreSQL 中移动整个组？
How to shift whole groups in PostgreSQL?
我有一个 table 结构如下（对于相当长的数据示例表示歉意，但无法用较小的行数重现该问题）：
CREATE TABLE example_tbl (
id CHAR(1),
pid INT,
sid INT,
tid VARCHAR(10),
other_columns INT
)
INSERT INTO example_tbl (id, pid, sid, tid, other_columns)
VALUES
('c', 157, 85, 'A32', 1),
('c', 157, 85, 'A32', 2),
('c', 157, 85, 'A32', 3),
('c', 157, 85, 'A32', 4),
('c', 157, 85, 'A32', 5),
('c', 157, 85, 'A32', 6),
('c', 157, 85, 'A32', 7),
('c', 157, 85, 'A32', 8),
('c', 157, 85, 'A32', 9),
('c', 157, 85, 'A32', 10),
('c', 157, 85, 'A32', 11),
('Q', 157, 81, 'A62', 1),
('Q', 157, 81, 'A62', 2),
('Q', 157, 81, 'A62', 3),
('Q', 157, 81, 'A62', 4),
('Q', 157, 81, 'A62', 5),
('Q', 157, 81, 'A62', 6),
('Q', 157, 81, 'A62', 7),
('Q', 157, 81, 'A62', 8),
('Q', 157, 81, 'A62', 9),
('Q', 157, 81, 'A62', 10),
('Q', 157, 81, 'A62', 11),
('f', 598, 51, 'A62', NULL),
('w', 598, 49, 'A32', 9),
('Z', 598, 44, 'A62', NULL),
('r', 598, 16, 'A32', 10),
('O', 118, 93, 'A32', 1),
('G', 118, 38, 'A32', 4),
('U', 118, 90, 'A32', 1),
('U', 118, 90, 'A32', 2),
('U', 118, 90, 'A32', 3),
('U', 118, 90, 'A32', 4),
('U', 118, 90, 'A32', 5),
('U', 118, 90, 'A32', 6),
('U', 118, 90, 'A32', 7),
('U', 118, 90, 'A32', 8),
('U', 118, 90, 'A32', 9),
('U', 118, 90, 'A32', 10),
('U', 118, 90, 'A32', 11),
('m', 118, 37, 'A62', 1),
('J', 118, 54, 'A32', 20),
('a', 118, 59, 'A32', 11),
('s', 118, 18, 'A62', 8),
('y', 118, 33, 'A62', NULL),
('N', 118, 79, 'A62', NULL),
('l', 118, 35, 'A32', 9),
('n', 118, 63, 'A32', 5),
('R', 118, 86, 'A62', 1),
('R', 118, 86, 'A62', 2),
('R', 118, 86, 'A62', 3),
('R', 118, 86, 'A62', 4),
('R', 118, 86, 'A62', 5),
('R', 118, 86, 'A62', 6),
('R', 118, 86, 'A62', 7),
('R', 118, 86, 'A62', 8),
('R', 118, 86, 'A62', 9),
('R', 118, 86, 'A62', 10),
('R', 118, 86, 'A62', 11),
('H', 118, 23, 'A32', 1),
('H', 118, 23, 'A32', 2),
('H', 118, 23, 'A32', 3),
('H', 118, 23, 'A32', 4),
('H', 118, 23, 'A32', 5),
('H', 118, 23, 'A32', 6),
('H', 118, 23, 'A32', 7),
('H', 118, 23, 'A32', 8),
('H', 118, 23, 'A32', 9),
('H', 118, 23, 'A32', 10),
('H', 118, 23, 'A32', 11),
('B', 118, 43, 'A62', 39),
('h', 118, 60, 'A62', NULL),
('p', 118, 72, 'A32', 1),
('v', 118, 22, 'A32', 5),
('I', 118, 89, 'A62', 9),
('T', 118, 17, 'A62', 1),
('F', 118, 41, 'A32', 10),
('z', 118, 55, 'A32', 6),
('Y', 118, 75, 'A32', NULL),
('u', 118, 48, 'A62', 9),
('x', 783, 27, 'A32', 10),
('V', 783, 11, 'A62', 8),
('i', 783, 61, 'A62', 1),
('i', 783, 61, 'A62', 2),
('i', 783, 61, 'A62', 3),
('i', 783, 61, 'A62', 4),
('i', 783, 61, 'A62', 5),
('i', 783, 61, 'A62', 6),
('i', 783, 61, 'A62', 7),
('i', 783, 61, 'A62', 8),
('i', 783, 61, 'A62', 9),
('i', 783, 61, 'A62', 10),
('i', 783, 61, 'A62', 11);
id 列定义了事件。我想在 tid 定义的组中添加一个包含上一个事件的 id 的列。数据应根据 pid（自定义顺序，其中 157 < 598 < 118 < 783）和 sid 排序。棘手的部分是有些事件有 11 行，有些只有 1 行。
other_columns 代表所有其他应该保留的列。
我尝试使用 LAG() window 具有预先计算的偏移量的函数，如下所示：
WITH example_tbl_with_offset AS (
SELECT * FROM example_tbl
LEFT JOIN (SELECT id, COUNT(id)::int AS lag_offset
FROM example_tbl
GROUP BY id) AS offset_tbl
USING (id)
)
SELECT
*,
LAG(id, lag_offset) OVER (PARTITION BY tid
ORDER BY (CASE
WHEN pid = 157 THEN 1
WHEN pid = 598 THEN 2
WHEN pid = 118 THEN 3
WHEN pid = 783 THEN 4
END, sid
)) AS prev_id
FROM example_tbl_with_offset;
然而，尽管 prev_id 列似乎对前几个事件有效，但它最终失去了踪迹。
预期输出附在下面：
CREATE TABLE expected_output (
id CHAR(1),
pid INT,
sid INT,
tid VARCHAR(10),
prev_id CHAR(1)
)
INSERT INTO expected_output (id, pid, sid, tid, prev_id)
VALUES
('Q', 157, 81, 'A62', NULL),
('Q', 157, 81, 'A62', NULL),
('Q', 157, 81, 'A62', NULL),
('Q', 157, 81, 'A62', NULL),
('Q', 157, 81, 'A62', NULL),
('Q', 157, 81, 'A62', NULL),
('Q', 157, 81, 'A62', NULL),
('Q', 157, 81, 'A62', NULL),
('Q', 157, 81, 'A62', NULL),
('Q', 157, 81, 'A62', NULL),
('Q', 157, 81, 'A62', NULL),
('c', 157, 85, 'A32', NULL),
('c', 157, 85, 'A32', NULL),
('c', 157, 85, 'A32', NULL),
('c', 157, 85, 'A32', NULL),
('c', 157, 85, 'A32', NULL),
('c', 157, 85, 'A32', NULL),
('c', 157, 85, 'A32', NULL),
('c', 157, 85, 'A32', NULL),
('c', 157, 85, 'A32', NULL),
('c', 157, 85, 'A32', NULL),
('c', 157, 85, 'A32', NULL),
('r', 598, 16, 'A32', 'c'),
('Z', 598, 44, 'A62', 'Q'),
('w', 598, 49, 'A32', 'r'),
('f', 598, 51, 'A62', 'Z'),
('T', 118, 17, 'A62', 'f'),
('s', 118, 18, 'A62', 'T'),
('v', 118, 22, 'A32', 'w'),
('H', 118, 23, 'A32', 'v'),
('H', 118, 23, 'A32', 'v'),
('H', 118, 23, 'A32', 'v'),
('H', 118, 23, 'A32', 'v'),
('H', 118, 23, 'A32', 'v'),
('H', 118, 23, 'A32', 'v'),
('H', 118, 23, 'A32', 'v'),
('H', 118, 23, 'A32', 'v'),
('H', 118, 23, 'A32', 'v'),
('H', 118, 23, 'A32', 'v'),
('H', 118, 23, 'A32', 'v'),
('y', 118, 33, 'A62', 's'),
('l', 118, 35, 'A32', 'H'),
('m', 118, 37, 'A62', 'y'),
('G', 118, 38, 'A32', 'I'),
('F', 118, 41, 'A32', 'G'),
('B', 118, 43, 'A62', 'm'),
('u', 118, 48, 'A62', 'B'),
('J', 118, 54, 'A32', 'F'),
('z', 118, 55, 'A32', 'J'),
('a', 118, 59, 'A32', 'z'),
('h', 118, 60, 'A62', 'u'),
('n', 118, 63, 'A32', 'a'),
('p', 118, 72, 'A32', 'n'),
('Y', 118, 75, 'A32', 'p'),
('N', 118, 79, 'A62', 'h'),
('R', 118, 86, 'A62', 'N'),
('R', 118, 86, 'A62', 'N'),
('R', 118, 86, 'A62', 'N'),
('R', 118, 86, 'A62', 'N'),
('R', 118, 86, 'A62', 'N'),
('R', 118, 86, 'A62', 'N'),
('R', 118, 86, 'A62', 'N'),
('R', 118, 86, 'A62', 'N'),
('R', 118, 86, 'A62', 'N'),
('R', 118, 86, 'A62', 'N'),
('R', 118, 86, 'A62', 'N'),
('I', 118, 89, 'A62', 'R'),
('U', 118, 90, 'A32', 'Y'),
('U', 118, 90, 'A32', 'Y'),
('U', 118, 90, 'A32', 'Y'),
('U', 118, 90, 'A32', 'Y'),
('U', 118, 90, 'A32', 'Y'),
('U', 118, 90, 'A32', 'Y'),
('U', 118, 90, 'A32', 'Y'),
('U', 118, 90, 'A32', 'Y'),
('U', 118, 90, 'A32', 'Y'),
('U', 118, 90, 'A32', 'Y'),
('U', 118, 90, 'A32', 'Y'),
('O', 118, 93, 'A32', 'U'),
('V', 783, 11, 'A62', 'I'),
('x', 783, 27, 'A32', 'O'),
('i', 783, 61, 'A62', 'V'),
('i', 783, 61, 'A62', 'V'),
('i', 783, 61, 'A62', 'V'),
('i', 783, 61, 'A62', 'V'),
('i', 783, 61, 'A62', 'V'),
('i', 783, 61, 'A62', 'V'),
('i', 783, 61, 'A62', 'V'),
('i', 783, 61, 'A62', 'V'),
('i', 783, 61, 'A62', 'V'),
('i', 783, 61, 'A62', 'V'),
('i', 783, 61, 'A62', 'V');
以下顺序可能更容易理解实际逻辑：
SELECT * FROM expected_output
ORDER BY tid, CASE
WHEN pid = 157 THEN 1
WHEN pid = 598 THEN 2
WHEN pid = 118 THEN 3
WHEN pid = 783 THEN 4
END, sid;
@编辑：我的PostgreSQL版本是9.5.
这是有效的，希望有人能找到更好的解决方案
select m.* from (
select *, lag(id,1) over ( PARTITION BY tid
order by (CASE
WHEN pid = 157 THEN 1
WHEN pid = 598 THEN 2
WHEN pid = 118 THEN 3
WHEN pid = 783 THEN 4
END, sid
)
) from ( select distinct * from example_tbl et )a )
m,
example_tbl n
where m.id = n.id and m.pid = n.pid and m.sid = n.sid and m.tid = n.tid
order by (CASE
WHEN m.pid = 157 THEN 1
WHEN m.pid = 598 THEN 2
WHEN m.pid = 118 THEN 3
WHEN m.pid = 783 THEN 4
END, m.sid
)
类似的解决方案：
with
a as (
select distinct *,
case
WHEN pid = 157 THEN 1
WHEN pid = 598 THEN 2
WHEN pid = 118 THEN 3
WHEN pid = 783 THEN 4
end as cat
from example_tbl
),
b as (
select id, cat,
lag(id, 1) over(partition by tid order by cat, sid) prev_id
from a
)
select c.*, b.prev_id
from example_tbl c
left join b using (id)
order by b.cat,c.sid
Postgres 11 的主要新特性之一在 release notes:
中是这样宣传的
- Window functions now support all framing options shown in the SQL:2011 standard, including
RANGE distance PRECEDING/FOLLOWING, GROUPS mode, and frame exclusion options
使用这个，有一个解决方案 single window function in a 单身SELECT:
SELECT *, first_value(id) OVER (PARTITION BY tid
ORDER BY CASE pid
WHEN 157 THEN 1
WHEN 598 THEN 2
WHEN 118 THEN 3
WHEN 783 THEN 4
END, sid
GROUPS BETWEEN 1 PRECEDING AND 1 PRECEDING
) AS prev_id
FROM example_tbl;
db<>fiddle here
应该也表现不错。
也适用于您的扩展测试设置，但不适用于版本 11 之前的 Postgres。
In GROUPS mode, the offset again must yield a non-null, non-negative
integer, and the option means that the frame starts or ends the
specified number of peer groups before or after the current row's peer
group, where a peer group is a set of rows that are equivalent in the
ORDER BY ordering.
所选的框架定义GROUPS BETWEEN 1 PRECEDING AND 1 PRECEDING完全符合您的需要。
您的描述和测试数据似乎暗示 sid 和 id 的变化是一致的。所以 window 框架只包含一个 id 值。 min() 或 max() 也可以，但我选择 first_value() 是最便宜的。而且因为它适用于任何数据类型，即使 min() 或 max() 会失败（如 json）。
此外，使用更短（并且稍微便宜）的“简单”或“转换”CASE。参见：
- Display column name with max value between several columns
对于 Postgres 9.5
这适用于您过时的 Postgres 9.5 版：
SELECT e.*, p.prev_id
FROM example_tbl e
JOIN (
SELECT *
, lag(id) OVER (PARTITION BY tid
ORDER BY CASE pid
WHEN 157 THEN 1
WHEN 598 THEN 2
WHEN 118 THEN 3
WHEN 783 THEN 4
END, sid) AS prev_id
FROM (
SELECT DISTINCT ON (tid, pid, sid)
tid, pid, sid, id
FROM example_tbl
) dist
) p USING (tid, pid, sid);
db<>fiddle here
这是假设 tid、pid、sid 被定义为 NOT NULL。否则，你需要做更多。
使用 (tid, pid, sid) 的不同组合得出 table。同样，id 只是一个负载列。关于 DISTINCT ON:
- Select first row in each GROUP BY group?
现在，具有默认 window 框架的 lag() 完成了从“前一”行获取 id 的工作。
加入完整table。
我有一个 table 结构如下（对于相当长的数据示例表示歉意，但无法用较小的行数重现该问题）：
CREATE TABLE example_tbl (
id CHAR(1),
pid INT,
sid INT,
tid VARCHAR(10),
other_columns INT
)
INSERT INTO example_tbl (id, pid, sid, tid, other_columns)
VALUES
('c', 157, 85, 'A32', 1),
('c', 157, 85, 'A32', 2),
('c', 157, 85, 'A32', 3),
('c', 157, 85, 'A32', 4),
('c', 157, 85, 'A32', 5),
('c', 157, 85, 'A32', 6),
('c', 157, 85, 'A32', 7),
('c', 157, 85, 'A32', 8),
('c', 157, 85, 'A32', 9),
('c', 157, 85, 'A32', 10),
('c', 157, 85, 'A32', 11),
('Q', 157, 81, 'A62', 1),
('Q', 157, 81, 'A62', 2),
('Q', 157, 81, 'A62', 3),
('Q', 157, 81, 'A62', 4),
('Q', 157, 81, 'A62', 5),
('Q', 157, 81, 'A62', 6),
('Q', 157, 81, 'A62', 7),
('Q', 157, 81, 'A62', 8),
('Q', 157, 81, 'A62', 9),
('Q', 157, 81, 'A62', 10),
('Q', 157, 81, 'A62', 11),
('f', 598, 51, 'A62', NULL),
('w', 598, 49, 'A32', 9),
('Z', 598, 44, 'A62', NULL),
('r', 598, 16, 'A32', 10),
('O', 118, 93, 'A32', 1),
('G', 118, 38, 'A32', 4),
('U', 118, 90, 'A32', 1),
('U', 118, 90, 'A32', 2),
('U', 118, 90, 'A32', 3),
('U', 118, 90, 'A32', 4),
('U', 118, 90, 'A32', 5),
('U', 118, 90, 'A32', 6),
('U', 118, 90, 'A32', 7),
('U', 118, 90, 'A32', 8),
('U', 118, 90, 'A32', 9),
('U', 118, 90, 'A32', 10),
('U', 118, 90, 'A32', 11),
('m', 118, 37, 'A62', 1),
('J', 118, 54, 'A32', 20),
('a', 118, 59, 'A32', 11),
('s', 118, 18, 'A62', 8),
('y', 118, 33, 'A62', NULL),
('N', 118, 79, 'A62', NULL),
('l', 118, 35, 'A32', 9),
('n', 118, 63, 'A32', 5),
('R', 118, 86, 'A62', 1),
('R', 118, 86, 'A62', 2),
('R', 118, 86, 'A62', 3),
('R', 118, 86, 'A62', 4),
('R', 118, 86, 'A62', 5),
('R', 118, 86, 'A62', 6),
('R', 118, 86, 'A62', 7),
('R', 118, 86, 'A62', 8),
('R', 118, 86, 'A62', 9),
('R', 118, 86, 'A62', 10),
('R', 118, 86, 'A62', 11),
('H', 118, 23, 'A32', 1),
('H', 118, 23, 'A32', 2),
('H', 118, 23, 'A32', 3),
('H', 118, 23, 'A32', 4),
('H', 118, 23, 'A32', 5),
('H', 118, 23, 'A32', 6),
('H', 118, 23, 'A32', 7),
('H', 118, 23, 'A32', 8),
('H', 118, 23, 'A32', 9),
('H', 118, 23, 'A32', 10),
('H', 118, 23, 'A32', 11),
('B', 118, 43, 'A62', 39),
('h', 118, 60, 'A62', NULL),
('p', 118, 72, 'A32', 1),
('v', 118, 22, 'A32', 5),
('I', 118, 89, 'A62', 9),
('T', 118, 17, 'A62', 1),
('F', 118, 41, 'A32', 10),
('z', 118, 55, 'A32', 6),
('Y', 118, 75, 'A32', NULL),
('u', 118, 48, 'A62', 9),
('x', 783, 27, 'A32', 10),
('V', 783, 11, 'A62', 8),
('i', 783, 61, 'A62', 1),
('i', 783, 61, 'A62', 2),
('i', 783, 61, 'A62', 3),
('i', 783, 61, 'A62', 4),
('i', 783, 61, 'A62', 5),
('i', 783, 61, 'A62', 6),
('i', 783, 61, 'A62', 7),
('i', 783, 61, 'A62', 8),
('i', 783, 61, 'A62', 9),
('i', 783, 61, 'A62', 10),
('i', 783, 61, 'A62', 11);
id 列定义了事件。我想在 tid 定义的组中添加一个包含上一个事件的 id 的列。数据应根据 pid（自定义顺序，其中 157 < 598 < 118 < 783）和 sid 排序。棘手的部分是有些事件有 11 行，有些只有 1 行。
other_columns 代表所有其他应该保留的列。
我尝试使用 LAG() window 具有预先计算的偏移量的函数，如下所示：
WITH example_tbl_with_offset AS (
SELECT * FROM example_tbl
LEFT JOIN (SELECT id, COUNT(id)::int AS lag_offset
FROM example_tbl
GROUP BY id) AS offset_tbl
USING (id)
)
SELECT
*,
LAG(id, lag_offset) OVER (PARTITION BY tid
ORDER BY (CASE
WHEN pid = 157 THEN 1
WHEN pid = 598 THEN 2
WHEN pid = 118 THEN 3
WHEN pid = 783 THEN 4
END, sid
)) AS prev_id
FROM example_tbl_with_offset;
然而，尽管 prev_id 列似乎对前几个事件有效，但它最终失去了踪迹。
预期输出附在下面：
CREATE TABLE expected_output (
id CHAR(1),
pid INT,
sid INT,
tid VARCHAR(10),
prev_id CHAR(1)
)
INSERT INTO expected_output (id, pid, sid, tid, prev_id)
VALUES
('Q', 157, 81, 'A62', NULL),
('Q', 157, 81, 'A62', NULL),
('Q', 157, 81, 'A62', NULL),
('Q', 157, 81, 'A62', NULL),
('Q', 157, 81, 'A62', NULL),
('Q', 157, 81, 'A62', NULL),
('Q', 157, 81, 'A62', NULL),
('Q', 157, 81, 'A62', NULL),
('Q', 157, 81, 'A62', NULL),
('Q', 157, 81, 'A62', NULL),
('Q', 157, 81, 'A62', NULL),
('c', 157, 85, 'A32', NULL),
('c', 157, 85, 'A32', NULL),
('c', 157, 85, 'A32', NULL),
('c', 157, 85, 'A32', NULL),
('c', 157, 85, 'A32', NULL),
('c', 157, 85, 'A32', NULL),
('c', 157, 85, 'A32', NULL),
('c', 157, 85, 'A32', NULL),
('c', 157, 85, 'A32', NULL),
('c', 157, 85, 'A32', NULL),
('c', 157, 85, 'A32', NULL),
('r', 598, 16, 'A32', 'c'),
('Z', 598, 44, 'A62', 'Q'),
('w', 598, 49, 'A32', 'r'),
('f', 598, 51, 'A62', 'Z'),
('T', 118, 17, 'A62', 'f'),
('s', 118, 18, 'A62', 'T'),
('v', 118, 22, 'A32', 'w'),
('H', 118, 23, 'A32', 'v'),
('H', 118, 23, 'A32', 'v'),
('H', 118, 23, 'A32', 'v'),
('H', 118, 23, 'A32', 'v'),
('H', 118, 23, 'A32', 'v'),
('H', 118, 23, 'A32', 'v'),
('H', 118, 23, 'A32', 'v'),
('H', 118, 23, 'A32', 'v'),
('H', 118, 23, 'A32', 'v'),
('H', 118, 23, 'A32', 'v'),
('H', 118, 23, 'A32', 'v'),
('y', 118, 33, 'A62', 's'),
('l', 118, 35, 'A32', 'H'),
('m', 118, 37, 'A62', 'y'),
('G', 118, 38, 'A32', 'I'),
('F', 118, 41, 'A32', 'G'),
('B', 118, 43, 'A62', 'm'),
('u', 118, 48, 'A62', 'B'),
('J', 118, 54, 'A32', 'F'),
('z', 118, 55, 'A32', 'J'),
('a', 118, 59, 'A32', 'z'),
('h', 118, 60, 'A62', 'u'),
('n', 118, 63, 'A32', 'a'),
('p', 118, 72, 'A32', 'n'),
('Y', 118, 75, 'A32', 'p'),
('N', 118, 79, 'A62', 'h'),
('R', 118, 86, 'A62', 'N'),
('R', 118, 86, 'A62', 'N'),
('R', 118, 86, 'A62', 'N'),
('R', 118, 86, 'A62', 'N'),
('R', 118, 86, 'A62', 'N'),
('R', 118, 86, 'A62', 'N'),
('R', 118, 86, 'A62', 'N'),
('R', 118, 86, 'A62', 'N'),
('R', 118, 86, 'A62', 'N'),
('R', 118, 86, 'A62', 'N'),
('R', 118, 86, 'A62', 'N'),
('I', 118, 89, 'A62', 'R'),
('U', 118, 90, 'A32', 'Y'),
('U', 118, 90, 'A32', 'Y'),
('U', 118, 90, 'A32', 'Y'),
('U', 118, 90, 'A32', 'Y'),
('U', 118, 90, 'A32', 'Y'),
('U', 118, 90, 'A32', 'Y'),
('U', 118, 90, 'A32', 'Y'),
('U', 118, 90, 'A32', 'Y'),
('U', 118, 90, 'A32', 'Y'),
('U', 118, 90, 'A32', 'Y'),
('U', 118, 90, 'A32', 'Y'),
('O', 118, 93, 'A32', 'U'),
('V', 783, 11, 'A62', 'I'),
('x', 783, 27, 'A32', 'O'),
('i', 783, 61, 'A62', 'V'),
('i', 783, 61, 'A62', 'V'),
('i', 783, 61, 'A62', 'V'),
('i', 783, 61, 'A62', 'V'),
('i', 783, 61, 'A62', 'V'),
('i', 783, 61, 'A62', 'V'),
('i', 783, 61, 'A62', 'V'),
('i', 783, 61, 'A62', 'V'),
('i', 783, 61, 'A62', 'V'),
('i', 783, 61, 'A62', 'V'),
('i', 783, 61, 'A62', 'V');
以下顺序可能更容易理解实际逻辑：
SELECT * FROM expected_output
ORDER BY tid, CASE
WHEN pid = 157 THEN 1
WHEN pid = 598 THEN 2
WHEN pid = 118 THEN 3
WHEN pid = 783 THEN 4
END, sid;
@编辑：我的PostgreSQL版本是9.5.
这是有效的，希望有人能找到更好的解决方案
select m.* from (
select *, lag(id,1) over ( PARTITION BY tid
order by (CASE
WHEN pid = 157 THEN 1
WHEN pid = 598 THEN 2
WHEN pid = 118 THEN 3
WHEN pid = 783 THEN 4
END, sid
)
) from ( select distinct * from example_tbl et )a )
m,
example_tbl n
where m.id = n.id and m.pid = n.pid and m.sid = n.sid and m.tid = n.tid
order by (CASE
WHEN m.pid = 157 THEN 1
WHEN m.pid = 598 THEN 2
WHEN m.pid = 118 THEN 3
WHEN m.pid = 783 THEN 4
END, m.sid
)
类似的解决方案：
with
a as (
select distinct *,
case
WHEN pid = 157 THEN 1
WHEN pid = 598 THEN 2
WHEN pid = 118 THEN 3
WHEN pid = 783 THEN 4
end as cat
from example_tbl
),
b as (
select id, cat,
lag(id, 1) over(partition by tid order by cat, sid) prev_id
from a
)
select c.*, b.prev_id
from example_tbl c
left join b using (id)
order by b.cat,c.sid
Postgres 11 的主要新特性之一在 release notes:
中是这样宣传的
- Window functions now support all framing options shown in the SQL:2011 standard, including
RANGEdistancePRECEDING/FOLLOWING,GROUPSmode, and frame exclusion options
使用这个，有一个解决方案 single window function in a 单身SELECT:
SELECT *, first_value(id) OVER (PARTITION BY tid
ORDER BY CASE pid
WHEN 157 THEN 1
WHEN 598 THEN 2
WHEN 118 THEN 3
WHEN 783 THEN 4
END, sid
GROUPS BETWEEN 1 PRECEDING AND 1 PRECEDING
) AS prev_id
FROM example_tbl;
db<>fiddle here
应该也表现不错。
也适用于您的扩展测试设置，但不适用于版本 11 之前的 Postgres。
In
GROUPSmode, the offset again must yield a non-null, non-negative integer, and the option means that the frame starts or ends the specified number of peer groups before or after the current row's peer group, where a peer group is a set of rows that are equivalent in theORDER BYordering.
所选的框架定义GROUPS BETWEEN 1 PRECEDING AND 1 PRECEDING完全符合您的需要。
您的描述和测试数据似乎暗示 sid 和 id 的变化是一致的。所以 window 框架只包含一个 id 值。 min() 或 max() 也可以，但我选择 first_value() 是最便宜的。而且因为它适用于任何数据类型，即使 min() 或 max() 会失败（如 json）。
此外，使用更短（并且稍微便宜）的“简单”或“转换”CASE。参见：
- Display column name with max value between several columns
对于 Postgres 9.5
这适用于您过时的 Postgres 9.5 版：
SELECT e.*, p.prev_id
FROM example_tbl e
JOIN (
SELECT *
, lag(id) OVER (PARTITION BY tid
ORDER BY CASE pid
WHEN 157 THEN 1
WHEN 598 THEN 2
WHEN 118 THEN 3
WHEN 783 THEN 4
END, sid) AS prev_id
FROM (
SELECT DISTINCT ON (tid, pid, sid)
tid, pid, sid, id
FROM example_tbl
) dist
) p USING (tid, pid, sid);
db<>fiddle here
这是假设 tid、pid、sid 被定义为 NOT NULL。否则，你需要做更多。
使用
(tid, pid, sid)的不同组合得出 table。同样，id只是一个负载列。关于DISTINCT ON:- Select first row in each GROUP BY group?
现在，具有默认 window 框架的
lag()完成了从“前一”行获取id的工作。加入完整table。