mysql - 三个条件的sql查询

Question

我有一个包含以下内容的表的数据库：

message_number  message_type   message_chat
     0                IN           Hi
     1                OB           Hello
     2                IN           Help
     3                IN           Want to find this thing
     4                OB           Sure
     5                OB           Please let me know

我写了 5 行，因为我想在我展示的示例表中的查询中合并我想要的所有可能的情况。

现在在我的查询输出中，我想要类似的东西：

message_in                                 message_out
  Hi                                         Hello
  Help                                        NULL
  Want to find this string                   Sure
     NULL                                  Please let me know

所以我想考虑的情况是：

1. 假设如果 message_number=0 和 message_number=1 都具有 message_type 值作为 IN 然后将 message_chat_in 作为 message_chat(at message_number=0) 和 message_chat 作为 NULL 并迭代 message_number=1

2. 如果 message_number =0 具有 message_type=IN 且 message_number =1 具有 message_type=OB，则将 message_chat(at message_number=0) 显示为 message_chat_in 并将 message_chat(at message_number=1) 显示为 message_out 并且不要迭代 message_number=1；

希望我已经澄清了条件，尽管我已经在预期的输出中包含了所有三个条件。我的 sqlquery 应该是什么样子？

编辑：我使用的是 mysql 版本 5.5.8

Answer 1

尝试以下查询

SELECT
  q1.message_number in_num,
  q1.message_chat in_chat,
  q2.message_number out_num,
  q2.message_chat out_chat
FROM
  (
    SELECT *,@i1:=IFNULL(@i1,0)+1 num
    FROM Chat
    ORDER BY message_number
  ) q1
LEFT JOIN
  (
    SELECT *,@i2:=IFNULL(@i2,0)+1 num
    FROM Chat
    ORDER BY message_number
  ) q2
ON q2.num=q1.num+1 AND q2.message_type<>q1.message_type
WHERE q1.message_type='IN'

UNION ALL

SELECT
  q1.message_number in_num,
  q1.message_chat in_chat,
  q2.message_number out_num,
  q2.message_chat out_chat
FROM
  (
    SELECT *,@i3:=IFNULL(@i3,0)+1 num
    FROM Chat
    ORDER BY message_number
  ) q1
RIGHT JOIN
  (
    SELECT *,@i4:=IFNULL(@i4,0)+1 num
    FROM Chat
    ORDER BY message_number
  ) q2
ON q2.num=q1.num+1 AND q2.message_type<>q1.message_type
WHERE q2.message_type='OB'
  AND q1.message_type IS NULL

ORDER BY IFNULL(in_num,out_num)

SQL 小提琴 - http://sqlfiddle.com/#!9/95a515/1

第二种变体

SET @i1 = 0;
SET @i2 = 0;
SET @i3 = 0;
SET @i4 = 0;

-- the same query

SQL 小提琴 - http://sqlfiddle.com/#!9/95a515/2

或者

SELECT 0,0,0,0 INTO @i1,@i2,@i3,@i4;

-- the same query

SQL 小提琴 - http://sqlfiddle.com/#!9/95a515/5

Answer 2

好的，由于 MySQL 中没有小于 8 的解析函数，代码可能不太容易理解：

with data_rn as
(
  -- this isolate consecutive rows with the same message_type
  select d1.*, count(d2.message_number) rn
  from data d1
  left join data d2 on d1.message_number > d2.message_number and d1.message_type != d2.message_type
  group by d1.message_number
),
data_rn2 as
(
    -- this marks the rows where new rows has to be added (i.e. when rn2 != 0)
    select d1.*, count(d2.message_number) rn2
    from data_rn d1
    left join data_rn d2 on d1.rn = d2.rn and d1.message_type = d2.message_type and d1.message_number > d2.message_number
    group by d1.message_number
), 
data_added as
(
    -- this add new rows
    select message_number, message_type, message_chat
    from data_rn2
    union all 
    select message_number - 0.5, 'OB', NULL from data_rn2 where message_type = 'IN' and rn2 != 0
    union all 
    select message_number - 0.5, 'IN', NULL from data_rn2 where message_type = 'OB' and rn2 != 0
    order by message_number
), data_added_rn as
(
    -- this compute new row numbering
    select d1.*, ceil((count(d2.message_number)+1)/2) rn 
    from data_added d1
    left join data_added d2 on d1.message_number > d2.message_number
    group by d1.message_number
)
-- this will do the final formating
select max(case when message_type = 'IN' then message_chat end) message_in,
       max(case when message_type = 'OB' then message_chat end) message_out
from data_added_rn
group by rn

演示

我试图适当地评论每个部分。

Answer 3

为什么不在这里使用分析函数？我会像这样用 Lead() 做到这一点：

with inc as ( 
--Do the incorporation in this block. could be subquery too 
--but its easier to read this way.

select 
case when message_type = 'IN' 
     then  message_chat 
     end as message_in

,case when LEAD(message_type) OVER (Order by message_number) = 'OB' --get the next message by number if it is type OB
    then LEAD(message_chat) OVER (order by message_number)   
    end as message_out
from input
)

select *
from inc 
where coalesce(message_in, message_out) is not null   --filter out rows where with in & out is null