sql - 如果序列中的另一行不遵循 SQL Server，如何返回一行

Question

我有以下场景，我能想到的唯一方法是将所有数据拉回临时表，然后使用游标循环遍历它，根据当前记录更新记录或最后一条记录。

基本上，如果发生称为澄清的操作，我想返回此记录，但如果在澄清之后发生澄清保留，那么我不希望返回澄清。

现在的问题是，在没有澄清保留的情况下，任何数量的澄清都可能连续发生，所以如果发生 5 次澄清，然后有 1 次保留，我想返回 4 条记录。保留之后也可以进行澄清，在这种情况下，我想显示澄清。

有人对比光标更好的解决方案有任何建议吗？

Answer 1

我已经对您的数据结构做出了假设，但该理论仍应适用于您

-- Example table
DECLARE @t table (
   action_description   char(20)
 , when_occured         datetime
);

-- Set up data
INSERT INTO @t (action_description, when_occured)
  VALUES ('clarification'     , DateAdd(mi, -9, Current_Timestamp)) -- Include
       , ('clarification'     , DateAdd(mi, -8, Current_Timestamp)) -- Include
       , ('clarification'     , DateAdd(mi, -7, Current_Timestamp)) -- Include
       , ('clarification'     , DateAdd(mi, -6, Current_Timestamp))
       , ('clarification hold', DateAdd(mi, -5, Current_Timestamp))
       , ('clarification'     , DateAdd(mi, -4, Current_Timestamp)) -- Include
       , ('clarification'     , DateAdd(mi, -3, Current_Timestamp)) -- Include
       , ('clarification'     , DateAdd(mi, -2, Current_Timestamp)) -- Include
       , ('clarification'     , DateAdd(mi, -1, Current_Timestamp)) -- Include
       , ('clarification'     , DateAdd(mi,  0, Current_Timestamp)) -- Include
       , ('clarification'     , DateAdd(mi, +1, Current_Timestamp))
       , ('clarification hold', DateAdd(mi, +2, Current_Timestamp))
       , ('clarification'     , DateAdd(mi, +3, Current_Timestamp)) -- Include
       , ('clarification'     , DateAdd(mi, +4, Current_Timestamp))
       , ('clarification hold', DateAdd(mi, +5, Current_Timestamp))
       , ('clarification hold', DateAdd(mi, +6, Current_Timestamp))
       , ('clarification'     , DateAdd(mi, +7, Current_Timestamp)) -- Include
       , ('clarification'     , DateAdd(mi, +8, Current_Timestamp))
       , ('clarification hold', DateAdd(mi, +9, Current_Timestamp));

; WITH all_actions AS (
  SELECT action_description
       , when_occured
       , Row_Number() OVER (ORDER BY when_occured) As row_num -- Provide a sequence for joining
  FROM   @t
)
SELECT a1.action_description
     , a1.when_occured
FROM   all_actions As a1
 LEFT
  JOIN all_actions As a2                            -- Join back to self
    ON a2.row_num = a1.row_num + 1                  -- on previous row
   AND a2.action_description = 'clarification hold' -- where the previous row had this action
WHERE  a1.action_description = 'clarification' -- Only want to show clarification actions
AND    a2.action_description IS NULL           --  and exclude those who had a row in the join