基于条件

Question

添加/跳过哪里条款我有下面的查询，它从表变量中获取TagId列表并返回列表。

但我需要添加该CategoryId WHERE条件只有@Tags有记录。

只有当我的表变量有记录才能添加WHERE条件，否则运行1 = 1（总是为true）的相同查询并跳过类别过滤器？

DECLARE @TagIdList NVARCHAR(100) = '22,25,47' 
DECLARE @Tags TABLE (TagId INT); 

WITH CSVtoTable 
AS (
    SELECT CAST('<XMLRoot><RowData>' + REPLACE(t.val, ',', '</RowData><RowData>') + '</RowData></XMLRoot>' AS XML) AS x 
    FROM (
     SELECT @TagIdList 
     ) AS t(val) 
    ) 
INSERT INTO @Tags (TagId) 
SELECT m.n.value('.[1]', 'varchar(8000)') AS TagId 
FROM CSVtoTable 
CROSS APPLY x.nodes('/XMLRoot/RowData') m(n) 

SELECT BookingId 
    ,C.CategoryName 
FROM Booking B 
INNER JOIN Category C ON C.CategoryId = B.CategoryId 
WHERE (
     b.IsDeleted = 0 
     OR b.IsDeleted IS NULL 
     ) 
-- Add the below where condition only if @Tags has records, else use 1=1 
    AND C.CategoryId IN (
     SELECT DISTINCT CategoryId 
     FROM CategoryXTag con 
     WHERE TagId IN (
       SELECT TagId 
       FROM @Tags 
       ) 
     ) 

Answer 1

最终你只需要改变查询结束。如果性能是一个问题，您可能需要考虑在这两种情况下使用if块的两个分支，即使技术上可能将逻辑挤压到通常不会优化的单个查询中。

AND 
(
    C.CategoryId IN (
     SELECT CategoryId 
     FROM CategotryXTag 
     WHERE TagId IN (
      SELECT TagId 
      FROM @Tags 
     ) 
    ) 
    OR 
    (SELECT COUNT(*) FROM @Tags) = 0 
) 

Answer 2

declare int @tagcount = (select count(*) from @Tags); 

SELECT BookingId, C.CategoryName 
FROM Booking B 
INNER JOIN Category C 
     ON C.CategoryId = B.CategoryId 
     AND isnull(b.IsDeleted, 0) = 0 
INNER JOIN CategoryXTag con 
     ON C.CategoryId = con.CategoryId 
INNER JOIN @Tags tags 
     ON tags.TagID = con.TagID 
     OR @tagcount = 0; 

如果@tags是空的，你可能需要把一个记录它与永远不会被使用的值，然后或价值

if(@tagcount = 0) insert into @tags values (-100); 
or tags.TagID = -100; 

Answer 3

您无需修改​​您的where子句。相反，你运行你的最终查询之前填充@Tags每TagId从CategoryXTag达到同样的逻辑，如果@Tags是空的初始插件后：

if ((select count(*) from @Tags) = 0) 
    insert into @Tags 
    select distinct TagId 
    from CategoryXTag; 

Answer 4

我声明一个变量为@tags表：

declare @needTagsFilter bit 
set @needTagsFilter = case when exists(select 1 from @Tags) then 1 else 0 end 

和改变where子句等

AND (
    (@needTagsFilter = 0) OR 
    (C.CategoryId IN (
     SELECT DISTINCT CategoryId 
     FROM CategoryXTag con 
     WHERE TagId IN (
      SELECT TagId 
      FROM @Tags 
      ) 
    ) 
    ) 

COUNT（*）是慢然后存在。将count /直接添加到原始查询的缺点是SQL Server可能会为所有行执行它。