[英]SQL do inner join if condition met
我想要一個改善我的SQL代碼的好方法,我必須在滿足條件時使用內連接。 我目前正在復制代碼:
@SystemMerge bit
if (@SystemMerge=1)
BEGIN
SELECT
.......
FROM myTable
INNER JOIN table ON table.param1=myTable.param1
INNER JOIN systemTable on systemTable.param2=myTable.param2
END
ELSE
BEGIN
SELECT
.......
FROM myTable
INNER JOIN table ON table.param1=myTable.param1
END
我想以這樣的方式做到這一點:
@SystemMerge bit
BEGIN
SELECT
.......
FROM myTable
INNER JOIN table ON table.param1=myTable.param1
***//the next 4 lines is not working, but this pseudo of what i want:***
if (@SystemMerge=1)
begin
INNER JOIN systemTable on systemTable.param2=myTable.param2
end
編輯:解決方案(感謝@Damien_The_Unbeliever):
LEFT JOIN systemTable ON systemTable.param2=myTable.param2
WHERE
((@SystemMerge=1 AND systemTable.param2 is not null)
OR
(@SystemMerge=0 OR @SystemMerge is null))
這應該(近似地)做同樣的事情:
SELECT
.......
FROM myTable
INNER JOIN table ON table.param1=myTable.param1
LEFT JOIN systemTable on systemTable.param2=myTable.param2 and @SystemMerge = 1
WHERE (@SystemMerge = 0 OR systemTable.NonNullableColumn IS NOT NULL)
當然,這也意味着必須編寫對systemTable
列的任何其他引用,以期望這些systemTable
NULL
。
動態sql怎么樣?
declare @sel varchar(max)
set @sel = ' SELECT
.......
FROM myTable
INNER JOIN table ON table.param1=myTable.param1
'
if (@SystemMerge=1)
begin
set @sel = @sel+'INNER JOIN systemTable on systemTable.param2=myTable.param2'
end
exec(@sel)
如果我是對的簡單方法 -
SELECT
.......
FROM myTable
INNER JOIN table ON table.param1 = myTable.param1
INNER JOIN systemTable on @SystemMerge = 0 or systemTable.param2=myTable.param2
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.