这是我想对MySQL数据库做的。
我想做的是:
SELECT *
FROM itemsOrdered
WHERE purchaseOrder_ID = '@purchaseOrdered_ID'
AND status = 'PENDING'
如果不返回任何行，则可以通过If (dr。HasRows == false)，我现在将在purchaseOrder数据库中创建一个UPDATE:
UPDATE purchaseOrder
SET purchaseOrder_status = 'COMPLETED'
WHERE purchaseOrder_ID = '@purchaseOrder_ID'
我怎样才能缩短这个过程呢?
当前回答
Select FROM t1
WHERE s11 > ANY
(SELECT col1,col2 FROM t2
WHERE NOT EXISTS
(SELECT * FROM t3
WHERE ROW(5*t2.s1,77)=
(SELECT 50,11*s1 FROM t4 UNION SELECT 50,77 FROM
(SELECT * FROM t5) AS t5)));
其他回答
Select FROM t1
WHERE s11 > ANY
(SELECT col1,col2 FROM t2
WHERE NOT EXISTS
(SELECT * FROM t3
WHERE ROW(5*t2.s1,77)=
(SELECT 50,11*s1 FROM t4 UNION SELECT 50,77 FROM
(SELECT * FROM t5) AS t5)));
在选择查询中，可以声明一个变量保存返回结果的数量。 然后，如果这个变量大于0，就可以运行update语句
Declare @ResultCount int
SELECT @ResultCount = count(*) FROM itemsOrdered WHERE purchaseOrder_ID = '@purchaseOrdered_ID' AND status = 'PENDING'
If @ResultCount > 0
UPDATE purchaseOrder SET purchaseOrder_status = 'COMPLETED' WHERE purchaseOrder_ID = '@purchaseOrder_ID'
因为MySQL不支持if exists(*Your condition*) (*Write Your query*)，你可以通过这样写来实现一个'if子句':
(*Write your insert or update query*) where not exists (*Your condition*)
if not exists(select top 1 fromFROM itemsOrdered
WHERE purchaseOrder_ID = '@purchaseOrdered_ID'
AND status = 'PENDING' )
Begin
UPDATE purchaseOrder
SET purchaseOrder_status = 'COMPLETED'
WHERE purchaseOrder_ID = '@purchaseOrder_ID
End
如果表包含数百万条记录，那么下面的查询将快速工作。
UPDATE PO
SET PO.purchaseOrder_status = 'COMPLETED'
FROM purchaseOrder PO
LEFT OUTER JOIN itemsOrdered IOD ON IOD.purchaseOrder_ID = PO.purchaseOrdered_ID and IOD.status = 'PENDING'
WHERE IOD.purchaseOrder_ID IS NULL
