当我更新表时，如何将count（）作为条件？

Question

SELECT COUNT(TableID) 
FROM DiningTable
WHERE IsAvail = 1;

我可以在逻辑上得到“Number of Table”，但我想在下一个sql查询中使用该数字。

UPDATE DiningTable
SET IsAvail = 0
WHERE TableID = 11 - [Should be the number of Table, the result I get above];

我该怎么办？

Answer 1

如果第一个选择返回0行，请确保将isnull（）检查以避免出现空错误

UPDATE DiningTable
SET IsAvail = 0
WHEN TableID = 11 - (SELECT ISNULL(COUNT(TableID),0) FROM DiningTable WHERE IsAvail = 1);

Answer 2

UPDATE DiningTable
SET IsAvail = 0
WHEN TableID = 11 - (SELECT COUNT(TableID) FROM DiningTable WHERE IsAvail = 1);