空白表返回mysql_num_rows（$ result）= 1 [关闭]

Question

my query is

 $result=SELECT MAX(surveyID) as surveyID  FROM `sg_count`WHERE userID=$user

where sg_count table has no records

but mysql_num_rows($result) returns 1.

Answer 1

Aggregating functions like max and count will return one row (without a grouping clause), that's their nature.

By way of example, count(*) on an empty table will give you one row with the value 0.

I suspect, although I haven't tried, that you'll be getting a single row in your query with a NULL value. That's how all the other DBs I've used handle it. Assuming the column is non-NULL specified, you can use that return value to detect the "no row" case. Even if it allows NULLs, that may still be workable, it depends on what you want to do in that case.

Otherwise, you're probably better off checking the count as well with something like:

select   count(*) as quant,
         max(surveyID) as surveyID
from     sg_count
where    userID = 'somebody'

Then, if quant is zero, you know there were no rows. If it's non-zero, there were rows and the maximum value of surveyID is in the other column.