SQL内部联接两个表，右侧有2个匹配项

Question

I have two tables like this:

I want to select In and Out values from log details where id=1 in log table. I tried this for In value:

SELECT Log.Time, LogDetail.Value
FROM Log where ID=1
INNER JOIN LogDetail
ON Log.ID=LogDetail.ID where Name="In";

Is this a true query?

Answer 1

If you will try to run this query - you will see it can't be executed. The reason is two where statements it contains.

Query can contain only one where statement in most DBMS (while this statement can contain multiple conditions joined together by logical operators).

Also it is better to use table aliases - this makes query more readable and prevents possible ambiguities.

So your query should look like:

select L.Time, LD.Value
from Log as L
    inner join LogDetail as LD on L.ID=LD.ID 
where L.ID=1 and LD.Name="In"