Again it is the unknown value of NULL. Just as it is unknown if NULL 3. Alice is excluded from the results. But it is less than or equal to 5, so he is now included in the query result.
Once again, Alice is excluded from the results. You should now be clear that this can only result in a value of unknown. They return only true or false and are the best practice for incorporating NULL values into your queries. This is a more advanced topic. But this can sometimes be an inefficient way of achieving a result. Let's look at an example that demonstrates this.
You can run it yourself using this SQL Fiddle. Here's a guide to more sites to use for SQL practice. Just focus on what each query returns, starting with this one:. It looks good, but we have 3 customers. It will include every row in the left table of the FROM statement even if there is no matching data in the right table.
This gives us our next query:. Where there is no matching row in the right table, the columns are filled with NULLs. The way to fix this is to move the conditional expression, here o.
Good Luck! Krishna Chavali Krishna Chavali 11 2 2 bronze badges. Chameleon Chameleon 2 2 silver badges 8 8 bronze badges. Donald Duck 7, 19 19 gold badges 67 67 silver badges 87 87 bronze badges. Chandan Kumar Chandan Kumar 1 1 1 bronze badge.
Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Podcast Making Agile work for data science. Stack Gives Back Featured on Meta. New post summary designs on greatest hits now, everywhere else eventually. Visit chat. Linked 0. See more linked questions. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Asked 11 years, 2 months ago. Active 3 years, 6 months ago. Viewed 28k times. Improve this question. Incognito Incognito Those are two different queries which will return different results.
This might be good to know but remember that premature optimization is the root of all evil. Both ways could work, depending on your requirements. Pick one. Either method will most definitly not be your performance problem if you have one to begin with. Are you guaranteed that your select will always return 0 or 1 results?
You'll get an error if the query returns more than 1 row. Joe ID is primary key, so there can't be multiple values. Show 2 more comments. Active Oldest Votes. What you should do is this.
END And did you actually mean equals 0?
0コメント