What is the difference between UNION and UNION ALL?

1.	What is the difference between UNION and UNION ALL?
Answer» UNION blends the contents of two structurally-compatible TABLES into a solitary joined table. The distinction among UNION and UNION ALL is that UNION will discard duplicate records through UNION ALL will incorporate duplicate records. Note that the presentation of UNION ALL will commonly be superior to UNION since UNION requires the server to do the extra WORK of expelling any duplicate. In this way, in SITUATIONS where there is a SURETY that there won't be any copies, or where having copies isn't an issue, utilization of UNION ALL eventual suggested for performance reasons. Let's have a look at the below examples explaining the USAGE of both. In the first, we have used UNION and in the second we have explained UNION ALL.

Answer»

UNION blends the contents of two structurally-compatible TABLES into a solitary joined table. The distinction among UNION and UNION ALL is that UNION will discard duplicate records through UNION ALL will incorporate duplicate records. Note that the presentation of UNION ALL will commonly be superior to UNION since UNION requires the server to do the extra WORK of expelling any duplicate. In this way, in SITUATIONS where there is a SURETY that there won't be any copies, or where having copies isn't an issue, utilization of UNION ALL eventual suggested for performance reasons. Let's have a look at the below examples explaining the USAGE of both. In the first, we have used UNION and in the second we have explained UNION ALL.

Discussion

No Comment Found

Related InterviewSolutions

What is .TUF file? What is the significance of the same? Any implications if the file is deleted?
Full backup size is 300 GB, usually my diff backup size varies between 300 MB and 5 GB, unfortunately, one-day diff backup size was increased to 250 GB? What might be the reason any idea?
See I have an environment, Sunday night full backup, everyday night diff backup, and every 45 min a transactional backup. The disaster happened at 2:30 PM on Saturday. You suddenly found that the last Sunday backup has been corrupted. What’s your recovery plan?
I wanted to know what are the maximum worker threads setting and active worker thread count on SQL server. Can you tell me how to capture this info? What’s the default value for the max thread count?
How distributed transactions work in SQL Server?
Can we add an article to the existing publication without generating a snapshot with all articles?
Consider a situation where publisher database log file has been increasing and there is just a few MB available on disk. As an experienced professional how do you react to this situation? Remember no disk space available and also we can’t create a new log file on another drive
When should a developer use the NOLOCK hint? What problems can happen when using this hint and how can these problems be addressed?
What is an optimistic and pessimistic lock in SQL?
What is Lock escalation in SQL