Usage of SQL Server database distinct

Distinct: Used to filter duplicate records. It is often used only to return the number of non-repeating records, rather than using it to return all values that are not re-recorded. The reason is that distinct only with double-loop query to solve, and so for a very large number of stations, will undoubtedly directly affect the efficiency.

Form Name table

Id	NAME
1	A
2	B
3	B
4	C

1. Example: Query the name for all data that is not duplicated. Note: Distinct must be placed at the beginning

Select distinct  from Table

A

B

C

2. Query the name for all data that is not duplicated, including the ID.

Select distinct  from Table

1	A
2	B
3	B
4	C

So it's important to note that there are multiple fields behind the distinct, which are multi-conditional, and are duplicates only when these conditions are the same.

3. Want to get the following results how to write SQL

1	A
2	B
4	C

Select *   from Table Group  by name

Summarize:

Distinct is used to go heavy.

Must be placed in the first after the select

Multiple fields behind distinct are multi-conditional deduplication, which is the only way to duplicate records if these conditions are the same.

Usage of SQL Server database distinct