Select SQL 查询中的 2 列不同

Question

If I have a table such as

1 bob
1 ray
1 bob
1 ray
2 joe
2 joe

And I want to select distinct based on the two columns so that I would get

1 bob
1 ray
2 joe

How can I word my query? Is the only way to concatenate the columns and wrap them around a distinct function operator?

Answer 1

select distinct id, name from [table]

要么

select id, name from [table] group by id, name

Answer 2

You can just do:

select distinct col1, col2 from your_table;

That's exactly what the distinct operator is for: removing duplicate result rows.

Keep in mind that distinct is usually a pretty expensive operation, since, after processing the query, the DB server might perform a sort operation in order to remove the duplicates.

Answer 3

@Pablo Santa Cruz: it does not remove duplicates from any columns.

SELECT DISTINCT prof1, prof2 
FROM programmer

Results in:

ASSEMBLY    C
CLIPPER COBOL
COBOL   DBASE
PASCAL  BASIC
PASCAL  CLIPPER
PASCAL  DBASE