SQL Select ALL ROWS 但仅当列值唯一时

Question

If I do the following:

select * from myTable

I get:

Column 1  | Column 2
---------------------
1         | Create
1         | Delete
2         | Create
3         | Create
4         | Create
4         | Delete
5         | Create

I want to perform a select statement where I only pull the rows that have a unique number for column 1

In otherwords I am looking for this result:

Column 1  | Column 2
---------------------
2         | Create
3         | Create
5         | Create

Not sure exactly how to pull this off with only one statement or if there even is a way to do that. Thanks!

Answer 1

You can use aggregation:

select col1, max(col2) as col2
from t
group by col1
having count(*) = 1;

If there is only one row for a given value of col1 , then max(col2) will be the value of the column on that row.

Answer 2

If there are not duplicate (column1, column2) tuples, one option is not exists :

select t.*
from mytable t
where not exists (
    select 1 from mytable t1 where t1.column1 = t.column1 and t1.column2 <> t.column2
)

Answer 3

A simple query to limit column #1 entires w/ a count not equal to 1.

SELECT col1, COUNT(col1), col2 
FROM myTable
WHERE count(col1) = 1
GROUP BY col1

Answer 4

Select column1, column2 from (select column1, column2, count(column1) over (PARTITION BY column2) count
from myTable) where count = 1

Answer 5

you can use group by =

select * from myTable where empno in (select empno val from myTable group by empno having COUNT(*) =1 )