SQL-计算列中的出现次数

Question

I would like to count values in a column (col2) that contains strings so that the a new column (count) returns the number of strings.

For example:

col1 | col2 | count
1    | dog  |  1
2    | cat  |  2
3    | cat  |  2
4    | bird |  1

...

Answer 1

Standard SQL offers window functions that do this:

select col1, col2, count(*) over (col2) as cnt
from t;

Answer 2

If, you are working with Microsoft SQL Server, then you could use below SQL Script

SELECT col1,
       col2,
       COUNT(col2) OVER(PARTITION BY col2) AS cnt
FROM <table_name>
ORDER BY col1;

Result :

col1 col2   cnt
1    dog    1
2    cat    2
3    cat    2
4    bird   1