MYSQL查询中的多个计数

Question

I would like to count a specific database column with TWO different count criteria so i can calculate a percentage

For example lets same the database column is called Latency, and the data in the column contains the number of seconds.

I would like to count the number of Latency messages > 50 seconds but also the TOTAL number of Latency messages in the same query ( ie > 0 seconds)

My current query for > 50 seconds is as follows

select COUNT(*) from table WHERE date = 20180701 and CAST(Latency As Signed) > 50

How would i include counts > 0 seconds in the same query ??

Answer 1

Use conditional aggregation:

SELECT
    COUNT(CASE WHEN CAST(Latency As Signed) > 50 THEN 1 END) AS latency,
    COUNT(CASE WHEN CAST(Latency As Signed) > 0  THEN 1 END) AS total,
    100.0 * COUNT(CASE WHEN CAST(Latency As Signed) > 50 THEN 1 END) /
            COUNT(CASE WHEN CAST(Latency As Signed) > 0  THEN 1 END) AS percentage
FROM table
WHERE date = 20180701;

Answer 2

This maybe helpful to you, @John, How to get multiple counts with one SQL query? It uses count together with aggregate functions in order to target multiple count function in one query..