Using COUNT CASE WHEN MONTH Statement in MariaDB 10.2.15 - sql

Question

I created a query to calculate the Amount of Id in a table using COUNT, CASE, WHEN and MONTH ..
Code:
SELECT
COUNT(CASE WHEN MONTH(LogsFormatted.DateIn) = 1 THEN LogsFormatted.Id ELSE 0 END ) AS '1',
COUNT(CASE WHEN MONTH(LogsFormatted.DateIn) = 2 THEN LogsFormatted.Id ELSE 0 END ) AS '2'
FROM
HrAttLogsFormatted AS LogsFormatted
WHERE
LogsFormatted.DateIn BETWEEN '2019-01-01' AND '2019-02-31'
AND LogsFormatted.Late != ''
Output :
| 1 | 2 |
| 1378 | 1378 |
The output I want to make is to calculate the Id in each month, namely Month 1 and Month 2
| 1 | 2 |
| 792 | 586 |
The data above is a fact
Using the above query instead adds up between the results of calculating month 1 and month 2

Answer 1

You should be counting NULL when the criteria in your CASE expression does not match. Also, I prefer counting 1 unless you really want to the count the Ids themselves. This version should work:
SELECT
COUNT(CASE WHEN MONTH(lf.DateIn) = 1 THEN 1 END) AS '1',
COUNT(CASE WHEN MONTH(lf.DateIn) = 2 THEN 1 END) AS '2'
FROM HrAttLogsFormatted AS lf
WHERE
lf.DateIn BETWEEN '2019-01-01' AND '2019-02-31' AND
lf.Late != '';
Note carefully that the current counts you are seeing sum up to the individual counts, that is:
1378 = 792 + 586
The reason for this is the the COUNT function "counts" any non NULL value as 1, and any NULL value as zero. Your current CASE expression will always count 1, for every record in the table.

Answer 2

remove else part from case when expression - if you use else with 0 then count takes that also in consideration which gives u actually wrong ouput
SELECT
COUNT(CASE WHEN MONTH(LogsFormatted.DateIn) = 1 THEN LogsFormatted.Id END ) AS '1',
COUNT(CASE WHEN MONTH(LogsFormatted.DateIn) = 2 THEN LogsFormatted.Id END ) AS '2'
FROM
HrAttLogsFormatted AS LogsFormatted
WHERE
LogsFormatted.DateIn BETWEEN '2019-01-01' AND '2019-02-31'
AND LogsFormatted.Late != ''

Answer 3

If you are using MariaDB, I would just use SUM() with a boolean:
SELECT SUM( MONTH(lf.DateIn) = 1 ) as month_1,
SUM( MONTH(lf.DateIn) = 2 ) as month_2
FROM HrAttLogsFormatted lf
WHERE lf.DateIn >= '2019-01-01' AND
lf.DateIn < '2020-01-01' AND
lf.Late <> '';
This assumes that the id that you are counting is never NULL (a reasonable assumption for an id).
Note other changes:
The column aliases do not need to be escaped. Don't use non-standard names, unless you need them -- for some reason -- for downstream processing.
This uses a shorter table alias, so the query is easier to write and to read.
The date comparisons use inequalities, so this works both for dates and datetimes.
<> is the standard SQL comparison operator for inequality.