พยายาม หาคำตอบสั้นๆ ที่จะเขียนคำสั่งให้การ count ได้ค่า 0 มาแสดงด้วย

select case when count(*) >0 then count(*) else 0 end result from table_name

SELECT
co_office.distid AS `รหัสอำเภอ`,
co_office.cup_code AS `รหัสcup`,
co_office.off_id AS `รหัสสถานบริการ`,
co_office.off_name AS `ชื่อสถานบริการ`,
case when 
Count(DISTINCT chronic.cid,chronic.pcucode,chronic.pid)>0
 then Count(DISTINCT chronic.cid,chronic.pcucode,chronic.pid) 
else 0 end `จำนวนผู้ป่วยเบาหวาน` 
FROM
chronic
LEFT OUTER JOIN co_office ON chronic.pcucode = co_office.off_id
INNER JOIN labfu ON chronic.pcucode = labfu.pcucode AND chronic.pid = labfu.pid
WHERE
chronic.chronic BETWEEN 'E10' AND 'E149'
GROUP BY
co_office.off_id
ORDER BY
`รหัสอำเภอ` ASC,
`รหัสcup` ASC,
`รหัสสถานบริการ` ASC

SELECT
distid AS DistID,
cup_code AS Cup,
off_id AS Hoscode,
off_name AS Hosname,

(SELECT
Count(DISTINCT chronic.cid,chronic.pcucode,chronic.pid) AS `จำนวนผู้ป่วยเบาหวาน`
FROM
chronic
#LEFT OUTER JOIN co_office ON chronic.pcucode = co_office.off_id
INNER JOIN labfu ON chronic.pcucode = labfu.pcucode AND chronic.pid = labfu.pid
WHERE
chronic.chronic BETWEEN 'E10' AND 'E149'
GROUP BY
o.off_id)

FROM
co_office o
WHERE LENGTH(cup_code) = 5
GROUP BY
off_id