How to fill date gaps in MySQL? - sql

Question

How i can fill date gaps in MySQL? Here is my query:
SELECT DATE(posted_at) AS date,
COUNT(*) AS total,
SUM(attitude = 'positive') AS positive,
SUM(attitude = 'neutral') AS neutral,
SUM(attitude = 'negative') AS negative
FROM `messages`
WHERE (`messages`.brand_id = 1)
AND (`messages`.`spam` = 0
AND `messages`.`duplicate` = 0
AND `messages`.`ignore` = 0)
GROUP BY date ORDER BY date
It returns proper result set - but i want to fill gaps between dates start and end by zeros. How i can do this?

Answer 1

You'll need to create a helper table and fill it with all dates from start to end, then just LEFT JOIN with that table:
SELECT d.dt AS date,
COUNT(*) AS total,
SUM(attitude = 'positive') AS positive,
SUM(attitude = 'neutral') AS neutral,
SUM(attitude = 'negative') AS negative
FROM dates d
LEFT JOIN
messages m
ON m.posted_at >= d.dt
AND m.posted_at < d.dt + INTERVAL 1 DAYS
AND spam = 0
AND duplicate = 0
AND ignore = 0
GROUP BY
d.dt
ORDER BY
d.dt
Basically, what you need here is a dummy rowsource.
MySQL is the only major system which lacks a way to generate it.
PostgreSQL implements a special function generate_series to do that, while Oracle and SQL Server can use recursion (CONNECT BY and recursive CTEs, accordingly).

Answer 2

I don't know whether MySQL will support the following/similar syntax; but if not, then you could just create and drop a temporary table.
--Inputs
declare #FromDate datetime, /*Inclusive*/
#ToDate datetime /*Inclusive*/
set #FromDate = '20091101'
set #ToDate = '20091130'
--Query
declare #Dates table (
DateValue datetime NOT NULL
)
set NOCOUNT ON
while #FromDate <= #ToDate /*Inclusive*/
begin
insert into #Dates(DateValue) values(#FromDate)
set #FromDate = #FromDate + 1
end
set NOCOUNT OFF
select dates.DateValue,
Col1...
from #Dates dates
left outer join SourceTableOrView data on
data.DateValue >= dates.DateValue
and data.DateValue < dates.DateValue + 1 /*NB: Exclusive*/
where ...?