我有以下sql：
SELECT STRFTIME('%m',date) ord,CASE STRFTIME('%m',date) WHEN '01' THEN 'January'
WHEN '02' THEN 'Febuary'
WHEN '03' THEN 'March'
WHEN '04' THEN 'April'
WHEN '05' THEN 'May'
WHEN '06' THEN 'June'
WHEN '07' THEN 'July'
WHEN '08' THEN 'August'
WHEN '09' THEN 'September'
WHEN '10' THEN 'October'
WHEN '11' THEN 'November'
WHEN '12' THEN 'December'
ELSE '' END AS month,count(*) AS count
FROM events
WHERE type='Birth' AND
date <> ''
GROUP BY month,ord
ORDER BY ord
这给我的结果类似于：
ord month count 01 January 1 02 Febuary 1 03 March 3 05 May 4 07 July 2 08 August 2 09 September 2 11 November 4
但正如你所看到的,它有差距.有没有办法用0计数来填补缺失的月份？
解决方法
研究外连接.
运行以下一次：
CREATE TABLE months (
mm char(2),name char(10)
);
INSERT INTO months VALUES ('01','January');
INSERT INTO months VALUES ('02','Febuary');
INSERT INTO months VALUES ('03','March');
INSERT INTO months VALUES ('04','April');
INSERT INTO months VALUES ('05','May');
INSERT INTO months VALUES ('06','June');
INSERT INTO months VALUES ('07','July');
INSERT INTO months VALUES ('08','August');
INSERT INTO months VALUES ('09','September');
INSERT INTO months VALUES ('10','October');
INSERT INTO months VALUES ('11','November');
INSERT INTO months VALUES ('12','December');
运行这个：
SELECT m.mm AS ord,m.name AS month,count(e.date) AS count
FROM months m LEFT OUTER JOIN events e
ON strftime('%m',e.date) = m.mm
WHERE e.type='Birth' AND
e.date <> ''
GROUP BY month,ord
ORDER BY ord;
