表之間的資料匹配(生成交叉表)--sql
阿新 • • 發佈:2021-11-28
表之間的資料匹配(生成交叉表)--sql
建立表、新增資料
CREATE TABLE CourseMaster ( course_id int not null primary key, coures_name varchar(20) ); CREATE TABLE OpenCourses ( month int, course_id int not null , CONSTRAINT fk_course_id FOREIGN KEY (course_id) REFERENCES CourseMaster(course_id) ); insert into CourseMaster(course_id,coures_name) values (1,'會計入門 '), (2,'財務知識 '), (3,'簿記考試 '), (4,'稅務師 '); insert into OpenCourses(month,course_id) values (200706,1), (200706,3), (200706,1), (200706,4), (200707,4), (200708,2), (200708,4);
生成交叉表
我們要用這兩張表來生成交叉表,以便於一目瞭然地知道每個月開設的課程。
使用 IN 謂詞
-- 表的匹配 :使用 IN 謂詞 SELECT coures_name AS 課程名, CASE WHEN course_id IN (SELECT course_id FROM opencourses WHERE month = 200706) THEN 'o' ELSE 'x' END AS "6月", CASE WHEN course_id IN (SELECT course_id FROM opencourses WHERE month = 200707) THEN 'o' ELSE 'x' END AS "7月", CASE WHEN course_id IN (SELECT course_id FROM opencourses WHERE month = 200708) THEN 'o' ELSE 'x' END AS "8月" FROM coursemaster;
使用 EXISTS 謂詞
-- 表的匹配 :使用 EXISTS 謂詞 SELECT CM.coures_name AS 課程名, CASE WHEN EXISTS (SELECT course_id FROM opencourses oc WHERE month = 200706 AND oc.course_id=cm.course_id) THEN 'o' ELSE 'x' END as "6月", CASE WHEN EXISTS (SELECT course_id FROM opencourses oc WHERE month = 200707 AND oc.course_id=cm.course_id) THEN 'o' ELSE 'x' END as "7月", CASE WHEN EXISTS (SELECT course_id FROM opencourses oc WHERE month = 200708 AND oc.course_id=cm.course_id) THEN 'o' ELSE 'x' END as "8月" FROM coursemaster CM;