知识重点：
1.extract(day from schedule01::timestamp)=13
Extract 属于 SQL 的 DML(即数据库管理语言)函数，同样，InterBase 也支持 Extract，它主要用于从一个日期或时间型的字段内抽取年、月、日、时、分、秒数据，因此，它支持其关健字 YEAR、MONTH、DAY、HOUR、MINUTE、SECOND、WEEKDAY、YEARDAY。
Extract 的使用语法为：
EXTRACT(关健字 FROM 日期或时间型字段)
如：extract(year from schedule01)=2017从日期中提取年份
2.max()函数：取最大值
3.case()函数的嵌套
注意嵌套case()函数时，每个case的开始和结束。
排班功能：现有两个人员(A和B)，他们在不同日期的值班状态(state)不同，现在要查询他们在2017.6月的值班信息
表结构如下：
1 CREATE TABLE public.temp_schedule2
3 (4
5 id integer NOT NULL DEFAULT nextval('temp_schedule_id_seq'::regclass),6
7 schedule01 timestamp without time zone,--日期8
9 schedule03 character varying(255),--姓名10
11 state character varying(255),--值班状态(0休 1班)12
13 CONSTRAINT temp_schedule_pkey PRIMARY KEY (id)14
15 )
View Code
1.查询SQL语句：
1 select schedule03,schedule01,state fromtemp_schedule2
3 where extract(year from schedule01)=2017 and extract(month from schedule01)=6
4
5 order by schedule03,schedule01;
View Code
显示为：
2.现在需要根据(6月的)日期，从1号开始根据人员名称横向合并排列数据(即只显示两行)
显示效果如下：
实现的SQL语句如下：
1 select schedule03 asname2
3 ,max(case when extract(day from schedule01::timestamp)=1 then state end) asday14
5 ,max(case when extract(day from schedule01::timestamp)=2 then state end) asday26
7 ,max(case when extract(day from schedule01::timestamp)=3 then state end) asday38
9 ,max(case when extract(day from schedule01::timestamp)=4 then state end) asday410
11 ,max(case when extract(day from schedule01::timestamp)=5 then state end) asday512
13 ,max(case when extract(day from schedule01::timestamp)=6 then state end) asday614
15 ,max(case when extract(day from schedule01::timestamp)=7 then state end) asday716
17 ,max(case when extract(day from schedule01::timestamp)=8 then state end) asday818
19 ,max(case when extract(day from schedule01::timestamp)=9 then state end) asday920
21 ,max(case when extract(day from schedule01::timestamp)=10 then state end) asday1022
23 ,max(case when extract(day from schedule01::timestamp)=11 then state end) asday1124
25 ,max(case when extract(day from schedule01::timestamp)=12 then state end) asday1226
27 ,max(case when extract(day from schedule01::timestamp)=13 then state end) asday1328
29 fromtemp_schedule30
31 where extract(year from schedule01)=2017 and extract(month from schedule01)=6
32
33 group by schedule03;
View Code
3.将人员的值班状态通过汉字(0休 1班)显示出来，显示效果如下：
SQL语句(主要是实现case的嵌套)：
1 select schedule03 asname2
3 ,max(case when extract(day from schedule01::timestamp)=1 then (case when state='0' then '休' else '班' end) end) asday14
5 ,max(case when extract(day from schedule01::timestamp)=2 then (case when state='0' then '休' else '班' end) end) asday26
7 ,max(case when extract(day from schedule01::timestamp)=3 then (case when state='0' then '休' else '班' end) end) asday38
9 ,max(case when extract(day from schedule01::timestamp)=4 then (case when state='0' then '休' else '班' end) end) asday410
11 ,max(case when extract(day from schedule01::timestamp)=5 then (case when state='0' then '休' else '班' end) end) asday512
13 ,max(case when extract(day from schedule01::timestamp)=6 then (case when state='0' then '休' else '班' end) end) asday614
15 ,max(case when extract(day from schedule01::timestamp)=7 then (case when state='0' then '休' else '班' end) end) asday716
17 ,max(case when extract(day from schedule01::timestamp)=8 then (case when state='0' then '休' else '班' end) end) asday818
19 ,max(case when extract(day from schedule01::timestamp)=9 then (case when state='0' then '休' else '班' end) end) asday920
21 ,max(case when extract(day from schedule01::timestamp)=10 then (case when state='0' then '休' else '班' end) end) asday1022
23 ,max(case when extract(day from schedule01::timestamp)=11 then (case when state='0' then '休' else '班' end) end) asday1124
25 ,max(case when extract(day from schedule01::timestamp)=12 then (case when state='0' then '休' else '班' end) end) asday1226
27 ,max(case when extract(day from schedule01::timestamp)=13 then (case when state='0' then '休' else '班' end) end) asday1328
29 fromtemp_schedule30
31 where extract(year from schedule01)=2017 and extract(month from schedule01)=6
32
33 group by schedule03 ;
View Code
知识一点点的累积，技术一点点的提高！加油！
