postgreSQL常用函数

select coalesce( sum(duration),0)--若sum(duration)返回值为空，则为其赋值0

select to_date('2013-12-20','YYYY-MM-DD') --字符串转化为date类型

select (date '2013-10-28 01:00' - interval '50 minutes'|| ' ')--字符串的拼接

select to_char( CURRENT_DATE,'YYYY-MM-DD')--时间类型转为为字符串

SELECT EXTRACT(HOUR FROM  timestamp '2013-10-28 01:00' - interval '1 days' ) --获取一天前小时值

SELECT EXTRACT(HOUR FROM CURRENT_TIME - interval '3 hours' ) --获取三个小时前的小时

v_day_start := select to_char( CURRENT_Date,'YYYY-MM-DD')--赋值加类型转换

select date_part('epoch',timestamp '2013-11-28 11:00'- timestamp '2013-11-28 01:30' );   --将时间差转变为秒数

select sum(duration) from engine_test where  state_start >='2013-12-12 12:30' and state_stop <'2013-12-12 14:30' and station='GCIC_TC01'
select date_part('epoch',timestamp '2013-11-28 01:00'- timestamp '2013-11-27 17:30' ); --把时间差转化为秒
select 23+23 --数值计算
v_runtime := v_starttime_interval + v_runningtime + v_endtime_interval --存储过程中的赋值加减操作

select state_stop - '2013-12-12 12:30' from engine_test 
where state_start <= '2013-12-12 12:30' and state_stop > '2013-12-12 12:30'
and type = 1 and station='GCIC_' || 'TC02';--时间类型的计算


select coalesce( sum(duration),0) from engine_test  where station = 'GCIC_' || i_station  --根据传入的参数i_station进行拼接字符串拼接，然后作为查询条件来使用
     and createdon >=  '2013-12-12 10:30'
     and createdon < '2013-12-12 12:30';

（编辑：李大同）

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