postgreSQL常用函式

select coalesce( sum(duration) , 0)--若sum(duration)返回值為空，則為其賦值0

select to_date('2013-12-20','yyyy-mm-dd') --字串轉化為date型別
select (date '2013-10-28 01:00' - interval '50 minutes'|| ' ')--字串的拼接
select to_char( current_date, 'yyyy-mm-dd')--時間型別轉為為字串
select extract(hour from  timestamp '2013-10-28 01:00' - interval '1 days' ) --獲取一天前小時值
select extract(hour from current_time - interval '3 hours' ) --獲取三個小時前的小時
v_day_start := select to_char( current_date, 'yyyy-mm-dd')--賦值加型別轉換
select date_part('epoch', timestamp '2013-11-28 11:00'- timestamp '2013-11-28 01:30' );   --將時間差轉變為秒數
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' ); --把時間差轉化為秒
select 23+23 --數值計算
v_runtime := v_starttime_interval + v_runningtime + v_endtime_interval --儲存過程中的賦值加減操作
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';--時間型別的計算
select coalesce( sum(duration) , 0) from engine_test  where station = 'gcic_' || i_station  --根據傳入的引數i_station進行拼接字串拼接，然後作為查詢條件來使用
and createdon >=  '2013-12-12 10:30'
and createdon < '2013-12-12 12:30';

postgresql常用函式

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