在PostgreSQL中可以直接对timestamp进行加减运算：

01.SELECT now()::timestamp + '1 year';  
02.SELECT now()::timestamp + '1 month';  
03.SELECT now()::timestamp + '1 day';  
04.SELECT now()::timestamp + '1 hour';  
05.SELECT now()::timestamp + '1 min';  
06.SELECT now()::timestamp + '1 sec';  
07.select now()::timestamp + '1 year 1 month 1 day 1 hour 1 min 1 sec';  
08.SELECT now()::timestamp + (col || ' day')::interval FROM table

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