时间/日期函数和操作符

时间日期操作符

用户在使用时间和日期操作符时，对应的操作数请使用明确的类型前缀修饰，以确保数据库在解析操作数的时候能够与用户预期一致，不会产生用户非预期的结果。比如下面示例没有明确数据类型就会出现异常错误。

SELECT date '2001-10-01' - '7' AS RESULT;

表 1 时间和日期操作符

操作符

示例

openGauss=# SELECT date '2001-9-28' + integer '7' AS RESULT;

   result
\------------
 2001-10-05 00:00:00
(1 row)

openGauss=# SELECT date '2001-09-28' + interval '1 hour' AS RESULT;
       result        
\---------------------
 2001-09-28 01:00:00
(1 row)

openGauss=# SELECT date '2001-09-28' + time '03:00' AS RESULT;
       result        
\--------------------
 2001-09-28 03:00:00
(1 row)

openGauss=# SELECT interval '1 day' + interval '1 hour' AS RESULT;
     result     
\----------------
 1 day 01:00:00
(1 row)

openGauss=# SELECT timestamp '2001-09-28 01:00' + interval '23 hours' AS RESULT;
       result        
\---------------------
 2001-09-29 00:00:00
(1 row)

openGauss=# SELECT time '01:00' + interval '3 hours' AS RESULT;
  result  
\----------
 04:00:00
(1 row)

openGauss=# SELECT date '2001-10-01' - date '2001-09-28' AS RESULT;
 result
\--------
 3 days
(1 row)

openGauss=# SELECT date '2001-10-01' - integer '7' AS RESULT;
       result        
\---------------------
 2001-09-24 00:00:00
(1 row)

openGauss=# SELECT date '2001-09-28' - interval '1 hour' AS RESULT;
       result        
\---------------------
 2001-09-27 23:00:00
(1 row)

openGauss=# SELECT time '05:00' - time '03:00' AS RESULT;
  result  
\----------
 02:00:00
(1 row)

openGauss=# SELECT time '05:00' - interval '2 hours' AS RESULT;
  result  
\----------
 03:00:00
(1 row)

openGauss=# SELECT timestamp '2001-09-28 23:00' - interval '23 hours' AS RESULT;
       result        
\---------------------
 2001-09-28 00:00:00
(1 row)

openGauss=# SELECT interval '1 day' - interval '1 hour' AS RESULT;
  result  
\----------
 23:00:00
(1 row)

openGauss=# SELECT timestamp '2001-09-29 03:00' - timestamp '2001-09-27 12:00' AS RESULT;
     result     
\----------------
 1 day 15:00:00
(1 row)

openGauss=# SELECT 900 * interval '1 second' AS RESULT;
  result  
\----------
 00:15:00
(1 row)

openGauss=# SELECT 21 * interval '1 day' AS RESULT;
 result  
\---------
 21 days
(1 row)

openGauss=# SELECT double precision '3.5' * interval '1 hour' AS RESULT;
  result  
\----------
 03:30:00
(1 row)

openGauss=# SELECT interval '1 hour' / double precision '1.5' AS RESULT;
  result  
\----------
 00:40:00
(1 row)

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时间/日期函数和操作符

时间日期操作符