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;
时间和日期操作符：
“+”
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)
