最近几年来，地理信息系统无论是在理论上还是应用上都处在一个飞速发展的阶段。 GIS被应用于多个领域的建模和决策支持，如城市管理、区划、环境整治等等，地理信息成为信息时代重要的组成部分之一； “数字地球”概念的提出，更进一步推动了作为其技术支撑的GIS的发展。 与此同时，一些学者致力于相关的理论研究，如空间感知、空间数据误差、空间关系的形式化等等。 这恰好说明了地理信息系统作为应用技术和学科的两个方面，并且这两个方面构成了相互促进的发展过程。
5.43.1. Date / time operator ¶
The following table shows the behavior of basic arithmetic operators (+, * , etc.):
Operator | Examples | Result |
|---|---|---|
| Date ‘2001-09-28’ + integer’ 7’ | Date ‘2001-10-05’ |
| Date ‘2001-09-28’ + interval’1 hour’ | Timestamp ‘2001-09-28 01GRV 0000’ |
| Date ‘2001-09-28’ + time’ 03purl 00’ | Timestamp ‘2001-09-28 03GRV 0000’ |
| Interval’1 day’ + interval’1 hour’ | Interval’1 day 01purl 0000’ |
| Timestamp ‘2001-09-28 01 hours’ hours’ + interval’ 23 | Timestamp ‘2001-09-29 0000Rule 0000’ |
| Time ‘01VOUR 00’ + interval’ 3 hours’ | Time ‘04VOUR 00UR 00’ |
|
| Interval’- 23PUR 0000’ |
| Date ‘2001-10-01’-date ‘2001-09-28’ | Integer’3’ (days) |
| Date ‘2001-10-01’-integer’7’ | Date ‘2001-09-24’ |
| Date ‘2001-09-28’-interval’1 hour’ | Timestamp ‘2001-09-27 2300RV 00’ |
| Time ‘05VR 00’-time’ 03VR 00’ | Interval ‘02VOUR 00UR 00’ |
| Time ‘05VOV 00’-interval’ 2 hours’ | Time ‘03VOULAR 0000’ |
| Timestamp ‘2001-09-28 2314 00’-interval’ 23 hours’ | Timestamp ‘2001-09-28 0000RV 0000’ |
| Interval’1 day’-interval’1 hour’ | Interval’1 day-01PUR 0000’ |
| Timestamp ‘2001-09-29 03VR 00’-timestamp’ 2001-09-27 12VR 00’ | Interval’1 day 15lv 0000’ |
| 900 * interval’1 second’ | Interval ‘00Rose 1500’ |
| 21 * interval’1 day’ | Interval’21 days’ |
| Double precision ‘3.5’ * interval’1 hour’ | Interval ‘03PUR 30PUR 00’ |
| Interval’1 hour’ / double precision ‘1.5’ | Interval ‘00Rose 40Rose 00’ |
5.43.2. Date / time function ¶
Function | Return type | Description | Examples | Result |
|---|---|---|---|---|
Age (timestamp, timestamp) | Interval | The result of “symbolization” after subtracting parameters, use year and month, not just days | Age (timestamp ‘2001-04-10, timestamp’ 1957-06-13’) | 43 years 9 mons 27 days |
Age (timestamp) | Interval | 从current_date减去参数后的结果（在午夜） | Age (timestamp ‘1957-06-13’) | 43 years 8 mons 3 days |
Clock_timestamp () | Timestamp with time zone | The current timestamp of the real-time clock (changes when the statement is executed) | ||
current_date | Date | Current date | ||
current_time | Time with time zone | Time of the day | ||
current_timestamp | Timestamp with time zone | Timestamp at the start of the current transaction | ||
Date_part (text, timestamp) | Double precision | Get subdomain (equivalent to extract) | Date_part (‘hour’, timestamp’ 2001-02-16 20 38 40’) | 20 |
Date_part (text, interval) | Double precision | Get subdomain (equivalent to extract) | Date_part (‘month’, interval’ 2 years 3 months’) | 3 |
Date_trunc (text, timestamp) | Timestamp | Truncated to a specified precision | Date_trunc (‘hour’, timestamp’ 2001-02-16 20 38 40’) | 2001-2-16 20:00 |
Date_trunc (text, interval) | Interval | Intercept the specified precision | Date_trunc (‘hour’, interval’ 2 days 3 hours 40 minutes’) | 2 days 03:00:00 |
Extract (field from timestamp) | Double precision | Get subdomain | Extract (hour from timestamp ‘2001-02-16 20-38-40’) | 20 |
Extract (field from interval) | Double precision | Get subdomain | Extract (month from interval’2 years 3 months’) | 3 |
Isfinite (date) | Boolean | Test whether it is a finite date (not + /-infinite) | Isfinite (date ‘2001-02-16’) | TRUE |
Isfinite (timestamp) | Boolean | Test whether it is a finite timestamp (not + /-infinite) | Isfinite (timestamp ‘2001-02-16 21) | TRUE |
Isfinite (interval) | Boolean | Test whether there is a finite time interval | Isfinite (interval’4 hours’) | TRUE |
Justify_days (interval) | Interval | Adjust the time interval according to 30 days per month | Justify_days (interval’35 days’) | 1 mon 5 days |
Justify_hours (interval) | Interval | Adjust the interval according to 24 hours a day | Justify_hours (interval’27 hours’) | 1 day 03:00:00 |
Justify_interval (interval) | Interval | 使用justify_days和justify_hours调整时间间隔的同时进行正负号调整 | Justify_interval (interval’1 mon-1 hour’) | 29 days 23:00:00 |
Localtime | Time | Time of the day | ||
Localtimestamp | Timestamp | Timestamp at the start of the current transaction | ||
Make_date (year int, month int, day int) | Date | Create a date for the year, month, and day fields | Make_date (2013, 7, 15) | 2013-7-15 |
Make_interval (years int DEFAULT 0, months int DEFAULT 0, weeks int DEFAULT 0, days int DEFAULT 0, hours int DEFAULT 0, mins int DEFAULT 0, secs double precision DEFAULT 0) | Interval | Create intervals from the year, month, week, day, hour, minute, and second fields | Make_interval (days: = 10) | 10 days |
Make_time (hour int, min int, sec double precision) | Time | Create a time from the hour, minute, and second fields | Make_time (8,15,23.5) | 15:23.5 |
Make_timestamp (year int, month int, day int, hour int, min int, sec double precision) | Timestamp | Create a timestamp from the year, month, day, hour, minute, and second fields | Make_timestamp (2013, 7, 15, 8, 15, 23.5) | 15:23.5 |
Make_timestamptz (year int, month int, day int, hour int, min int, sec double precision [ timezone text ] ) | Timestamp with time zone | Create a timestamp with a time zone from the year, month, day, hour, minute, and second fields. The current time zone is used when no timezone is specified. | Make_timestamptz (2013, 7, 15, 8, 15, 23.5) | 2013-07-15 0815 purge 15 purl 23.5mm 01 |
Now () | Timestamp with time zone | Timestamp at the start of the current transaction | ||
Statement_timestamp () | Timestamp with time zone | Current timestamp of the real-time clock | ||
Timeofday () | Text | 与clock_timestamp相同，但结果是一个text 字符串； | ||
Transaction_timestamp () | Timestamp with time zone | Timestamp at the start of the current transaction |