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。
In PostgreSQL TRUNCATE TABLE Used to delete the data of the table, but not the table structure.
It can also be used DROP TABLE Delete the table, but this command deletes the structure of the table, and if you want to insert data, you need to recreate the table.
Create The following example uses the The results are as follows: TRUNCATE TABLE Vs. DELETE It has the same effect, but because it doesn’t actually scan the table, it’s faster. In addition TRUNCATE TABLE Tablespaces can be freed immediately without the need for subsequent VACUUM Operation, which is very useful on large tables. The PostgreSQL VACUUM operation is used to free and reuse disk space occupied by update / delete rows. 5.36.1. Grammar ¶
TRUNCATE TABLE The basic syntax is as follows:TRUNCATE TABLE table_name;
5.36.2. Example ¶
COMPANY 表（ 下载 COMPANY SQL 文件 ), the data are as follows:runoobdb# select * from COMPANY; id | name | age | address | salary ----+-------+-----+-----------+-------- 1 | Paul | 32 | California| 20000 2 | Allen | 25 | Texas | 15000 3 | Teddy | 23 | Norway | 20000 4 | Mark | 25 | Rich-Mond | 65000 5 | David | 27 | Texas | 85000 6 | Kim | 22 | South-Hall| 45000 7 | James | 24 | Houston | 10000 (7 rows)
TRUNCATE TABLE To clean up COMPANY Table:runoobdb=# TRUNCATE TABLE COMPANY;
runoobdb=# SELECT * FROM CUSTOMERS; id | name | age | address | salary ----+------+-----+---------+-------- (0 rows)