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 GROUP BY Statement and SELECT Statement to group the same data.
GROUP BY is in a The basic syntax of the GROUP BY clause is given below: The GROUP BY clause must be placed in the In the GROUP BY clause, you can group one or more columns, but the grouped columns must exist in the list. Create the COMPANY table ( 下载 COMPANY SQL 文件 ), the data are as follows: The following example will be based on The following results are obtained: Now let’s add the following statement in the Now Now on the basis of The results are as follows: The following example uses the ORDER BY clause with the GROUP BY clause: The following results are obtained: SELECT Statement, put it in the WHRER After the clause and in front of the ORDER BY clause. 5.24.1. Grammar ¶
SELECT column-list FROM table_name WHERE [ conditions ] GROUP BY column1, column2....columnN ORDER BY column1, column2....columnN
WHERE After the condition in the clause, it must be placed before the ORDER BY clause. 5.24.2. Example ¶
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)
NAME Field values are grouped to find out each person’s total salary:runoobdb=# SELECT NAME, SUM(SALARY) FROM COMPANY GROUP BY NAME;
name | sum -------+------- Teddy | 20000 Paul | 20000 Mark | 65000 David | 85000 Allen | 15000 Kim | 45000 James | 10000 (7 rows)
CAMPANY Add three records to the table:INSERT INTO COMPANY VALUES (8, 'Paul', 24, 'Houston', 20000.00); INSERT INTO COMPANY VALUES (9, 'James', 44, 'Norway', 5000.00); INSERT INTO COMPANY VALUES (10, 'James', 45, 'Texas', 5000.00);
COMPANY There are duplicate names in the table, and the data is as follows: 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 8 | Paul | 24 | Houston | 20000 9 | James | 44 | Norway | 5000 10 | James | 45 | Texas | 5000 (10 rows)
NAME Field values are grouped to find out the total payroll of each customer:runoobdb=# SELECT NAME, SUM(SALARY) FROM COMPANY GROUP BY NAME ORDER BY NAME;
name | sum -------+------- Allen | 15000 David | 85000 James | 20000 Kim | 45000 Mark | 65000 Paul | 40000 Teddy | 20000 (7 rows)
runoobdb=# SELECT NAME, SUM(SALARY) FROM COMPANY GROUP BY NAME ORDER BY NAME DESC;
name | sum -------+------- Teddy | 20000 Paul | 40000 Mark | 65000 Kim | 45000 James | 20000 David | 85000 Allen | 15000 (7 rows)