考虑一下表 COMPANY 有以下记录:
testdb=# 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 | yiibai.com | 24 | Houston2 | 10000 (7 rows)
下面是简单的例子,显示使用PostgreSQL比较操作符:
在这里,我们已经使用WHERE子句将在一个单独的章节解释,但现在可以明白,WHERE子句用于把一个条件语句与SELECT语句一起。
下面的SELECT语句列表的工资大于50,000.00下来的所有记录:
testdb=# SELECT * FROM COMPANY WHERE SALARY > 50000;
以上PostgreSQL的表会产生以下结果:
id | name | age |address | salary ----+-------+-----+-----------+-------- 4 | Mark | 25 | Rich-Mond | 65000 5 | David | 27 | Texas | 85000 (2 rows)
下面的SELECT语句了所有的记录,工资等于20,000.00列表:
testdb=# SELECT * FROM COMPANY WHERE SALARY = 20000;
以上PostgreSQL的表会产生以下结果:
id | name | age | address | salary ----+-------+-----+-------------+-------- 1 | Paul | 32 | California | 20000 3 | Teddy | 23 | Norway | 20000 (2 rows)
下面的SELECT语句了所有的记录,工资不等于20,000.00列表:
testdb=# SELECT * FROM COMPANY WHERE SALARY != 20000;
以上PostgreSQL表会产生以下结果:
id | name | age | address | salary ----+-------+-----+-------------+-------- 2 | Allen | 25 | Texas | 15000 4 | Mark | 25 | Rich-Mond | 65000 5 | David | 27 | Texas | 85000 6 | Kim | 22 | South-Hall | 45000 7 | James | 24 | Houston | 10000 (5 rows)
下面的SELECT语句了所有的记录,工资不等于20,000.00列表:
testdb=# SELECT * FROM COMPANY WHERE SALARY <> 20000;
以上PostgreSQL的表会产生以下结果:
id | name | age | address | salary ----+-------+-----+------------+-------- 2 | Allen | 25 | Texas | 15000 4 | Mark | 25 | Rich-Mond | 65000 5 | David | 27 | Texas | 85000 6 | Kim | 22 | South-Hall | 45000 7 | James | 24 | Houston | 10000 (5 rows)
下面的SELECT语句列表的工资大于或等于65,000.00下来的所有记录:
testdb=# SELECT * FROM COMPANY WHERE SALARY >= 65000;
以上PostgreSQL表会产生以下结果:
id | name | age | address | salary ----+-------+-----+-----------+-------- 4 | Mark | 25 | Rich-Mond | 65000 5 | David | 27 | Texas | 85000 (2 rows)