PostgreSQL9.5.9学习篇布尔类型操作符select查询
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介绍：
布尔类型的操作符：逻辑操作符和比较操作符
逻辑操作符：and，or，not
需要注意的是：false and null结果为false
比较运算符：is
is true
is false
is not true
is not false
is unknown
is not unknown
is null
is not null
登陆测试数据库创建测试测试表插入数据来演示：
1.登陆库testdb1:
[[email protected] ~]$ psql -Utestwjw -h 127.0.0.1 -d testdb1 -p 36985
Password for user testwjw: 输入密码：558996
psql.bin (9.5.9)
Type "help" for help.
2.创建表：
boolean的状态要么是true要么是false，如果是unknown，用NULL表示。
boolean在SQL中可以用不带引号的TRUE和FALSE表示，也可以用更多的表示真假的带引号的字符表示，如‘true‘,‘false‘,‘yes‘,‘no‘,‘1‘,‘0‘等
testdb1=> create table t (id int, nan boolean, note text);
CREATE TABLE
3.查看库中所有的表：
testdb1=> \dt
List of relations
Schema | Name | Type | Owner
--------+-------+-------+---------
public | t | table | testwjw
public | tlb01 | table | testwjw
testdb1=>
4.t表中插入数据：
testdb1=> insert into t values(1,TRUE,‘TRUE‘);
INSERT 0 1
testdb1=> insert into t values(2,FALSE,‘FALSE‘);
INSERT 0 1
testdb1=> insert into t values(3,tRue,‘tRue‘)
testdb1-> ;
INSERT 0 1
testdb1=> insert into t values(4,fAlse,‘fAlse‘);
INSERT 0 1
给t表中插入空数值NULL:
testdb1=> insert into t values(11,null,‘null‘);
INSERT 0 1
testdb1=> insert into t values(11,NULL,‘NULL‘);
INSERT 0 1
5.查看表中的数值：
testdb1=> select * from t;
id | nan | note
----+-----+-------
1 | t | TRUE
2 | f | FALSE
3 | t | tRue
4 | f | fAlse
11 | | null
11 | | NULL
(6 rows)
select * from t where nan=‘t‘;
id | nan | note
----+-----+------
1 | t | TRUE
3 | t | tRue
(2 rows)
testdb1=> select * from t where nan; 特殊的查询方式：
id | nan | note
----+-----+------
1 | t | TRUE
3 | t | tRue
(2 rows)
testdb1=>
testdb1=> select * from t where nan<>‘t‘;
id | nan | note
----+-----+-------
2 | f | FALSE
4 | f | fAlse
(2 rows)
testdb1=>
testdb1=> select * from t where not nan;
id | nan | note
----+-----+-------
2 | f | FALSE
4 | f | fAlse
(2 rows)
testdb1=>
testdb1=> select * from t where nan or not nan;
id | nan | note
----+-----+-------
1 | t | TRUE
2 | f | FALSE
3 | t | tRue
4 | f | fAlse
(4 rows)
testdb1=> select * from t where nan and not nan;
id | nan | note
----+-----+------
(0 rows)
testdb1=> select * from t where nan is null;
id | nan | note
----+-----+------
11 | | null
11 | | NULL
(2 rows)
testdb1=> select * from t where nan is unknown; ####神奇
id | nan | note
----+-----+------
11 | | null
11 | | NULL
(2 rows)
testdb1=>
testdb1=> select * from t where nan is not null;
id | nan | note
----+-----+-------
1 | t | TRUE
2 | f | FALSE
3 | t | tRue
4 | f | fAlse
(4 rows)
testdb1=>
插入数值：
testdb1=> insert into t values(7,‘t‘,‘‘‘t‘‘‘);
INSERT 0 1
testdb1=> insert into t values(8,‘f‘,‘‘‘f‘‘‘);
INSERT 0 1
testdb1=> insert into t values(9,‘yes‘,‘‘‘yes‘‘‘);
INSERT 0 1
testdb1=> insert into t values(10,‘0‘,‘‘‘0‘‘‘);
INSERT 0 1
testdb1=> select * from t;
id | nan | note
----+-----+-------
1 | t | TRUE
2 | f | FALSE
3 | t | tRue
4 | f | fAlse
11 | | null
11 | | NULL
7 | t | ‘t‘
8 | f | ‘f‘
9 | t | ‘yes‘
10 | f | ‘0‘
(10 rows)
testdb1=> select * from t where nan is not true ;
id | nan | note
----+-----+-------
2 | f | FALSE
4 | f | fAlse
11 | | null
11 | | NULL
8 | f | ‘f‘
10 | f | ‘0‘
(6 rows)
testdb1=> select * from t where nan is true ;
id | nan | note
----+-----+-------
1 | t | TRUE
3 | t | tRue
7 | t | ‘t‘
9 | t | ‘yes‘
(4 rows)
testdb1=> select * from t where nan is not false ;
id | nan | note
----+-----+-------
1 | t | TRUE
3 | t | tRue
11 | | null
11 | | NULL
7 | t | ‘t‘
9 | t | ‘yes‘
(6 rows)
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