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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 测试: test=# create table t (ID int,nan boolean,note text); CREATE table test=# insert into t values(1,TRUE,'TRUE'); INSERT 0 1 test=# insert into t values(2,falSE,'falSE'); INSERT 0 1 test=# insert into t values(3,tRue,'tRue'); INSERT 0 1 test=# insert into t values(4,false,'false'); INSERT 0 1 test=# insert into t values(5,'tRuE','tRuE'); test=# delete from t where ID=5; deletE 1 test=# insert into t values(5,'''tRuE'''); INSERT 0 1 test=# insert into t values(6,'falsE','''falsE'''); INSERT 0 1 test=# insert into t values(7,'t','''t'''); INSERT 0 1 test=# insert into t values(8,'f','''f'''); INSERT 0 1 test=# insert into t values(9,'''yes'''); INSERT 0 1 test=# insert into t values(10,'0','''0'''); INSERT 0 1 test=# SELEct * FROM t; ID | nan | note ----+-----+--------- 1 | t | TRUE 2 | f | falSE 3 | t | tRue 4 | f | false 5 | t | 'tRuE' 6 | f | 'falsE' 7 | t | 't' 8 | f | 'f' 9 | t | 'yes' 10 | f | '0' (10 rows) test=# insert into t values(11,'',''''''); ---与Oracle不同,oracle没有Boolean数据类型。。。 ERROR: invalID input Syntax for type Boolean: "" liNE 1: insert into t values(11,''''''); ^ test=# insert into t values(11,null,'null'); INSERT 0 1 test=# SELEct * FROM t; ID | nan | note ----+-----+--------- 1 | t | TRUE 2 | f | falSE 3 | t | tRue 4 | f | false 5 | t | 'tRuE' 6 | f | 'falsE' 7 | t | 't' 8 | f | 'f' 9 | t | 'yes' 10 | f | '0' 11 | | null (11 rows) test=# insert into t values(11,NulL,'NulL'); INSERT 0 1 test=# SELEct * FROM t; ID | nan | note ----+-----+--------- 1 | t | TRUE 2 | f | falSE 3 | t | tRue 4 | f | false 5 | t | 'tRuE' 6 | f | 'falsE' 7 | t | 't' 8 | f | 'f' 9 | t | 'yes' 10 | f | '0' 11 | | null ---注意null在表中存的为空值,并非null这个单词,因为,如果这个单词本身是4个字母的单词。 11 | | NulL (12 rows) test=# SELEct * FROM t where nan='t'; ID | nan | note ----+-----+-------- 1 | t | TRUE 3 | t | tRue 5 | t | 'tRuE' 7 | t | 't' 9 | t | 'yes' (5 rows) test=# SELEct * FROM t where nan; --挺神奇的查询方式 ID | nan | note ----+-----+-------- 1 | t | TRUE 3 | t | tRue 5 | t | 'tRuE' 7 | t | 't' 9 | t | 'yes' (5 rows) test=# SELEct * FROM t where nan<>'t'; ID | nan | note ----+-----+--------- 2 | f | falSE 4 | f | false 6 | f | 'falsE' 8 | f | 'f' 10 | f | '0' (5 rows) test=# SELEct * FROM t where not nan; ID | nan | note ----+-----+--------- 2 | f | falSE 4 | f | false 6 | f | 'falsE' 8 | f | 'f' 10 | f | '0' (5 rows) test=# SELEct * FROM t where nan is null; ID | nan | note ----+-----+------ 11 | | null 11 | | NulL (2 rows) test=# SELEct * FROM t where nan is unkNown; ---神奇 ID | nan | note ----+-----+------ 11 | | null 11 | | NulL (2 rows) test=# SELEct * FROM t where nan is not null; ID | nan | note ----+-----+--------- 1 | t | TRUE 2 | f | falSE 3 | t | tRue 4 | f | false 5 | t | 'tRuE' 6 | f | 'falsE' 7 | t | 't' 8 | f | 'f' 9 | t | 'yes' 10 | f | '0' (10 rows) 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
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