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第 5 章 DML

目录

5.1. INSERT
5.1.1. 自动截取字符串
5.1.2. INSERT IGNORE INTO
5.2. copy
5.2.1. wget

5.1. INSERT

5.1.1. 自动截取字符串

CREATE TABLE test (c varchar(5));
			

现在开始插入数据库,每次增加一个长度

			
test=> INSERT INTO test VALUES ('1');
INSERT 0 1
test=> INSERT INTO test VALUES ('12');
INSERT 0 1
test=> INSERT INTO test VALUES ('123');
INSERT 0 1
test=> INSERT INTO test VALUES ('1234');
INSERT 0 1
test=> INSERT INTO test VALUES ('12345');
INSERT 0 1
test=> INSERT INTO test VALUES ('123456');
ERROR:  value too long for type character varying(5)
test=> INSERT INTO test VALUES ('1234567');
ERROR:  value too long for type character varying(5)
test=>
			
			

超出长度会提示 ERROR: value too long for type character varying(5)

通过 ::varchar(5) 截取5前五个字符,后面抛弃

			
test=> INSERT INTO test VALUES ('123456'::varchar(5));
INSERT 0 1
test=> INSERT INTO test VALUES ('1234567'::varchar(5));
INSERT 0 1
test=> INSERT INTO test VALUES ('12345678'::varchar(5));
INSERT 0 1
			
			

超过的部分被自动截取

			
test=> select * from test;
   c
-------
 1
 12
 123
 1234
 12345
 12345
 12345
 12345
(8 rows)
			
			

5.1.2. INSERT IGNORE INTO

PostgreSQL 没有 MySQL INSERT IGNORE INTO 用法,可以使用下面方法替代

insert into profile(wechat,username,name) select wechat,username,name from member where description like '%5%' and NOT EXISTS (select 1 from profile where profile.wechat = member.wechat);			
			
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