对测试的表添加unique唯一约束。

alter table test.wc_res add unique

(word);​

1、insert IGNORE into test.wc_res(word,count)

values(#{word},#{count})

使用ignore into时，如果数据存在，不抛出错误，存在的数据不插入

2、insert  into test.wc_res(word,count)

values(#{word},#{count})

Caused by:

com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException:

Duplicate entry 'zhangfei' for key 'word'

​​​

3、​insert REPLACE

into test.wc_res(word,count) values(#{word},#{count})

1064 - You have an error in your SQL syntax; check the

manual that corresponds to your MySQL server version for the right

syntax to use near 'REPLACE  into

test.wc_res(word,count) values("zhangfei",2)' at line

1​

replace into时产生原因：语法错误。正确的语法应该是没有insert:

​REPLACE  into

test.wc_res(word,count) values(#{word},#{count})

如果存在primary or

unique相同的记录，则先删除掉。再插入新记录。​

4、insert … select … where not exist

根据select的条件判断是否插入，可以不光通过primary 和unique来判断，也可通过其它条件。例如：

INSERT INTO books (name) SELECT 'MySQL Manual' FROM dual WHERE

NOT EXISTS (SELECT id FROM books WHERE id = 1)