解决MySQL报错Error querying database.Cause com.mysql.jdbc.exceptions.j
解决MySQL报错Error querying database. Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax.1.问题产生
项目测试环节，jdbc毗连过程where子句出现报错问题
org.apache.ibatis.exceptions.PersistenceException:
### Error querying database.Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: 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 'title = 'xxx'' at line 3
### The error may exist in com/lanyy/dao/BlogMapper.xml
### The error may involve com.lanyy.dao.BlogMapper.queryBlogIF-Inline
### The error occurred while setting parameters
### SQL: select * from blog where 1=1 title = ?
### Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: 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 'title = 'xxxx'' at line 3
https://i-blog.csdnimg.cn/blog_migrate/9a28bdb493294bfbb15024c2b54b119d.png
2.问题排查
where之后需接条件语句，需写where 1=1，假如引入标签则不要再写，标签会主动添加执行
https://i-blog.csdnimg.cn/blog_migrate/db31001d117be6ba454dce5f9b46d9e3.png
3.问题解决
引入<where>标签子句
where元素只会在至少有一个子元素的条件满足情况下才去插入 \ 查询，
这个“where”标签会知道假如它输入的信息中包含的标签有返回值（参数）的话，它就插入一个‘where’条件。
此外，假如标签返回的内容是以AND 或 OR 开头的，则它会剔除掉AND或OR。
<select id="queryBlogIF" parameterType="map" resultType="Blog">
select * from blog
<where>
<if test="title != null">
and title = #{title}
</if>
<if test="author != null">
and author = #{author}
</if>
</where>
</select>
不引入标签，只使用sql中where语句，需要在where后参加条件判定
<select id="queryBlogIF" parameterType="map" resultType="Blog">
<!-- 1=1恒等 条件永久成立 直接遍历blog表中所有信息 选择查询title或者author-->
select * from blog where 1=1
<if test="title != null">
and title = #{title}
</if>
<if test="author != null">
and author = #{author}
</if>
</select>
调试后运行乐成
https://i-blog.csdnimg.cn/blog_migrate/85ac420c2bc04dca1ed0e10190c9b494.png
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