mybatis中的is not null
时间: 2024-02-27 20:55:22 浏览: 35
在 MyBatis 中可以使用 `<if>` 标签来动态生成 SQL 语句,其中可以使用 `is not null` 条件来判断某个字段是否为 null。示例如下:
```xml
<select id="getUserList" resultType="User">
SELECT * FROM user
<where>
<if test="name != null">
and name = #{name}
</if>
<if test="age != null">
and age = #{age}
</if>
<if test="email != null">
and email is not null
</if>
</where>
</select>
```
在上面的示例中,当 `email` 不为 null 时,会生成 `and email is not null` 的 SQL 语句。
相关问题
mybatis isnull
MyBatis provides a built-in function called `isnull` that checks whether a value is null or not.
You can use this function in your MyBatis XML mapper files to conditionally execute a SQL statement based on whether a value is null or not.
Here's an example:
```xml
<select id="getUserById" resultType="User">
SELECT *
FROM users
WHERE id = #{id}
<if test="@org.apache.ibatis.jdbc.Null.null == username">
AND username IS NULL
</if>
<if test="@org.apache.ibatis.jdbc.NotNull@notNull(username)">
AND username = #{username}
</if>
</select>
```
In this example, the `isnull` function is used to check whether the `username` parameter is null or not. If it is null, the SQL statement will include a condition that checks whether the `username` column in the `users` table is null. If it is not null, the SQL statement will include a condition that checks whether the `username` column in the `users` table matches the `username` parameter.
Note that in order to use the `isnull` function, you need to include the `mybatis-3-jdbc-type-converter` dependency in your project.
QueryWrapper中的isnotnull在mybatis如何实现
在 MyBatis 中,可以使用 `<![CDATA[is not null]]>` 来实现 QueryWrapper 中的 `isNotNull` 方法。
例如,以下是一个示例查询:
```java
QueryWrapper<User> wrapper = new QueryWrapper<>();
wrapper.select("id", "name", "age")
.isNotNull("email")
.orderByDesc("id");
List<User> userList = userMapper.selectList(wrapper);
```
其中,`isNotNull("email")` 方法会生成以下 SQL 语句片段:
```sql
email is not null
```
注意,在使用 `isNotNull` 方法时,需要确保表中对应字段不为 NULL,否则查询结果可能会受到影响。