delete 删除语句

delete 用于删除数据，核心是掌握条件控制与软删除实现。

基础删除

<delete id="deleteById">
    DELETE FROM user WHERE id = #{id}
</delete>

int rows = mapper.deleteById(id);
// rows 为影响行数，0 表示未删除任何数据

条件删除

<delete id="deleteByEmail">
    DELETE FROM user WHERE email = #{email}
</delete>

<delete id="deleteBatch">
    DELETE FROM user WHERE id IN
    <foreach collection="ids" item="id" open="(" separator="," close=")">
        #{id}
    </foreach>
</delete>

软删除

方式一：更新状态字段

<update id="softDeleteById">
    UPDATE user SET status = 0, update_time = #{updateTime}
    WHERE id = #{id}
</update>

方式二：使用逻辑删除字段

<select id="selectActive" resultMap="BaseResultMap">
    SELECT * FROM user WHERE is_deleted = 0
</select>

注意：软删除推荐在查询时自动过滤已删除数据，避免物理删除后数据丢失。

级联删除

<delete id="deleteUserAndOrders">
    DELETE u, o FROM user u
    LEFT JOIN orders o ON u.id = o.user_id
    WHERE u.id = #{id}
</delete>

注意：级联删除需谨慎使用，推荐通过外键约束或业务层控制删除顺序。

要点总结

• delete 返回影响行数，0 表示未删除任何数据
• 批量删除使用 foreach 标签构造 IN 条件
• 软删除通过更新状态字段或逻辑删除字段实现
• 级联删除需控制删除顺序，避免数据不一致