Mybatis动态ＳＱＬ

Posted 2020-06-13

１．动态SQL基本标签

•if

•choose (when, otherwise)

•trim (where, set)

•foreach

２．IF 具体用法

<select id="XX"
 resultType="Blog">
 SELECT * FROM BLOG
 WHERE state = ‘ACTIVE’
 <if test="title != null">
 AND title like #{title}
 </if>
</select>

　　多个IF注意第二个ｉｆ语句里的表达式

<select id="XX"
 resultType="Blog">
 SELECT * FROM BLOG WHERE state = ‘ACTIVE’
 <if test="title != null">
 AND title like #{title}
 </if>
 <if test="author != null and author.name != null">
 AND author_name like #{author.name}
 </if>
</select>

　　３．类似　if ,else用法例子

<select id="XX"
 resultType="Blog">
 SELECT * FROM BLOG WHERE state = ‘ACTIVE’
 <choose>
 <when test="title != null">
 AND title like #{title}
 </when>
 <when test="author != null and author.name != null">
 AND author_name like #{author.name}
 </when>
 <otherwise>
 AND featured = 1
 </otherwise>
 </choose>

　　4．Where用法例子

<select id="XX"
 resultType="Blog">
 SELECT * FROM BLOG
 WHERE
 <if test="state != null">
 state = #{state}
 </if>
 <if test="title != null">
 AND title like #{title}
 </if>
 <if test="author != null and author.name != null">
 AND author_name like #{author.name}
 </if>
</select>

　　

<select id="XX"
 resultType="Blog">
 SELECT * FROM BLOG
 <where>
 <if test="state != null">
 state = #{state}
 </if>
 <if test="title != null">
 AND title like #{title}
 </if>
 <if test="author != null and author.name != null">
 AND author_name like #{author.name}
 </if>
 </where>
</select>

6．trim用法

<trim prefix="WHERE" prefixOverrides="AND |OR ">
 ...
</trim>

　　７．set用法注意set是sql语句中update table set.....不是将一个参数set到一个属性中

<update id="updateAuthorIfNecessary">
 update Author
 <set>
 <if test="username != null">username=#{username},</if>
 <if test="password != null">password=#{password},</if>
 <if test="email != null">email=#{email},</if>
 <if test="bio != null">bio=#{bio}</if>
 </set>
 where id=#{id}
</update>

8.foreach用法

<select id="selectPostIn" resultType="domain.blog.Post">
 SELECT *
 FROM POST P
 WHERE ID in
 <foreach item="item" index="index" collection="list"
 open="(" separator="," close=")">
 #{item}
 </foreach>
</select>