<update id="updateCustomer" parameterType="com.entrym.domain.Customer"> UPDATE customer set <if test="name!=null">name=#{name,jdbcType=VARCHAR},</if> <if test="role!=null">role=#{role,jdbcType=VARCHAR},</if> <if test="userId != null">user_id = #{userId,jdbcType=INTEGER},</if> <if test="qq != null">qq = #{qq,jdbcType=VARCHAR},</if> <if test="mobile != null">mobile = #{mobile,jdbcType=VARCHAR}</if> WHERE id =#{id,jdbcType=BIGINT}
如果上面的mobile字段为null，执行下面的SQL语句
UPDATE customer set name=?,role=?,userId=?,qq=?， where id=?
where 前面有逗号“,”就会报错
使用trim可以删掉最后字段的逗号“,”
set已被包含在trim中，所以不用重复写了：
<update id="updateCustomer" parameterType="com.entrym.domain.Customer"> UPDATE customer <trim prefix="set" suffixOverrides=","> <if test="claimTime!=null">claim_time=#{claimTime,jdbcType=VARCHAR},</if> <if test="claimState!=null">claim_state=#{claimState,jdbcType=INTEGER},</if> <if test="name!=null">name=#{name,jdbcType=VARCHAR},</if> <if test="role!=null">role=#{role,jdbcType=VARCHAR},</if> <if test="platformAccount!=null">platform_account=#{platformAccount,jdbcType=VARCHAR},</if> <if test="collaborateTime!=null">collaborate_time=#{collaborateTime,jdbcType=VARCHAR},</if> <if test="collaborateState!=null">collaborate_state=#{collaborateState,jdbcType=INTEGER},</if> <if test="userId != null">user_id = #{userId,jdbcType=INTEGER},</if> <if test="qq != null">qq = #{qq,jdbcType=VARCHAR},</if> <if test="mobile != null">mobile = #{mobile,jdbcType=VARCHAR}</if> </trim> WHERE id =#{id,jdbcType=BIGINT} </update>
原文：http://www.cnblogs.com/Alwaysbecoding/p/6580674.html