<if test="characteristicName != null and characteristicName !=''">
        AND CHARACTERISTIC_NAME=#{characteristicName}
    </if>

    <if test="characteristicName == null">
        AND CHARACTERISTIC_NAME is null
    </if>

需要注意的是

①  如果 characteristicName 欄位值為junk ,mybaties會把sql語句轉換成"select * from table where receivedName="junk

② 如果 characteristicName 欄位值為 "",則以上倆個條件都不能滿足,所以轉化後的sql語句是"select * from table where 1=1".