今天看工程時,遇到以下這種寫法html
<sql id="Base_Column_List" > APP_NAME, APP_STORE_ID, APP_IOS_ID, APP_IOS_VERSION, APP_IOS_UPD_FLAG, APP_ANDROID_VERSION, APP_ANDROID_UPD_FLAG, ANDROID_DOWNLOAD_URL, USER_PROTOCOL_URL, DATA_SERVER_URL, RESOURCE_SERVER_URL, WEBPAGE_SERVER_URL, SPLASH_IMG_URL, ABOUT_CONTENT, APP_IMG, UPD_USER_ID, UPD_TIME </sql> <select id="selectSysInfo" resultMap="BaseResultMap" > select <include refid="Base_Column_List" /> from t_sys_info limit 1 </select>
如上寫法和以下寫法結果同樣java
<select id="selectSysInfo" resultMap="BaseResultMap" > select APP_NAME, APP_STORE_ID, APP_IOS_ID, APP_IOS_VERSION, APP_IOS_UPD_FLAG, APP_ANDROID_VERSION, APP_ANDROID_UPD_FLAG, ANDROID_DOWNLOAD_URL, USER_PROTOCOL_URL, DATA_SERVER_URL, RESOURCE_SERVER_URL, WEBPAGE_SERVER_URL, SPLASH_IMG_URL, ABOUT_CONTENT, APP_IMG, UPD_USER_ID, UPD_TIME from t_sys_info limit 1 </select>
我一直採用的是以下寫法。sql
如上寫法的優點是 將公共返回部分提取出來,用在須要的不一樣查詢接口上。app
例子以下
code
<sql id="Base_Column_List" > APP_NAME, APP_STORE_ID, APP_IOS_ID, APP_IOS_VERSION, APP_IOS_UPD_FLAG, APP_ANDROID_VERSION, APP_ANDROID_UPD_FLAG, ANDROID_DOWNLOAD_URL, USER_PROTOCOL_URL, DATA_SERVER_URL, RESOURCE_SERVER_URL, WEBPAGE_SERVER_URL, SPLASH_IMG_URL, ABOUT_CONTENT, APP_IMG, UPD_USER_ID, UPD_TIME </sql> <!-- 查詢系統信息,返回系統信息表裏全部字段--> <select id="selectSysInfo" resultMap="BaseResultMap" > select <include refid="Base_Column_List" /> from t_sys_info limit 1 </select> <!-- 根據appName查詢系統信息,返回系統信息表裏全部字段--> <select id="selectByPrimaryKey" resultMap="BaseResultMap" parameterType="java.lang.String" > select <include refid="Base_Column_List" /> from t_sys_info where APP_NAME = #{appName,jdbcType=VARCHAR} </select>
如上兩種查詢都要返回系統信息表裏所有字段,若是不將公共部分(<sql>...</sql>之間的類容)提取出來,則查詢時須要寫兩次。
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