本博客介绍一下Oracle merge合并函数，业务场景：新增数据的时候要先查询数据库是否已经有改数据，有数据就更新数据，没数据才新增数据，这是很常见的业务场景，如果是用Oracle数据库的话，其实直接用merge函数效率更快，而且merge函数性能也相对比较好

merge函数的语法：

MERGE INTO table_name alias1

USING (table|view|sub_query) alias2

ON (join condition)

WHEN MATCHED THEN

    UPDATE table_name

    SET col1 = col_val1,

           col2 = col_val2

WHEN NOT MATCHED THEN

    INSERT (column_list) VALUES (column_values);

举个例子：

SQL实现，意思是有数据就更新，没数据才新增

MERGE INTO t_config_related A1 USING(select '97547758-6f85-419e-85f9-b8f711ca2660' seq,

          '97547758-6f85-419e-85f9-b8f711ca2658' tipsSeq,

          to_number('1') appLevel,

          '24e1ccc38d9542189d1cc6c23f814a18' relaSeq from dual) A2

ON(A1.seq = A2.seq)

WHEN MATCHED THEN

UPDATE SET

        A1.tips_seq = A2.tipsSeq,

        A1.app_level = A2.appLevel,

        A1.rela_seq = A2.relaSeq

WHEN NOT MATCHED THEN

INSERT(seq , tips_seq , app_level , rela_seq)

VALUES(A2.seq , A2.tipsSeq , A2.appLevel , A2.relaSeq);

/**

   	 * 批量更新保存地区关联信息

   	 * @date   2019年2月21日上午11:17:10

   	 * @return

   	 */

   	@RequestMapping("/batchSaveTipsAreaConfig")

   	@ResponseBody

   	public ResultModel batchSaveTipsConfig(ApprTipsRelatedModel relatedModel) {

   		List<ApprTipsRelatedModel> areaTipsList = new ArrayList<ApprTipsRelatedModel>();

   		//封装批量更新的地区列表

   		String[] areaSeqs = StringUtils.split(relatedModel.getAreaSeq(),",");

   		for (String areaSeq : areaSeqs) {

   			ApprTipsRelatedModel areaRelatedModelNew = new ApprTipsRelatedModel();

   			areaRelatedModelNew.setSeq(commonService.generateUUID());

   			areaRelatedModelNew.setTipsSeq(relatedModel.getTipsSeq());

   			areaRelatedModelNew.setAppLevel(NumConstant.COMMON_NUM_TREE);

   			areaRelatedModelNew.setRelaSeq(areaSeq);

   		    areaTipsList.add(areaRelatedModelNew);

   	}

   		//批量更新新增数据

   		try {

   			this.tipsConfigService.batchSaveTipsRelatedConfig(areaTipsList);

   			return ResultModel.success("保存成功");

   		} catch(Exception e) {

   			logger.error("批量绑定地区异常:{}"+e);

  			throw new SuperControllerException();

   		}

   	}

注意要点：

在开发中我遇到一个异常，mybatis打印出来的SQL是这样的：

Preparing: MERGE INTO appr_tips_config_related A1 ? USING( ? ? ? ? ? select ? seq , ? tipsSeq , ? appLevel , ? relaSeq from dual ? ? ? ? ) A2 ? ON( ? ? ? ? ?A1.seq = A2.seq ? ? ?) ? WHEN MATCHED THEN ? ? UPDATE SET A1.seq = A2.seq, A1.tips_seq = A2.tipsSeq, A1.app_level = A2.appLevel, A1.rela_seq = A2.relaSeq ? ? ?WHEN NOT MATCHED THEN ? ? ?INSERT(seq,tip_seq,app_level,rela_seq) ? ? ? ? VALUES(A2.seq , A2.tipsSeq , A2.appLevel , A2.relaSeq)

可以看出什么问题？打印出的SQL有很多问号，那是因为SQL有空格导致的，所以使用merge函数不用随便加空格，不然会报错的

? USING( ? ? ? ? ? select ? seq , ? tipsSeq , ? appLevel , ? relaSeq from dual ? ? ? ? ) A2 ? ON( ? ? ? ? ?A1.seq = A2.seq ? ? ?) ?