Oracle數據庫： select * from (select t1.name,t2.name from student t1, class t2 where t1.id=t2.id) F where 1=1;
MongoDB: 什么鬼？
非關系型數據庫多表聯查讓人崩潰
@Autowired private MongoTemplate mongoTemplate; @RequestMapping(value = "/queryByMap.html", method = RequestMethod.GET) public Map<String, Object> queryByMap() { //定義分組字段 String[] groupIds = new String[] {"$_id","$name","$msg","$itemList", "$instanceItem.elementName", "$instanceItem"}; //定義查詢條件 Criteria criteria = new Criteria(); //相當於where username = "zhangsan" criteria.and("name").is("name0"); //相當於 where age not in("15","20") //criteria.and("age").nin("15","20"); criteria.and("msg").is("message0"); //in操作對應的語句 //criteria.and("").in(); //定義排序條件 List<Sort.Order> orders = new ArrayList(); orders.add(new Sort.Order(Sort.Direction.DESC, "name")); Sort sort = Sort.by(orders); //聯合查詢條件 Aggregation newAggregation = Aggregation.newAggregation( Aggregation.lookup("UDT_TestInstanceItem","name","elementName","instanceItem"), //從表名，主表聯接字段，從表聯接字段，別名 Aggregation.unwind("$itemList"), Aggregation.match(criteria), Aggregation.group(groupIds) .last("$name").as("名稱")//取值，起別名 .first("$instanceItem.elementName").as("父項名稱") .first("$instanceItem.msg").as("子項msg") .first("$instanceItem.name").as("子項名稱"), Aggregation.sort(sort), Aggregation.skip(0),//Long類型的參數 Aggregation.limit(100) ); //查詢 AggregationResults<BasicDBObject> aggregate = mongoTemplate.aggregate( newAggregation ,"UDT_TestInstance",BasicDBObject.class //A表，是查詢的主表 ); int count = mongoTemplate.aggregate(newAggregation ,"UDT_TestInstance",BasicDBObject.class).getMappedResults().size(); Map<String, Object> result = new HashMap<>(); result.put("result", aggregate.getMappedResults()); result.put("count", count); return result; }
上面的多表聯查方法看起來有點繁瑣，而且我在生產環境中運用的時候總是查不出數數據(demo可以查出數據)，所以用了下面的方法：
1 LookupOperation lookupOperation=LookupOperation.newLookup(). 2 from("DYNC_EXT_TestInstanceItem"). //關聯從表名 3 localField("partVersion"). //主表關聯字段 4 foreignField("partVersion").//從表關聯的字段 5 as("result"); //查詢結果名 6 AggregationOperation match = Aggregation.match(criteria); 7 Aggregation aggregation=Aggregation.newAggregation(match, lookupOperation); //多條件 8 List<Map> results = mongoTemplate.aggregate(aggregation,"DYNC_EXT_TestInstance", Map.class).getMappedResults(); 9 //上面的DYNC_EXT_TestInstance必須是查詢的主表名 10 System.out.println(JSON.toJSONString(results));
這種寫法閱讀起來簡單，有效適合小白
還有一種方法是利用Java中的集合，分別查出多張表的數據存在List集合中，在通過循環比較得出符合的數據。