Question

我是sql的新手，正在尝试将来自三个不同表的列值组合在一起，并在DB2 Warehouse on Cloud中合并为一行。每个表只包含一行和唯一列名。所以我想要的只是将这三个到一行加入原始列名。

每个表都是根据如下语句构建的：

SELECT SUM(FUEL_TEMP.FUEL_MLAD_VALUE) AS FUEL 
FROM
    (SELECT ML_ANOMALY_DETECTION.MLAD_METRIC AS MLAD_METRIC, ML_ANOMALY_DETECTION.MLAD_VALUE AS FUEL_MLAD_VALUE, ML_ANOMALY_DETECTION.TAG_NAME AS TAG_NAME, ML_ANOMALY_DETECTION.DATETIME AS DATETIME, DATA_CONFIG.SYSTEM_NAME AS SYSTEM_NAME
     FROM ML_ANOMALY_DETECTION 
         INNER JOIN DATA_CONFIG ON 
               (ML_ANOMALY_DETECTION.TAG_NAME  =DATA_CONFIG.TAG_NAME AND 
                DATA_CONFIG.SYSTEM_NAME = 'FUEL') 
     WHERE ML_ANOMALY_DETECTION.MLAD_METRIC = 'IFOREST_SCORE'
       AND ML_ANOMALY_DETECTION.DATETIME >= (CURRENT DATE - 9 DAYS) 
     ORDER BY DATETIME DESC)
AS FUEL_TEMP

我已尝试过JOIN，INNER JOIN，UNION / UNION ALL，但无法让它按预期工作。我怎么能这样做？

Answer 1

使用UNION可以解决您的问题。像这样：

cannot make java calls from the compiler

如果您告诉我它们是什么，请使用您的表名和行调整代码。这种查询将返回如下内容：

SELECT
  WarehouseDB1.WarehouseID AS TheID,
  'A' AS TheSystem,
  WarehouseDB1.TheValue AS TheValue
FROM WarehouseDB1
UNION
SELECT
  WarehouseDB2.WarehouseID AS TheID,
  'B' AS TheSystem,
  WarehouseDB2.TheValue AS TheValue
FROM WarehouseDB2
UNION
  WarehouseDB3.WarehouseID AS TheID,
  'C' AS TheSystem,
  WarehouseDB3.TheValue AS TheValue
FROM WarehouseDB3

只要您的列名在每个查询中都匹配，就应该得到所需的结果。

Answer 2

使用这样的交叉连接：

// GET REQUEST TO RETRIEVE EVERY POST
const get = (url) => {
  return new Promise((resolve, reject) => {
    const xhttp = new XMLHttpRequest();

    xhttp.open('GET', url, true);

    xhttp.onload = () => {
      if (xhttp.status == 200) {
        resolve(JSON.parse(xhttp.response));
      } else {
        reject(xhttp.statusText);
      }
    };

    xhttp.onerror = () => {
      reject(xhttp.statusText);
    };

    xhttp.send();
  });
}

// DELETE SPECIFIC POST
const deletePostPromise = (url, postID) => {
  return new Promise((resolve, reject) => {
    const xhr = new XMLHttpRequest();

    xhr.open('POST', url, true);

    xhr.onload = () => {
      if (xhr.status == 200) {
        console.log('if (xhr.status == 200)');
        resolve();
      } else {
        reject(xhr.statusText);
      }
    };

    xhr.onerror = () => {
      reject(xhr.statusText);
    };

    xhr.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
    xhr.send(postID);
  });
}

// SUBMIT A NEW POST
const submitPost = (url, user_id, user_name, content) => {
  return new Promise((resolve, reject) => {
    const xhr = new XMLHttpRequest();

    xhr.open('POST', url, true);

    xhr.onload = () => {
      if (xhr.status == 200) {
        console.log('resolving');
        resolve();
      } else {
        reject(xhr.statusText);
      }
    };

    xhr.onerror = () => {
      reject(xhr.statusText);
    };

    xhr.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
    xhr.send(user_id, user_name, content);
  });
};

// RETURN THE NEWEST BLOG POST
const returnNewestPost = (url) => {
  return new Promise((resolve, reject) => {
    const xhr = new XMLHttpRequest();

    xhr.open('GET', url, true);

    xhr.onload = () => {
      if (xhr.status == 200) {
        console.log('resolving');
        resolve(JSON.parse(xhr.response));
      } else {
        reject(xhr.statusText);
      }
    };

    xhr.onerror = () => {
      reject(xhr.statusText);
    };

    xhr.send();
  });
}

结果：

create table table1 (field1 char(10));
create table table2 (field2 char(10));
create table table3 (field3 char(10));

insert into table1 values('value1');
insert into table2 values('value2');
insert into table3 values('value3');

select *
  from table1
  cross join table2
  cross join table3;

交叉连接将左侧的所有行与右侧的所有行连接起来。您将得到行的产品（table1行x table2行x table3行）。由于每个表只有一行，您将获得（1 x 1 x 1）= 1行。

将来自不同表的三列组合成一行

2 个答案: