使用 MySql 5.7 中的动态列引用从另一个表更新表

Question

我有两张表 NEW_TBL 和 CURRENT_TBL。

CURRENT_TBL 中的值需要更新，使其等于 NEW_TBL。两个表都有一个名为 tableId 的 PK，但 NEW_TBL 中的列并不总是匹配 CURRENT_TBL。我已经有了使架构相同所需的东西，但我需要一种基于动态列引用更新 CURRENT_TBL 值的方法。

这是我如何在 javascript 中完成此操作的人为示例。

起始表：

currentTable = [
  ['tableId','col2','col3','col4'],
  ['1','purple','blue','pink'],
  ['2','purple','red','orange'],
  ['3','green','yellow','purple']
];


newTable = [
  ['tableId','col2','col3','col4'],
  ['1','','blue','pink'],
  ['2','magenta','blue','pink'],
  ['4','grey','black','white']
];

功能：

function updateCurrentTable() {
  var currentHeader = currentTable[0];
  var newHeader = newTable[0];
  var currentValues = currentTable.slice(1);
  var newValues = newTable.slice(1);

  var newIdList = newValues.map(function(val){ // Get list of newTable ids
    return val[0];
  })

  var currentIdList = currentValues.map(function(val){ // Get list of newTable ids
    return val[0];
  })

  for (var newColumn = 0; newColumn<newHeader.length; newColumn++) { // Loop through new table columns
    var columnName = newHeader[newColumn];
    var newIdColumn = newHeader.indexOf('tableId');
    var currentColumnIndex = currentHeader.indexOf(columnName);
    var currentIdIndex = currentHeader.indexOf('tableId');

    if (columnName !== 'tableId') { // The tableId column is skipped because the id will never be altered

      for (var newRow = 0; newRow<newValues.length; newRow++) { // Loop through new table rows
        var newId = newValues[newRow][newIdColumn];
        var newValue = newValues[newRow][newColumn];

        if (currentIdList.indexOf(newId) < 0) { // If tableId exists in newTable but not in currentTable, add the row to currentTable
          currentValues.push(newValues[newRow]);
          currentIdList.push(newId); // Update the id list
        }

        for (var curRow =0; curRow < currentValues.length; curRow++) { // Loop through current table rows
          var currentId = currentValues[curRow][currentIdIndex];

          if (currentColumnIndex !== currentIdIndex) { // The tableId column is skipped because the id will never be altered

            if (newIdList.indexOf(currentId) < 0) { // If tableId exists in currentTable but not newTable, remove the row from currentTable
              currentValues.splice(curRow,1);
            } else if (newId === currentId) { // If the tableIds match, update the value in the current column
              currentValues[curRow][currentColumnIndex] = newValue; 
            } 
          }
        }
      }
    }
  }

  Logger.log(currentValues)
}

结果：

currentTable = [
  ['tableId','col2','col3','col4'],
  ['1','','blue','pink'],
  ['2','magenta','blue','pink'],
  ['4','grey','black','white']
];

有没有办法在 SQL 中完成上述操作？

谢谢！

Answer 1

我了解到您希望匹配 tableId 列上的表格，并使用来自 new_tbl 的相应值更新 current_tbl 中的 colHeader。

为此，您可以利用 MySQL update ... join ... set 语法：

update current_tbl c
inner join new_tbl n on c.tableId   = n.tableId
set c.colHeader = n.colHeader

Answer 2

我想出了一个解决方案，它动态创建 SQL 语句比较列的部分（即“currentTable.cost = newTable.cost”），然后使用动态列列表运行 UPDATE JOIN。

DELIMITER //
 CREATE PROCEDURE matchCurrentToNew()
 COMMENT 'Update currentTable to match newTable'
 BEGIN

    DECLARE num_rows INT;
    DECLARE col_name TINYTEXT;
    DECLARE concatStatement TINYTEXT;
    DECLARE concatFields TINYTEXT;
    DECLARE done TINYINT DEFAULT FALSE; 

    DECLARE col_names 
      CURSOR FOR
        SELECT column_name
        FROM INFORMATION_SCHEMA.COLUMNS
        WHERE table_name = 'TASKS'
        ORDER BY ordinal_position;

    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

    SET concatStatement = "";
    OPEN col_names;

    SELECT FOUND_ROWS() into num_rows;

    the_loop: LOOP

        FETCH NEXT FROM col_names    
        INTO col_name; 

        IF done THEN
          CLOSE col_names;
          LEAVE the_loop;
        END IF;

        IF col_name <> "UniqueId" AND col_name <> "ProjectId" THEN
            SET concatFields = CONCAT_WS("=",
                                     CONCAT_WS(".","currentTable",col_name),
                                     CONCAT_WS(".","newTable",col_name)
                                    );

            SET concatStatement = CONCAT(concatStatement,",",concatFields);         
        END IF;

    END LOOP the_loop;

    #     Remove comma at the beginning of the concatStatement string

    SET concatStatement = TRIM(LEADING "," FROM concatStatement);

    SET @sqlText = CONCAT(
      'UPDATE currentTable  
      JOIN newTable
      ON currentTable .UniqueId = newTable.UniqueId 
      AND currentTable .ProjectId = newTable.ProjectId
      SET ', concatStatement
    );

    PREPARE stmt FROM @sqlText;
    EXECUTE stmt;
    DEALLOCATE PREPARE stmt;

 END //
 DELIMITER ;