MySQL Join two tables with comma separated values

问题

I have 2 tables as below

Notes Table

╔══════════╦═════════════════╗
║ nid      ║    forDepts     ║
╠══════════╬═════════════════╣
║ 1        ║ 1,2,4           ║
║ 2        ║ 4,5             ║
╚══════════╩═════════════════╝

Positions Table

╔══════════╦═════════════════╗
║ id       ║    name         ║
╠══════════╬═════════════════╣
║ 1        ║ Executive       ║
║ 2        ║ Corp Admin      ║
║ 3        ║ Sales           ║
║ 4        ║ Art             ║
║ 5        ║ Marketing       ║
╚══════════╩═════════════════╝

I am looking to query my Notes table and associate the \'forDepts\' column with values from the Positions table.

The output should be:

    ╠══════════╬════════════════════════════╣
    ║ 1        ║ Executive, Corp Admin, Art ║
    ║ 2        ║ Art, Marketing             ║
    ╚══════════╩════════════════════════════╝

I know that the database should be normalized but I cannot change the database structure for this project.

This is going to be used to export a excel file with the code below.

<?PHP

    $dbh1 = mysql_connect($hostname, $username, $password); 
    mysql_select_db(\'exAdmin\', $dbh1);


    function cleanData(&$str)
  {
    $str = preg_replace(\"/\\t/\", \"\\\\t\", $str);
    $str = preg_replace(\"/\\r?\\n/\", \"\\\\n\", $str);
    if(strstr($str, \'\"\')) $str = \'\"\' . str_replace(\'\"\', \'\"\"\', $str) . \'\"\';
  }

    $filename = \"eXteres_summary_\" . date(\'m/d/y\') . \".xls\";

    header(\"Content-Disposition: attachment; filename=\\\"$filename\\\"\");
    header(\"Content-Type: application/vnd.ms-excel\");
    //header(\"Content-Type: text/plain\");

    $flag = false;


    $result = mysql_query(
    \"SELECT p.name, c.company, n.nid, n.createdOn, CONCAT_WS(\' \',c2.fname,c2.lname), n.description 
     FROM notes n 
     LEFT JOIN Positions p ON p.id = n.forDepts
     LEFT JOIN companies c ON c.userid = n.clientId
     LEFT JOIN companies c2 ON c2.userid = n.createdBy\"
     , $dbh1);



    while(false !== ($row = mysql_fetch_assoc($result))) {
        if(!$flag) {
            $colnames = array(
                \'Created For\' => \"Created For\",
                \'Company\' => \"Company\",
                \'Case ID\' => \"Case ID\",
                \'Created On\' => \"Created On\",
                \'Created By\' => \"Created By\",
                \'Description\' => \"Description\"
            );
            // display field/column names as first row
            echo implode(\"\\t\", array_keys($colnames)) . \"\\r\\n\";
            $flag = true;
    }


        $row[\'createdOn\'] = date(\'m-d-Y | g:i a\', strtotime($row[\'createdOn\']));

    array_walk($row, \'cleanData\');
    echo implode(\"\\t\", array_values($row)) . \"\\r\\n\";
  }
  exit;

  ?>

This code outputs only the first value of \'forDepts\'

Exa: Executive (instead of Executive, Corp Admin, Art)

Can this be accomplished by CONCAT or FIND_IN_SET?

Please help! Thanks in advance!

回答1:

SELECT  a.nid,
        GROUP_CONCAT(b.name ORDER BY b.id) DepartmentName
FROM    Notes a
        INNER JOIN Positions b
            ON FIND_IN_SET(b.id, a.forDepts) > 0
GROUP   BY a.nid

• SQLFiddle Demo

回答2:

Table 1
╔══════════╦═════════════════╗
║ nid      ║    forDepts     ║
╠══════════╬═════════════════╣
║ 1        ║ 1,2,4           ║
║ 2        ║ 4,5             ║
╚══════════╩═════════════════╝
Table 2
╔══════════╦═════════════════╗
║ id       ║    name         ║
╠══════════╬═════════════════╣
║ 1        ║ Executive       ║
║ 2        ║ Corp Admin      ║
║ 3        ║ Sales           ║
║ 4        ║ Art             ║
║ 5        ║ Marketing       ║
╚══════════╩═════════════════╝

SELECT * FROM table1 as t1 LEFT JOIN table2 as t2 ON find_in_set(t2.id, 
t1.forDepts)

Output 

 ╠══════════╬════════════════════════════╣
 ║ 1        ║ Executive, Corp Admin, Art ║
 ║ 2        ║ Art, Marketing             ║
 ╚══════════╩════════════════════════════╝

来源：https://stackoverflow.com/questions/19101550/mysql-join-two-tables-with-comma-separated-values