compare differences between two tables in mysql

Question

Same as oracle diff: how to compare two tables? except in mysql.

Suppose I have two tables, t1 and t2 which are identical in layout but which may contain

Answer 1

 select t1.user_id,t2.user_id 
 from t1 left join t2 ON t1.user_id = t2.user_id 
 and t1.username=t2.username 
 and t1.first_name=t2.first_name 
 and t1.last_name=t2.last_name

try this. This will compare your table and find all matching pairs, if any mismatch return NULL on left.

Answer 2

Based on Haim's answer here's a simplified example if you're looking to compare values that exist in BOTH tables, otherwise if there's a row in one table but not the other it will also return it....

Took me a couple of hours to figure out. Here's a fully tested simply query for comparing "tbl_a" and "tbl_b"

SELECT ID, col
FROM
(
    SELECT
    tbl_a.ID, tbl_a.col FROM tbl_a
    UNION ALL
    SELECT
    tbl_b.ID, tbl_b.col FROM tbl_b
) t
WHERE ID IN (select ID from tbl_a) AND ID IN (select ID from tbl_b)
GROUP BY
ID, col
HAVING COUNT(*) = 1
 ORDER BY ID

So you need to add the extra "where in" clause:

WHERE ID IN (select ID from tbl_a) AND ID IN (select ID from tbl_b)

---

Also:

For ease of reading if you want to indicate the table names you can use the following:

SELECT tbl, ID, col
FROM
(
    SELECT
    tbl_a.ID, tbl_a.col, "name_to_display1" as "tbl" FROM tbl_a
    UNION ALL
    SELECT
    tbl_b.ID, tbl_b.col, "name_to_display2" as "tbl" FROM tbl_b
) t
WHERE ID IN (select ID from tbl_a) AND ID IN (select ID from tbl_b)
GROUP BY
ID, col
HAVING COUNT(*) = 1
 ORDER BY ID

Answer 3

Based on Haim's answer I created a PHP code to test and display all the differences between two databases. This will also display if a table is present in source or test databases. You have to change with your details the <> variables content.

<?php

    $User = "<DatabaseUser>";
    $Pass = "<DatabasePassword>";
    $SourceDB = "<SourceDatabase>";
    $TestDB = "<DatabaseToTest>";

    $link = new mysqli( "p:". "localhost", $User, $Pass, "" );

    if ( mysqli_connect_error() ) {

        die('Connect Error ('. mysqli_connect_errno() .') '. mysqli_connect_error());

    }

    mysqli_set_charset( $link, "utf8" );
    mb_language( "uni" );
    mb_internal_encoding( "UTF-8" );

    $sQuery = 'SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA="'. $SourceDB .'";';

    $SourceDB_Content = query( $link, $sQuery );

    if ( !is_array( $SourceDB_Content) ) {

        echo "Table $SourceDB cannot be accessed";
        exit(0);

    }

    $sQuery = 'SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA="'. $TestDB .'";';

    $TestDB_Content = query( $link, $sQuery );

    if ( !is_array( $TestDB_Content) ) {

        echo "Table $TestDB cannot be accessed";
        exit(0);

    }

    $SourceDB_Tables = array();
    foreach( $SourceDB_Content as $item ) {
        $SourceDB_Tables[] = $item["TABLE_NAME"];
    }

    $TestDB_Tables = array();
    foreach( $TestDB_Content as $item ) {
        $TestDB_Tables[] = $item["TABLE_NAME"];
    }
    //var_dump( $SourceDB_Tables, $TestDB_Tables );
    $LookupTables = array_merge( $SourceDB_Tables, $TestDB_Tables );
    $NoOfDiscrepancies = 0;
    echo "

    <table border='1' width='100%'>
    <tr>
        <td>Table</td>
        <td>Found in $SourceDB (". count( $SourceDB_Tables ) .")</td>
        <td>Found in $TestDB (". count( $TestDB_Tables ) .")</td>
        <td>Test result</td>
    <tr>

    ";

    foreach( $LookupTables as $table ) {

        $FoundInSourceDB = in_array( $table, $SourceDB_Tables ) ? 1 : 0;
        $FoundInTestDB = in_array( $table, $TestDB_Tables ) ? 1 : 0;
        echo "

    <tr>
        <td>$table</td>
        <td><input type='checkbox' ". ($FoundInSourceDB == 1 ? "checked" : "") ."></td> 
        <td><input type='checkbox' ". ($FoundInTestDB == 1 ? "checked" : "") ."></td>   
        <td>". compareTables( $SourceDB, $TestDB, $table ) ."</td>  
    </tr>   
        ";

    }

    echo "

    </table>
    <br><br>
    No of discrepancies found: $NoOfDiscrepancies
    ";


    function query( $link, $q ) {

        $result = mysqli_query( $link, $q );

        $errors = mysqli_error($link);
        if ( $errors > "" ) {

            echo $errors;
            exit(0);

        }

        if( $result == false ) return false;
        else if ( $result === true ) return true;
        else {

            $rset = array();

            while ( $row = mysqli_fetch_assoc( $result ) ) {

                $rset[] = $row;

            }

            return $rset;

        }

    }

    function compareTables( $source, $test, $table ) {

        global $link;
        global $NoOfDiscrepancies;

        $sQuery = "

    SELECT column_name,ordinal_position,data_type,column_type FROM
    (
        SELECT
            column_name,ordinal_position,
            data_type,column_type,COUNT(1) rowcount
        FROM information_schema.columns
        WHERE
        (
            (table_schema='$source' AND table_name='$table') OR
            (table_schema='$test' AND table_name='$table')
        )
        AND table_name IN ('$table')
        GROUP BY
            column_name,ordinal_position,
            data_type,column_type
        HAVING COUNT(1)=1
    ) A;    

        ";

        $result = query( $link, $sQuery );

        $data = "";
        if( is_array( $result ) && count( $result ) > 0 ) {

            $NoOfDiscrepancies++;
            $data = "<table><tr><td>column_name</td><td>ordinal_position</td><td>data_type</td><td>column_type</td></tr>";

            foreach( $result as $item ) {

                $data .= "<tr><td>". $item["column_name"] ."</td><td>". $item["ordinal_position"] ."</td><td>". $item["data_type"] ."</td><td>". $item["column_type"] ."</td></tr>";

            }

            $data .= "</table>";

            return $data;

        }
        else {

            return "Checked but no discrepancies found!";

        }

    }

?>

Answer 4

You can construct the intersection manually using UNION. It's easy if you have some unique field in both tables, e.g. ID:

SELECT * FROM T1
WHERE ID NOT IN (SELECT ID FROM T2)

UNION

SELECT * FROM T2
WHERE ID NOT IN (SELECT ID FROM T1)

If you don't have a unique value, you can still expand the above code to check for all fields instead of just the ID, and use AND to connect them (e.g. ID NOT IN(...) AND OTHER_FIELD NOT IN(...) etc)

Answer 5

I found another solution in this link

SELECT MIN (tbl_name) AS tbl_name, PK, column_list
FROM
 (
  SELECT ' source_table ' as tbl_name, S.PK, S.column_list
  FROM source_table AS S
  UNION ALL
  SELECT 'destination_table' as tbl_name, D.PK, D.column_list
  FROM destination_table AS D 
)  AS alias_table
GROUP BY PK, column_list
HAVING COUNT(*) = 1
ORDER BY PK

Answer 6

INTERSECT needs to be emulated in MySQL:

SELECT  'robot' AS `set`, r.*
FROM    robot r
WHERE   ROW(r.col1, r.col2, …) NOT IN
        (
        SELECT  col1, col2, ...
        FROM    tbd_robot
        )
UNION ALL
SELECT  'tbd_robot' AS `set`, t.*
FROM    tbd_robot t
WHERE   ROW(t.col1, t.col2, …) NOT IN
        (
        SELECT  col1, col2, ...
        FROM    robot
        )