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 different data.
What's the best way to diff these two tables?
To be more precise, I'm trying to figure out a simple SQL query that tells me if data from one row in t1 is different from the data from the corresponding row in t2
It appears I cannot use the intersect nor minus. When I try
SELECT * FROM robot intersect SELECT * FROM tbd_robot
I get an error code:
[Error Code: 1064, SQL State: 42000] You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'SELECT * FROM tbd_robot' at line 1
Am I doing something syntactically wrong? If not, is there another query I can use?
Edit: Also, I'm querying through a free version DbVisualizer. Not sure if that might be a factor.
The answer is
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
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
Problem below, is to compare table before and after i do big update!.
If you use Linux, you can use commands as follow:
In terminal,
mysqldump -hlocalhost -uroot -p schema_name_here table_name_here > /home/ubuntu/database_dumps/dump_table_before_running_update.sql
mysqldump -hlocalhost -uroot -p schema_name_here table_name_here > /home/ubuntu/database_dumps/dump_table_after_running_update.sql
diff -uP /home/ubuntu/database_dumps/dump_some_table_after_running_update.sql /home/ubuntu/database_dumps/dump_table_before_running_update.sql > /home/ubuntu/database_dumps/diff.txt
You will need online tools for
- Formatting SQL exported from the dumps,
e.g http://www.dpriver.com/pp/sqlformat.htm [Not the best I've seen]
We have diff.txt, you have to take manually the + - showing inside, which is 1 line of insert statements, that has the values.
Do diff online for the 2 lines - & + in diff.txt, past them in online diff tool
e.g https://www.diffchecker.com [you can save and share it, and has no limit on file size!]
Note: be extra careful if its sensitive/production data!
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)
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.
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!";
}
}
?>
Source: Stackoverflow.com