D-talk

Drop empty columns with dynamically defined columns and tables

2010-08-17T11:54:00Z

For a migration process I wanted to build in extra validation in some destructive MySQL queries, to eliminate the risk that data might be lost. Of course all data is back-upped, but I rather be safe then sorry.

This is fairly straight forward, create a stored procedure and perform an ALTER statement whenever the previously defined criteria have been met. But I wanted to define a single procedure rather then create one for every table I had to drop columns from. And since you can't simply use variables for column/table names, you have to improvise a little. I came up with the following:

-- Defining the "drop empty column" SP
DELIMITER @@
DROP PROCEDURE IF EXISTS drop_empty_column @@
CREATE PROCEDURE drop_empty_column(
IN itable VARCHAR(50),
IN icolumn VARCHAR(50),
OUT succeeded INT
)
BEGIN

SET @amount = -1;
SET @itable = itable;
SET @icolumn = icolumn;

-- Build the query, with dynamic table and column. Store the result in @amount
SELECT CONCAT('SELECT COUNT(', @icolumn ,') INTO @amount FROM ', @itable ,' WHERE(', @icolumn ,' IS NOT NULL OR ', @icolumn ,' != "");') INTO @testSql;
PREPARE testSqlStmt FROM @testSql;

-- Execute
EXECUTE testSqlStmt;

-- Check if we have 0 rows, else we still have data and we can't drop.
IF @amount = 0 THEN

-- Build the query
SELECT CONCAT('ALTER TABLE ', @itable ,' DROP COLUMN ', @icolumn ,';') INTO @alterSql;

-- Execute
PREPARE alterSqlStmt FROM @alterSql;
EXECUTE alterSqlStmt;

-- Update the status
SELECT 1 INTO succeeded;
ELSE
SELECT 0 INTO succeeded;
END IF;

END@@
DELIMITER ;

-- Conditionally drop the column "deprecated_column" from table "some_table"
CALL drop_empty_column('some_table', 'deprecated_column', @succeeded);

-- Show the status
SELECT @succeeded;

-- Cleanup
DROP PROCEDURE IF EXISTS drop_empty_column;

I'm fairly positive that this could be done in a much better way then that I'm doing here, but this works too. Simply repeat the CALL drop_empty_column(..) for every table/column combination you want to DROP and update the definition of an "empty column" to what you want. Currently it drops the column only if the values contain nothing other then NULL or "" (empty string) values.

Further reading:

What do you get when you mix; MSSQL, PDO and uniqueidentifier?

2010-06-08T19:58:00Z

You get NULL!

Well you get NULL when you don't cast. Say for example you do the following:

$dbh = new PDO([..]);
$stmt = $dbh->prepare('SELECT accountid FROM dbo.Account');
$stmt->execute();

echo $stmt->fetchColumn(); // NULL

But when you do the following:

$stmt = $dbh->prepare('SELECT CAST(accountid AS varchar(36)) accountid FROM dbo.Account');
$stmt->execute();

echo $stmt->fetchColumn(); // "F05C92A1-3119-4206-A123-49A759AC99FB"

I didn't think the casting would be necessary, since according to the manual: http://msdn.microsoft.com/en-us/library/aa226054(SQL.80).aspx the datatype 'uniqueidentifier' has implicit casts with multiple data-types. But I guess it's just one of those things...

Connecting from PHP on a non Microsoft OS to MSSQL with a domain account

2010-06-04T05:24:00Z

I was asked to create a web interface front-end with Microsoft Dynamics CRM as back-end. But I had some troubles setting up the connection, since it has to be done using a domain logon. This doesn't have to be a problem at all, unless your configuration is wrong! In this article I'll explain a few things and point you in the right direction when you have login problems.

As stated earlier, the server running the PHP installation is not Microsoft. In this case a AS400 installation, but it could've been a Linux installation also. I'm using PDO for this article and PHP version 5.2.11. Even if you don't want to use PDO, I recommend using it only for debugging (if possible) since that will give you *most likely* more debug information then the mssql_* family.

When using PDO with a MS-SQL database, you'll need to supply "dblib" as driver and DBLib uses FreeTDS as underlaying library. FreeTDS can be a source of troubles when you're trying to connect, if not configured properly. So I'll kick-off with a little information about it. Don't skip it if you have login problems!

Continue reading "Connecting from PHP on a non Microsoft OS to MSSQL with a domain account"

PHPUnit conditional test based on a PHP version

2010-04-19T14:47:00Z

I had a problem with running test cases on multiple CI environments, where one of the two runs on PHP 5.2 and the other on PHP 5.3. This basically meant that all our pretty PHP 5.3 code caused the builds to fail on the 5.2 only machine. To solve this problem I needed a way to skip tests when the PHP version was less then 5.3.0. Besides the reason I needed this for a -less then ideal- setup. This can also be a generic way to skip certain tests, based on a PHP version.

class someTest extends PHPUnit_Framework_TestCase
{
public function setUp()
{
// Testing if we are dealing with version 5.3.0 or higher
if (!version_compare(PHP_VERSION, '5.3.0', '>=')) {
$this->markTestSkipped('Invalid PHP version, unable to run tests.');
}
}

public function test_testFoo()
{
// .. some awesum test case .. \\
}
}

You can also use the cool @depends annotation of PHPUnit and put the version logic in a test. This has my preference, but it's not always possible. In case you have some code that simply can't be parsed by the older PHP engines.

If you know a better way to do this, please share!