Added DISTINCT on Zend\Db\Sql\Select

[twmobius]

I've added DISTINCT on Zend\Db\Sql\Select as a new method to support queries like 'SELECT DISTINCT * FROM foo'

Also updated the unit tests to pass after the changes and added a new test for the DISTINCT feature.

This fixes partially #2509

[marc-mabe]

Shouldn't it be false by default?

[twmobius]

Yes I guess it makes more sense.

[marc-mabe]

Argument to set to true / false

[marc-mabe]

Because MySQL supports more than that flags I would prefer to implement it as list of flags addable to a select like it was done by propel: [add|has|remove]Modifier() and [get|reset|add|remove]Modifiers().
Than it's possible to create all selects like SELECT [{MODIFIERS}] ...

Other servers supports at least the DISTINCT and ALL flags

[twmobius]

Well this is probably more correct, however I've tried to replicate the behaviour of Zend_Db_Select of ZF1.

MSSQL has also the TOP %d modifier instead of LIMIT.

[ralphschindler]

So that "thing" is called a "Set Quantifier", and I think the API should reflect that probably:

public function quantifier($quantifier = 'ALL')
{

}

quantifiers can be strings (literal expressions), predicates or arrays

DISTINCT and ALL are part of SQL92, but I don't think we should make a list as most server implementations will have their own. Usage would look like:

$select->quantifier('DISTINCT');

or for sql server, for example:
$select->quantifier(array('TOP ?' => 10));

Thoughts?

[marc-mabe]

@ralphschindler If this isn't in conflict with limit it looks good to me.

$select->quantifier(array('TOP ?' => 10));
$select->limit(500);
// = ?

[ralphschindler]

From a dialect/sql parser standpoint, there is no conflict. Now, for Sql Server, I can't promise the engine won't barf when it tries to build a query plan. Also, limit/offset is a sensitive subject on Sql Server specifically with regards to whatever version you're using. Sql Server got limit/offset support in Denali (latest version).

using $select->quantifier(array('TOP ?' => 10)); is using a SQL Server specific quantifier anyway, in much the same way that you could use any number of MySQL specific functions through an expression.

[weierophinney]

@twmobius @marc-mabe and @ralphschindler Can the three of you come up with a plan of action, please? It looks like a different direction needs to be taken, but the solution is also getting quite out-of-date with master; we either need to move forward or close...

[twmobius]

Sorry for taking too long to respond, but I've been really busy lately.
I like the approach proposed by @ralphschindler. I'll see if I can craft something up today.

[twmobius]

I started tackling with this and first of, I see that there is a problem with having a Predicate\Expression to supply quantifiers like 'TOP %d'. The processExpression method quotes the values in an expression resulting in TOP [10] instead of the Literal TOP 10 that Sql Server expects.

Also to my understanding ALL | DISTINCT are mutually exclusive, therefore there shouldn't be any need for multiple quantifiers. (array as parameter)

[ralphschindler]

@twmobius, I think all quantifiers are mutually exclusive, no? I will work up a PR for this.

[twmobius]

@ralphschindler Well I've looked up transact-sql and you could have DISTINCT TOP(%d) but that could still be one single quantifier.

[ralphschindler]

Ok, to start, lets go with a single quantifier, let me take a stab at this.

[ralphschindler]

Please see the implementation in #3682