ZF3 Create SELECT query from expression - php

Question

I want to create a ZF3 \Zend\Db\Sql\Select object where table is pgsql expression:
generate_series('2017-01-01'::date, '2017-02-01'::date, '1 day'::interval)
but if I pass expression as \Zend\Db\Sql\Expression object, like this:
$select = new \Zend\Db\Sql\Select();
$select->from(['dd' => new \Zend\Db\Sql\Expression("generate_series('2017-01-01'::date, '2017-02-01'::date, '1 day'::interval)")]);
I'm getting following error:
Catchable fatal error: Object of class Zend\Db\Sql\Expression could not be converted to string
but if I pass my expression as string, it's getting automatically wrapped and looks like this:
SELECT "dd".* FROM "generate_series('2017-01-01'::date, '2017-02-01'::date, '1 day'::interval)" AS "dd"
which is of course wrong. Is it possible to achieve without overwriting ZF3 Select class?

Answer 1

Select::form() method takes table name as its argument. You may try this way:
$select = new \Zend\Db\Sql\Select();
$select->columns(['AliasName' => new \Zend\Db\Sql\Expression("YourExpression")]);
This would produce following query:
SELECT YourExpression AS "AliasName"
Updated
The working example of the above method is down here. First, create an instance of database adapter providing database information. In this case, we are using PDO driver for Postgresql.
$adapter = new \Zend\Db\Adapter\Adapter([
'driver' => 'Pdo_Pgsql',
'database' => 'YourDatabaseName',
'username' => 'YourDatabaseUsername',
'password' => 'PasswordForDatabase',
]);
Next up, we are going to create an another instance of Sql::class from zend-db component. It is not mandatory if you are using TableGateway::class in your controller action.
$sql = new \Zend\Db\Sql\Sql($adapter);
Now here is the one you want, the Select object, which we are creating from the previous Sql object. Here we are also querying through zend-db's Expression::class to generate some date series.
$select = $sql->select();
$select->columns(["dd" => new \Zend\Db\Sql\Expression("generate_series('2007-02-01'::timestamp, '2007-03-01'::timestamp, '1 day'::interval)")]);
If we output the sql as string we would then get as the following
SELECT generate_series('2007-02-01'::timestamp, '2007-03-01'::timestamp, '1 day'::interval) AS "dd"
As we are using PDO driver for postgresql, we would prepare the statement at the moment, and finally execute the sql.
$statement = $sql->prepareStatementForSqlObject($select);
$results = $statement->execute();
If we output the results we fetched we would then get a series of dates as the following
foreach ($results as $row) {
print $row['dd'] ."</br>";
}
// Outputs
2007-02-01 00:00:00
2007-02-02 00:00:00
2007-02-03 00:00:00
2007-02-04 00:00:00
...
Hope this would help you!