# SDO_DAS_Relational::executeQuery

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SDO_DAS_Relational::executeQuery — Executes a given SQL query against a relational database and returns the results as a normalised data graph

### Description

SDO_DAS_Relational::executeQuery ( PDO `$database_handle` , string `$SQL_statement` [, array `$column_specifier` ] ) : SDODataObject
Warning

This function is EXPERIMENTAL. The behaviour of this function, its name, and surrounding documentation may change without notice in a future release of PHP. This function should be used at your own risk.

Executes a given query against the relational database, using the supplied PDO database handle. Uses the model that it built from the metadata to interpret the result set. Returns a data graph.

### Parameters

PDO_database_handle

  Constructed using the PDO extension. A typical line to construct a PDO database handle might look like this:

  `$dbh = new PDO("mysql:dbname=COMPANYDB;host=localhost",DATABASE_USER,DATABASE_PASSWORD);`
SQL_statement

  The SQL statement to be executed against the database.

column_specifier

  The Relational DAS needs to examine the result set and for every column, know which table and which column of that table it came from. In some circumstances it can find this information for itself, but sometimes it cannot. In these cases a column specifier is needed, which is an array that identifies the columns. Each entry in the array is simply a string in the form table-name.column_name.

  The column specifier is needed when there are duplicate column names in the database metadata. For example, in the database used within the examples, all the tables have both a id and a name column. When the Relational DAS fetches the result set from PDO it can do so with the PDO_FETCH_ASSOC attribute, which will cause the columns in the results set to be labelled with the column name, but will not distinguish duplicates. So this will only work when there are no duplicates possible in the results set.

  To summarise, specify a column specifier array whenever there is any uncertainty about which column could be from which table and only omit it when every column name in the database metadata is unique.

  All of the examples in the Examples use a column specifier. There is one example in the Scenarios directory of the installation that does not: that which works with just the employee table, and because it works with just one table, there can not exist duplicate column names.

### Return Values

Returns a data graph. Specifically, it returns a root object of a special type. Under this root object will be the data from the result set. The root object will have a multi-valued containment property with the same name as the application root type specified on the constructor, and that property will contain one or more data objects of the application root type.

In the event that the query returns no data, the special root object will still be returned but the containment property for the application root type will be empty.

### Errors/Exceptions

SDO_DAS_Relational::executeQuery() can throw an SDO_DAS_Relational_Exception if it is unable to construct the data graph correctly. This can occur for a number of reasons: for example if it finds that it does not have primary keys in the result set for all the objects. It also catches any PDO exceptions and obtains PDO diagnostic information which it includes in an SDO_DAS_Relational_Exception which it then throws.

### Examples

Please see the Examples section in the general information about the Relational DAS for many examples of calling this method.