SDO _DAS _Relational: : executeQuery

Eerste pagina van Manuel PHP  Inhoudsopgave Haut

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.