dbHasFeature

Purpose

Returns a 1 if the database supports the specified feature.

Format

ret = dbHasFeature(db_id, feature)
Parameters
  • db_id (scalar) – database connection index number.

  • feature (scalar) –

    one of the following predefined scalars:

    Supported

    Define

    Description

    Yes

    DB_TRANSACTIONS

    Whether the driver supports SQL transactions.

    Yes

    DB_QUERY_SIZE

    Whether the database is capable of reporting the size of a query. Note that some databases do not support returning the size (i.e. number of rows returned) of a query. This can affect the performance when fetching results using functions like dbQueryFetchAllM() or dbQueryFetchAllSA()

    No

    DB_BLOB

    Whether the driver supports Binary Large Object fields.

    No

    DB_UNICODE

    Whether the driver supports Unicode strings if the database server does.

    Yes

    DB_PREPARED_QUERIES

    Whether the driver supports prepared query execution.

    Yes

    DB_NAMED_PLACEHOLDERS

    Whether the driver supports the use of named placeholders.

    Yes

    DB_POSITIONAL_PLACEHOLDERS

    Whether the driver supports the use of positional placeholders.

    Yes

    DB_LAST_INSERT_ID

    Whether the driver supports returning the Id of the last touched row.

    Yes

    DB_BATCH_OPERATIONS

    Whether the driver supports batched operations, see dbExecQueries().

    Yes

    DB_SIMPLE_LOCKING

    Whether the driver disallows a write lock on a table while other queries have a read lock on it.

    Yes

    DB_LOW_PRECISION_NUMBERS

    Whether the driver allows fetching numerical values with low precision.

    No

    DB_EVENT_NOTIFICATIONS

    Whether the driver supports database event notifications.

    Yes

    DB_FINISH_QUERY

    Whether the driver can do any low-level resource cleanup when dbQueryFinish() is called.

    No

    DB_MULTIPLE_RESULT_SETS

    Whether the driver can access multiple result sets returned from batched statements or stored procedures.

    No

    DB_CANCEL_QUERY

    Whether the driver allows cancelling a running query.

Returns

ret (scalar) – 1 if the database supports the specified feature, or 0 if not.

Examples

// Set database connection index number
db_id = dbAddDatabase("MYSQL");

// Create empty query
qid = dbCreateQuery(db_id);

/*
** Use dbHasFeature to set up a
** conditional query
*/
if dbHasFeature(db_id, DB_NAMED_PLACEHOLDERS);
     dbQueryPrepare(qid, "SELECT * FROM GDP WHERE COUNTRY = :country");
     dbQueryBindValue(qid, ":country", "USA");
else;
     dbQueryPrepare(qid, "SELECT * FROM GDP WHERE COUNTRY = ?");
     dbQueryAddBindValue(qid, "USA");
endif;

dbQueryExecPrepared(qid);

Remarks

Note that some databases need to be opened with dbOpen() before this can be determined.