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()ordbQueryFetchAllSA()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);