Function PreparedImpl.queryValue
Execute a prepared SQL SELECT command and returns a single value, the first column of the first row received.
If the query did not produce any rows, OR the rows it produced have zero columns,
this will return Nullable!Variant(), ie, null. Test for this with result.
If the query DID produce a result, but the value actually received is NULL,
then result will be FALSE, and result will produce a Variant
which CONTAINS null. Check for this with result.
If the SQL command does not produce a result set (such as INSERT/CREATE/etc),
then mysql will be thrown. Use
exec instead for such commands.
If there are long data items among the expected result columns you can use the csa param to specify that they are to be subject to chunked transfer via a delegate.
Prototype
std
ColumnSpecialization[] csa = null
);
Parameters
| Name | Description |
|---|---|
| csa | An optional array of ColumnSpecialization structs. |
Returns
Nullable!Variant: This will be null (check via Nullable.isNull) if the query resulted in an empty result set.