Function PreparedImpl.queryValue
Executes a one-off SQL command and returns a single value: The the first column of the first row received. Useful for the case where you expect a (possibly empty) result set, and you're either only expecting one value, or only care about the first value.
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.
Use this method when you will use the same command repeatedly. It will throw if the specified command does not produce a result set.
If there are long data items among the expected result columns you can 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.