wuchong commented on a change in pull request #9335: [FLINK-13503][API] Add
contract in `LookupableTableSource` to specify the behavior when lookupKeys
contains null.
URL: https://github.com/apache/flink/pull/9335#discussion_r310451016
##########
File path:
flink-table/flink-table-common/src/main/java/org/apache/flink/table/sources/LookupableTableSource.java
##########
@@ -33,13 +33,33 @@
public interface LookupableTableSource<T> extends TableSource<T> {
/**
- * Gets the {@link TableFunction} which supports lookup one key at a
time.
+ * Gets the {@link TableFunction} which supports lookup one key at a
time. Calling `eval`
+ * method in the returned {@link TableFunction} means send a lookup
request to the TableSource.
+ *
+ * <p><strong>IMPORTANT:</strong>
+ * Lookup keys in a request may contain null value. When it happens, it
expects to lookup
+ * records with null value on the lookup key field.
+ * E.g., for a MySQL table with the following schema, send a lookup
request with null value
+ * on `age` field means to find students whose age are unknown
(CAUTION: It is equivalent to filter condition:
+ * `WHERE age IS NULL` instead of `WHERE age = null`).
+ *
+ * -----------------
+ * Table : Student
+ * -----------------
+ * id | LONG
+ * age | INT
+ * name | STRING
+ * -----------------
+ * For the external system which does not support null value (E.g,
HBase does not support null value on rowKey),
+ * it could throw an exception or discard the request when receiving a
request with null value on lookup key.
Review comment:
Please never throw an exception. We should discard the request because HBase
don't have null rowkeys.
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