Airblader commented on a change in pull request #16046:
URL: https://github.com/apache/flink/pull/16046#discussion_r649080052
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File path:
flink-table/flink-table-api-java/src/main/java/org/apache/flink/table/api/Expressions.java
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@@ -211,6 +211,27 @@ public static ApiExpression currentTimestamp() {
return apiCall(BuiltInFunctionDefinitions.CURRENT_TIMESTAMP);
}
+ /**
+ * Returns the current watermark for the given rowtime attribute, or
{@code NULL} if no
+ * watermark has been emitted yet.
+ *
+ * <p>The function returns the watermark with the same type as the rowtime
attribute, but with
+ * an adjusted precision of 3. For example, if the rowtime attribute is
{@link
+ * DataTypes#TIMESTAMP_LTZ(int) TIMESTAMP_LTZ(9)}, the function will
return {@link
+ * DataTypes#TIMESTAMP_LTZ(int) TIMESTAMP_LTZ(3)}.
+ *
+ * <p>If no watermark has been emitted yet, the function will return
{@code NULL}. Users must
+ * take care of this when comparing against it, e.g. in order to filter
out late data you can
+ * use
+ *
+ * <pre>{@code
+ * WHERE CURRENT_WATERMARK(ts) IS NULL OR ts > CURRENT_WATERMARK(ts)
+ * }</pre>
+ */
+ public static ApiExpression currentWatermark(Object rowtimeAttribute) {
Review comment:
I think I like the prefix version a bit better here (though it's a close
call). The advantages of the infix notation are really just all of the general
ones – nothing that applies to this scenario, specifically, I think. Since the
watermark isn't really part of the time attribute, but rather just defined
using it, I slightly prefer the prefix version.
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