नोट
इस पेज तक पहुँच के लिए प्रमाणन की आवश्यकता होती है. आप साइन इन करने या निर्देशिकाओं को बदलने का प्रयास कर सकते हैं.
इस पेज तक पहुँच के लिए प्रमाणन की आवश्यकता होती है. आप निर्देशिकाओं को बदलने का प्रयास कर सकते हैं.
Applies to: 
Databricks SQL Databricks Runtime 12.0 and above
Adds a watermark to a relation in a select statement. The WATERMARK clause only applies to queries on stateful streaming data, which include stream-stream joins and aggregation.
Syntax
from_item
{ table_name [ TABLESAMPLE clause ] [ watermark_clause ] [ table_alias ] |
JOIN clause |
[ LATERAL ] table_valued_function [ table_alias ] |
VALUE clause |
[ LATERAL ] ( query ) [ TABLESAMPLE clause ] [ watermark_clause ] [ table_alias ] }
watermark_clause
WATERMARK named_expression DELAY OF interval
Parameters
-
An expression that provides a value of type
timestamp. The expression must be either a reference to the existing column, or a deterministic transformation against existing column(s). The expression adds a column of timestamp type which is used to track the watermark. The added column is available to query. -
An interval literal that defines the delay threshold of the watermark. Must be a positive value less than a month.
Examples
-- Creating a streaming table performing time window row count, with defining watermark from existing column
> CREATE OR REFRESH STREAMING TABLE window_agg_1
AS SELECT window(ts, '10 seconds') as w, count(*) as CNT
FROM
STREAM stream_source WATERMARK ts DELAY OF INTERVAL 10 SECONDS AS stream
GROUP BY window(ts, '10 seconds');
-- Creating a streaming table performing time window row count, with deriving a new timestamp column to define watermark
> CREATE OR REFRESH STREAMING TABLE window_agg_2
AS SELECT window(ts, '10 seconds') as w, count(*) as CNT
FROM
STREAM stream_source WATERMARK to_timestamp(ts_str) AS ts DELAY OF INTERVAL 10 SECONDS AS stream
GROUP BY window(ts, '10 seconds');