类别：

系统函数 （系统信息）

SYSTEM$SET_RETURN_VALUE

显式设置任务的返回值。

在 任务图 中，任务可以调用此函数来设置返回值。将此任务标识为前置任务的另一个任务（在任务定义中使用 AFTER 关键字）可以使用 SYSTEM$GET_PREDECESSOR_RETURN_VALUE 检索前置任务设置的返回值。

语法

SYSTEM$SET_RETURN_VALUE( '<string_expression>' )
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string_expression 实参的值可以是字符串字面量或变量；例如 SYSTEM$SET_RETURN_VALUE(:VARIABLE)。

实参

string_expression

要设置为返回值的字符串。字符串大小必须 <= 10 kB（使用 UTF8 编码时）。

示例

创建设置返回值的任务。创建在前置任务任务完成后运行的第二个子任务。子任务检索由前置任务设置的返回值（通过调用 SYSTEM$GET_PREDECESSOR_RETURN_VALUE）并将其插入表行：

-- Create a table to store the return values.
CREATE OR REPLACE TABLE return_values (str VARCHAR);

-- Create a task that sets the return value for the task.
CREATE TASK set_return_value
  WAREHOUSE=return_task_wh
  SCHEDULE='1 MINUTE'
  AS
    CALL SYSTEM$SET_RETURN_VALUE('The quick brown fox jumps over the lazy dog');

-- Create a task that identifies the first task as the predecessor task and retrieves the return value set for that task.
CREATE TASK get_return_value
  WAREHOUSE=return_task_wh
  AFTER set_return_value
  AS
    INSERT INTO return_values VALUES(SYSTEM$GET_PREDECESSOR_RETURN_VALUE());


-- Note that if there are multiple predecessor tasks that are enabled, you must specify the name of the task to retrieve the return value for that task.
CREATE TASK get_return_value_by_pred
  WAREHOUSE=return_task_wh
  AFTER set_return_value
  AS
    INSERT INTO return_values VALUES(SYSTEM$GET_PREDECESSOR_RETURN_VALUE('SET_RETURN_VALUE'));

-- Resume task (using ALTER TASK ... RESUME).
-- Wait for task to run on schedule.

SELECT DISTINCT(str) FROM return_values;
+-----------------------------------------------+
|                      STR                      |
+-----------------------------------------------+
|  The quick brown fox jumps over the lazy dog  |
+-----------------------------------------------+

SELECT DISTINCT(RETURN_VALUE)
  FROM TABLE(information_schema.task_history())
  WHERE RETURN_VALUE IS NOT NULL;


+-----------------------------------------------+
|                  RETURN_VALUE                 |
+-----------------------------------------------+
|  The quick brown fox jumps over the lazy dog  |
+-----------------------------------------------+
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示例 2：使用单独的存储过程调用

与第一个示例类似，但设置任务的返回值，并通过调用单独的存储过程来检索它：

-- Create a table to store the return values.
CREATE OR REPLACE TABLE return_values_sp (str VARCHAR);

-- Create a stored procedure that sets the return value for the task.
CREATE OR REPLACE PROCEDURE set_return_value_sp()
RETURNS STRING
LANGUAGE JAVASCRIPT
EXECUTE AS CALLER
AS $$
var stmt = snowflake.createStatement({sqlText:`CALL SYSTEM$SET_RETURN_VALUE('The quick brown fox jumps over the lazy dog');`});
  var res = stmt.execute();
$$;

-- Create a stored procedure that inserts the return value for the predecessor task into the 'return_values_sp' table.
CREATE OR REPLACE PROCEDURE get_return_value_sp()
RETURNS STRING
LANGUAGE JAVASCRIPT
EXECUTE AS CALLER
AS $$
var stmt = snowflake.createStatement({sqlText:`INSERT INTO return_values_sp VALUES(SYSTEM$GET_PREDECESSOR_RETURN_VALUE());`});
var res = stmt.execute();
$$;

-- Create a task that calls the set_return_value stored procedure.
CREATE TASK set_return_value_t
WAREHOUSE=warehouse1
SCHEDULE='1 MINUTE'
AS
  CALL set_return_value_sp();

-- Create a task that calls the get_return_value stored procedure.
CREATE TASK get_return_value_t
WAREHOUSE=warehouse1
AFTER set_return_value_t
AS
  CALL get_return_value_sp();

-- Resume task.
-- Wait for task to run on schedule.

SELECT DISTINCT(str) FROM return_values_sp;
+-----------------------------------------------+
|                      STR                      |
+-----------------------------------------------+
|  The quick brown fox jumps over the lazy dog  |
+-----------------------------------------------+

SELECT DISTINCT(RETURN_VALUE)
  FROM TABLE(information_schema.task_history())
  WHERE RETURN_VALUE IS NOT NULL;

+-----------------------------------------------+
|                  RETURN_VALUE                 |
+-----------------------------------------------+
|  The quick brown fox jumps over the lazy dog  |
+-----------------------------------------------+
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示例 3：使用变量来设置返回值

以下示例演示如何根据任务的执行动态生成返回值，并使用变量来设置返回值。在此示例中，任务将数据从流加载到登录表中，并设置返回值，以指示加载的行数：

CREATE OR REPLACE TASK load_raw_data
WAREHOUSE = 'WH'
WHEN
    SYSTEM$STREAM_HAS_DATA('NEW_WEATHER_DATA')
AS
    DECLARE
        rows_loaded NUMBER;
        result_string VARCHAR;
    BEGIN
        INSERT INTO raw_weather_data ( -- our landing table
            row_id)
        SELECT
            row_id
        FROM
            new_weather_data  -- our source stream
        ;

        -- to see the number of rows loaded in the UI
        rows_loaded := (SELECT $1 FROM TABLE(RESULT_SCAN(LAST_QUERY_ID())));
        result_string := :rows_loaded || ' rows loaded into RAW_WEATHER_DATA';
        -- show result string as task return value
        CALL SYSTEM$SET_RETURN_VALUE(:result_string);
    END;
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语言: 中文