Teradata第一个和最后一个值

如何在特殊列上获取group by列的第一个值和最后一个值？ 例如：我需要基于group by og case id的case_owner列的first_值和last_值。

第一个值：

select case_owner  as case_owner_first_value
from
table
qualify row_number() over (partition by case_id  order by case_id) = 1

对于最后一个值：

select case_owner  as case_owner_last_value
from
table
qualify row_number() over (partition by case_id order by case_id desc ) = 1

对于第一个值：

select case_owner  as case_owner_first_value
from
table
qualify row_number() over (partition by case_id  order by case_id) = 1

对于最后一个值：

select case_owner  as case_owner_last_value
from
table
qualify row_number() over (partition by case_id order by case_id desc ) = 1

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请注意，在将第一个_值与ORDERBY子句组合时，可能需要在它们之间添加行

例如：

CREATE VOLATILE TABLE test_fv (id INTEGER,seq SMALLINT) ON COMMIT PRESERVE ROWS;

INSERT INTO test_fv VALUES (NULL,1);
INSERT INTO test_fv VALUES (2,2);
INSERT INTO test_fv VALUES (3,3);
INSERT INTO test_fv VALUES (4,4);
INSERT INTO test_fv VALUES (5,5);

SELECT seq, FIRST_VALUE(id ignore NULLS) OVER (ORDER BY seq ASC ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) FROM test_fv;

这行不通：

SELECT seq, FIRST_VALUE(id ignore NULLS) OVER (ORDER BY seq ASC) FROM test_fv;

---

请注意，在将第一个_值与ORDERBY子句组合时，可能需要在它们之间添加行

例如：

CREATE VOLATILE TABLE test_fv (id INTEGER,seq SMALLINT) ON COMMIT PRESERVE ROWS;

INSERT INTO test_fv VALUES (NULL,1);
INSERT INTO test_fv VALUES (2,2);
INSERT INTO test_fv VALUES (3,3);
INSERT INTO test_fv VALUES (4,4);
INSERT INTO test_fv VALUES (5,5);

SELECT seq, FIRST_VALUE(id ignore NULLS) OVER (ORDER BY seq ASC ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) FROM test_fv;

这行不通：

SELECT seq, FIRST_VALUE(id ignore NULLS) OVER (ORDER BY seq ASC) FROM test_fv;

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请参见：您可以使用windows agg函数，如row_number（）或rank（）。请参见：您可以使用windows agg函数，如row_number（）或rank（）。