技術標籤：mysqlmysql資料庫

Mysql刷題筆記

-- 12.31 如果某列的欄位在該日期為空值，查詢時結果顯示為之前最接近日期的非空值。 

CREATE TABLE T1231
(
	LDate DATE NOT NULL, 
	Value1 INT NULL, 
	Value2 INT NULL
);
INSERT INTO T1231 VALUES('2020-11-25', 500 ,200);
INSERT INTO T1231 VALUES('2020-11-24', Null, 200);
INSERT INTO T1231 VALUES('2020-11-23', Null,
 
 250);
INSERT INTO T1231 VALUES('2020-11-22', 300 ,Null);
INSERT INTO T1231 VALUES('2020-11-21', 200 ,320);

T1231
+------------+--------+--------+
| LDate      | Value1 | Value2 |
+------------+--------+--------+
| 2020-11-25 |    500 |    200 |
| 2020-11-24 |   NULL |    200 |
| 2020-11-23 |   NULL |    250 |
| 2020-11-22
 
 |    300 |   NULL |
| 2020-11-21 |    200 |    320 |
+------------+--------+--------+

結果
+------------+--------+--------+
| LDate      | VALUE1 | VALUE2 |
+------------+--------+--------+
| 2020-11-25 |    500 |    200 |
| 2020-11-24 |    300 |    200 |
| 2020-11-23 |    300 |    250 |
| 2020-11-22 |    300 |    320 |
| 2020-11
 
-21 |    200 |    320 |
+------------+--------+--------+


SELECT A.LDate,
(
  SELECT B.Value1 FROM T1231 B 
  WHERE B.LDate <= A.LDate AND B.Value1 IS NOT NULL 
  ORDER BY A.LDate ASC LIMIT 1
) AS VALUE1,
(
  SELECT B.Value2 FROM T1231 B 
  WHERE B.LDate <= A.LDate AND B.Value2 IS NOT NULL 
  ORDER BY A.LDate ASC LIMIT 1
) AS VALUE2
FROM T1231 A