[英]SQL for setting column value same as next row's column value
我有这样的桌子
--------------------------
id some_column
--------------------------
1 null
2 abc
3 null
4 null
5 def
6 ghi
在我的场景中,表中的某些初始行在some_column中为null。 所有最新的行均已正确设置some_column值 。
我想运行一个查询,该查询可以通过从下一个非null值复制值来替换some_column的所有null值。
例如,运行查询后,表将变为
--------------------------
id some_column
--------------------------
1 abc
2 abc
3 def
4 def
5 def
6 ghi
我正在尝试这样的事情
update table as t1 set some_column = (select some_column from table as t2 where t2.id > t1.id and t2.some_column is not null limit 1) where some_column is null
但出现错误
You can't specify target table 't1' for update in FROM clause
您可以使用JOIN
来做到这一点:
UPDATE t AS t0
JOIN (
SELECT t1.id, MIN(t2.id) new_id
FROM t AS t1
JOIN t AS t2 ON t1.id < t2.id
WHERE t1.some_column IS NULL
AND t2.some_column IS NOT NULL
GROUP BY t1.id) AS tnew ON t0.id = tnew.id
JOIN t AS t3 ON t3.id = tnew.new_id
SET t0.some_column = t3.some_column
tnew
子查询将具有空值的每个ID与具有非空值的下一个最高ID匹配。 然后,我将其与原始表连接两次,以将要更新的行与该行的值与替换值配对。
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