Question

我有一个sqlite3数据库，其中每一行都有自动递增的id和一些可以是NULL的值。我需要删除带有空值的尾部（理想情况下，保留此段中最旧的空记录）。例如，在这里，我想删除 id = 12..16 （或理想情况下为13..16）的行。

任何想法如何在sqlite中完成？

CREATE TABLE tail (id INTEGER PRIMARY KEY, val TEXT);
INSERT INTO "tail" VALUES(1,'5');
INSERT INTO "tail" VALUES(2,'7');
INSERT INTO "tail" VALUES(3,'100');
INSERT INTO "tail" VALUES(4,'150');
INSERT INTO "tail" VALUES(5,NULL);
INSERT INTO "tail" VALUES(6,NULL);
INSERT INTO "tail" VALUES(7,'120');
INSERT INTO "tail" VALUES(8,'150');
INSERT INTO "tail" VALUES(9,'152');
INSERT INTO "tail" VALUES(10,NULL);
INSERT INTO "tail" VALUES(11,'152');
INSERT INTO "tail" VALUES(12,NULL);
INSERT INTO "tail" VALUES(13,NULL);
INSERT INTO "tail" VALUES(14,NULL);
INSERT INTO "tail" VALUES(15,NULL);
INSERT INTO "tail" VALUES(16,NULL);

我可以通过两个步骤轻松完成，例如：

to_delete = []
for row in query("SELECT * FROM tail ORDER BY -id"):
    if row.id IS NOT NONE:
        break
    to_delete.add(row.id)
# optionally: to_delete.remove_last()
query("DELETE FROM tail WHERE id IN (?)", to_delete)

但这不是在事务中，我觉得有一些巧妙的技巧可以用来在单个sqlite语句中实现这一点。

Answer 1

您可以使用：

delete from tail
    where id > (select max(t2.id) from tail t2 where t2.val is not null) and
          val is null and
          id <> (select max(t3.id) from tail t3 where t3.val is null);

如何在sqlite中选择带有空值的尾部？

1 个答案: