[英]Can SQL sort on the significant part of a number?
我有一列国家拨号代码我希望将前缀过滤到最左边的拨号代码中
这是源列:
prefix
------
542
54299
374
37477
37493
37494
37498
37447
37455
3749
37410
297
29756
29759
29766
29769
29796
29799
29773
29774
297600
297622
247
61
61861
61862
61863
这是我想要的结果的一个例子。 sql可以轻松地做到这一点,以及如何或有更好的方法。 请记住,将有大约30k行
significant prefix
----------------------
542 542
542 54299
374 374
374 37477
374 37493
374 37494
374 37498
374 37447
374 37455
374 3749
374 37410
297 297
297 29756
297 29759
297 29766
297 29769
297 29796
297 29799
297 29773
297 29774
297 297600
297 297622
247 247
61 61
61 61861
61 61862
61 61863
您可能想尝试以下(使用MySQL的INSTR()
和LENGTH()
函数):
SELECT ( SELECT prefix
FROM numbers n2
WHERE INSTR(n1.prefix, n2.prefix) = 1
ORDER BY LENGTH(n2.prefix)
LIMIT 1
) AS significant,
n1.prefix
FROM numbers n1;
查看@ onedaywhen的上述查询的ANSI SQL版本的答案 。
测试用例:
CREATE TABLE numbers (prefix int);
INSERT INTO numbers VALUES (542);
INSERT INTO numbers VALUES (54299);
INSERT INTO numbers VALUES (374);
INSERT INTO numbers VALUES (37477);
INSERT INTO numbers VALUES (37493);
INSERT INTO numbers VALUES (37494);
INSERT INTO numbers VALUES (37498);
INSERT INTO numbers VALUES (37447);
INSERT INTO numbers VALUES (37455);
INSERT INTO numbers VALUES (3749);
INSERT INTO numbers VALUES (37410);
INSERT INTO numbers VALUES (297);
INSERT INTO numbers VALUES (29756);
INSERT INTO numbers VALUES (29759);
INSERT INTO numbers VALUES (29766);
INSERT INTO numbers VALUES (29769);
INSERT INTO numbers VALUES (29796);
INSERT INTO numbers VALUES (29799);
INSERT INTO numbers VALUES (29773);
INSERT INTO numbers VALUES (29774);
INSERT INTO numbers VALUES (297600);
INSERT INTO numbers VALUES (297622);
INSERT INTO numbers VALUES (247);
INSERT INTO numbers VALUES (61);
INSERT INTO numbers VALUES (61861);
INSERT INTO numbers VALUES (61862);
INSERT INTO numbers VALUES (61863);
结果:
+-------------+--------+
| significant | prefix |
+-------------+--------+
| 542 | 542 |
| 542 | 54299 |
| 374 | 374 |
| 374 | 37477 |
| 374 | 37493 |
| 374 | 37494 |
| 374 | 37498 |
| 374 | 37447 |
| 374 | 37455 |
| 374 | 3749 |
| 374 | 37410 |
| 297 | 297 |
| 297 | 29756 |
| 297 | 29759 |
| 297 | 29766 |
| 297 | 29769 |
| 297 | 29796 |
| 297 | 29799 |
| 297 | 29773 |
| 297 | 29774 |
| 297 | 297600 |
| 297 | 297622 |
| 247 | 247 |
| 61 | 61 |
| 61 | 61861 |
| 61 | 61862 |
| 61 | 61863 |
+-------------+--------+
27 rows in set (0.00 sec)
即使您使用varchar
存储数字,它也应该工作。
更新:
至于性能,您可能需要考虑缓存表中的significant
部分:
CREATE TABLE numbers (prefix int, significant int);
-- Fill in the prefixes, leaving the significant field as NULL.
然后你可以生成如下significant
字段(使用MySQL):
UPDATE numbers n
JOIN ( SELECT ( SELECT prefix
FROM numbers n2
WHERE INSTR(n1.prefix, n2.prefix) = 1
ORDER BY LENGTH(n2.prefix)
LIMIT 1
) AS significant,
n1.prefix
FROM numbers n1
) s ON (s.prefix = n.prefix)
SET n.significant = s.significant;
SELECT * FROM numbers;
+--------+-------------+
| prefix | significant |
+--------+-------------+
| 542 | 542 |
| 54299 | 542 |
| 374 | 374 |
| 37477 | 374 |
| 37493 | 374 |
| 37494 | 374 |
...
每当在numbers
表中添加新行时,您可能希望运行UPDATE
查询。
这个问题只有一个'sql'标签(没有'MySQL'标签)所以这里是一个使用标准SQL的建议解决方案,假设prefix
是名为Numbers
的表中的INTEGER
列:
SELECT (
SELECT MIN(N2.prefix)
FROM Numbers AS N2
WHERE CAST(N1.prefix AS VARCHAR) LIKE CAST(N2.prefix AS VARCHAR) + '%'
) AS significant,
N1.prefix
FROM Numbers AS N1;
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