在SQL中如何遍历where子句中的值列表

Question

我有一个名为“titles”的表，它具有以下值：

id   title  time
1    ABC    1-1-2021
2    EEE    1-1-2021
3    ABC    1-1-2020
4    123    2-1-2020

现在我想从这个表中选择带有给定列表的记录，例如：

let title_to_search = [ABC, 123]

按 DESC 中的“时间”列排序

我想在搜索表“标题”后得到以下结果：

id   title  time
1    ABC    1-1-2021
4    123    2-1-2020

我尝试过以下状态：

select * from titles where title in title_to_search order by time DESC

结果是

id   title  time
1    ABC    1-1-2021
3    ABC    1-1-2020
4    123    2-1-2020

这是由 id "3" 也有 title 值 "ABC" 引起的。但是，我想要的是遍历列表，这意味着如果“ABC”已在where子句中使用，则不应再次使用，因此应选择记录“1”，不应选择“3” , 应该选择 4。

这样的SQL语句怎么写？

我正在使用 MySQL 数据库。

Answer 1

我认为你需要这样的东西

SELECT a.*
FROM titles a
WHERE a.title IN ( 'ABC', '123' )
AND NOT EXISTS (
 SELECT 1
 FROM titles b
 WHERE b.title = a.title
 AND b.id < a.id
)

b.id < a.id 可以根据您的要求更改，可能是time？

关于性能

mysql> SELECT COUNT(*) FROM titles a WHERE a.title IN ( 'A2617', 'A6983' );
+----------+
| COUNT(*) |
+----------+
|       33 |
+----------+
1 row in set (0.00 sec)

mysql> select count(*) from titles;
+----------+
| count(*) |
+----------+
|   707280 |
+----------+
1 row in set (0.03 sec)

mysql> EXPLAIN SELECT a.* FROM titles a WHERE a.title IN ( 'A2617', 'A6983' ) AND NOT EXISTS (  SELECT 1  FROM titles b  WHERE b.title = a.title  AND b.id < a.id );
+----+-------------+-------+------------+-------+---------------+-------+---------+--------------+------+----------+--------------------------------------+
| id | select_type | table | partitions | type  | possible_keys | key   | key_len | ref          | rows | filtered | Extra                                |
+----+-------------+-------+------------+-------+---------------+-------+---------+--------------+------+----------+--------------------------------------+
|  1 | SIMPLE      | a     | NULL       | range | _Idx1         | _Idx1 | 32      | NULL         |   33 |   100.00 | Using index condition                |
|  1 | SIMPLE      | b     | NULL       | ref   | PRIMARY,_Idx1 | _Idx1 | 32      | test.a.title |    1 |   100.00 | Using where; Not exists; Using index |
+----+-------------+-------+------------+-------+---------------+-------+---------+--------------+------+----------+--------------------------------------+
2 rows in set, 3 warnings (0.00 sec)

mysql> SELECT a.* FROM titles a WHERE a.title IN ( 'A2617', 'A6983' ) AND NOT EXISTS (  SELECT 1  FROM titles b  WHERE b.title = a.title  AND b.id < a.id );
+--------+-------+------------+
| id     | title | time       |
+--------+-------+------------+
| 404071 | A2617 | 2021-12-14 |
| 397458 | A6983 | 2021-12-14 |
+--------+-------+------------+
2 rows in set (0.01 sec)

mysql> SELECT a.* FROM titles a WHERE a.title IN ( 'A2617', 'A6983' );
+--------+-------+------------+
| id     | title | time       |
+--------+-------+------------+
| 404071 | A2617 | 2021-12-14 |
| 495677 | A2617 | 2021-12-14 |
| 505974 | A2617 | 2021-12-14 |
| 522148 | A2617 | 2021-12-14 |
| 523088 | A2617 | 2021-12-14 |
| 545776 | A2617 | 2021-12-14 |
| 546174 | A2617 | 2021-12-14 |
| 565224 | A2617 | 2021-12-14 |
| 594082 | A2617 | 2021-12-14 |
| 634224 | A2617 | 2021-12-14 |
| 663641 | A2617 | 2021-12-14 |
| 684980 | A2617 | 2021-12-14 |
| 727136 | A2617 | 2021-12-14 |
| 733046 | A2617 | 2021-12-14 |
| 738378 | A2617 | 2021-12-14 |
| 747396 | A2617 | 2021-12-14 |
| 397458 | A6983 | 2021-12-14 |
| 398483 | A6983 | 2021-12-14 |
| 416826 | A6983 | 2021-12-14 |
| 418081 | A6983 | 2021-12-14 |
| 426902 | A6983 | 2021-12-14 |
| 454826 | A6983 | 2021-12-14 |
| 479057 | A6983 | 2021-12-14 |
| 486494 | A6983 | 2021-12-14 |
| 492336 | A6983 | 2021-12-14 |
| 515798 | A6983 | 2021-12-14 |
| 570730 | A6983 | 2021-12-14 |
| 587073 | A6983 | 2021-12-14 |
| 627372 | A6983 | 2021-12-14 |
| 672636 | A6983 | 2021-12-14 |
| 699460 | A6983 | 2021-12-14 |
| 722743 | A6983 | 2021-12-14 |
| 747387 | A6983 | 2021-12-14 |
+--------+-------+------------+
33 rows in set (0.00 sec)

Answer 2

以下将适用于示例数据以及所有额外数据：

从 id 所在的标题中选择 * (SELECT MIN(ID) FROM TITLES WHERE TITLE IN TITLE_TO_SEARCH GROUP BY TITLE)