Question

SELECT student_id FROM `students` AS s1
WHERE student_id IN 
  (SELECT s2.student_id FROM `students` AS s2
     WHERE s1.year_of_birth = s2.year_of_birth
     LIMIT 10)

无法在我的服务器上处理此查询。它会丢弃错误，表示此版本的mysql不支持子查询内的限制等（ERROR 1235）。

我的mysql 5.1.49版本有什么解决方案吗？

SELECT
    id,
    region
FROM (
    SELECT
        region,
        id,
        @rn := CASE WHEN @prev_region = region
                    THEN @rn + 1
                    ELSE 1
               END AS rn,
        @prev_region := region
    FROM (SELECT @prev_region := NULL) vars, ads T1
    ORDER BY region, id DESC
) T2
WHERE rn <= 4
ORDER BY region, id

感谢 Mark Byers

Answer 1

我想你想要每个生日的十个学生。这是一个最大的每组查询，您可以search Stack Overflow查看如何在MySQL中完成此操作。

如果MySQL支持ROW_NUMBER函数会很容易，但由于它不支持，你可以使用变量来模拟它。例如，为了让每个出生日期有3名学生，您可以这样做：

SELECT
    student_id,
    year_of_birth
FROM (
    SELECT
        year_of_birth,
        student_id,
        @rn := CASE WHEN @prev_year_of_birth = year_of_birth
                    THEN @rn + 1
                    ELSE 1
               END AS rn,
        @prev_year_of_birth := year_of_birth
    FROM (SELECT @prev_year_of_birth := NULL) vars, students T1
    ORDER BY year_of_birth, student_id DESC
) T2
WHERE rn <= 3
ORDER BY year_of_birth, student_id

结果：

测试数据：

CREATE TABLE students (student_id INT NOT NULL, year_of_birth INT NOT NULL);
INSERT INTO students (student_id, year_of_birth) VALUES
(1, 1990),
(2, 1990),
(3, 1991),
(4, 1991),
(5, 1990),
(6, 1992),
(7, 1991),
(8, 1991);

Mysql替代为mysql 5.1.49中子查询内的LIMIT

1 个答案: