SQL 使用 where 条件查询第二大值

Question

我有一个 table，其中包含步骤 ID 和居民 ID。我想编写一个查询来查找特定居民的第二大步骤 ID。

google 示例中使用 max 的查询没有 where 子句。试过这个：

SELECT DISTINCT(step_action_id) 
FROM step_table where resident_id =219 
ORDER BY step_action_id DESC limit 2,1;

Table:

Step_Action_id REsident_id
800               218
801               218
911               218
857               218       
856               219
858               219

我期望的结果是 856。但我收到以下错误，

Error: ILLEGAL USE OF KEYWORD LIMIT.  TOKEN SKIP OPTIMIZE FOR FETCH , EXCEPT MINUS UNION <END-OF-STATEMENT> WAS EXPECTED. SQLCODE=-199, SQLSTATE=42601, DRIVER=3.59.81
SQLState:  42601
ErrorCode: -199
Error: THE CURSOR SQL_CURLH200C1 IS NOT IN A PREPARED STATE. SQLCODE=-514, SQLSTATE=26501, DRIVER=3.59.81
SQLState:  26501
ErrorCode: -

Answer 1

您可以使用 ROW_NUMBER():

SELECT step_action_id
FROM (
  SELECT step_action_id, ROW_NUMBER() OVER(ORDER BY step_action_id DESC) AS rn
  FROM (SELECT DISTINCT step_action_id
        FROM step_table 
        WHERE resident_id = 219
     ) AS s
) AS s2
WHERE rn = 2;

LiveDemo

Answer 2

ROW_NUMBER() 工作得很好，但您还应该知道 DB2 使用 "FETCH FIRST" 而不是限制 "restrict" 返回的行数。所以你可以用子查询得到 2，然后颠倒顺序得到第二个。像这样：

SELECT step_action_id 
FROM (
  SELECT DISTINCT step_action_id 
  FROM step_table 
  WHERE resident_id =219 
  ORDER BY step_action_id DESC
  FETCH FIRST 2 ROWS ONLY
)
ORDER BY step_action_id ASC
FETCH FIRST 1 ROWS ONLY

Answer 3

如果步骤 ID 不同，您可以只使用 OFFSET 和 FIRST FIRST 1 ROW ONLY:

SELECT step_action_id
FROM step_table 
WHERE resident_id = 219 
ORDER BY step_action_id DESC
OFFSET 1 ROWS
FETCH FIRST 1 ROW ONLY;

如果它们不明显，只需添加一个GROUP BY或SELECT DISTINCT：

SELECT step_action_id
FROM step_table 
WHERE resident_id = 219 
GROUP BY step_action_id
ORDER BY step_action_id DESC
OFFSET 1 ROWS
FETCH FIRST 1 ROW ONLY;

Answer 4

谢谢大家让我知道解决这个问题的各种方法。我使用以下查询解决了问题

SELECT max(step_action_id) FROM step_table as p WHERE p.step_action_id < (SELECT max(t.step_action_id) FROM step_table 作为 t 其中 t.residentId = 219) 和 p.residentId = 219";

SQL 使用 where 条件查询第二大值

SQL query for second largest value with a where condition

sql

db2

greatest-n-per-group