sql - 从一个类型中只获取一行

Question

我有一张桌子票和另一张桌子日志。ticket中的每一行都有很多日志。我想知道某个字符串是否在某个日志中，然后从票证中获取一个寄存器，无论哪个都没有关系，因为我只想每张票获得一行。这是我目前所拥有的：

SELECT ticket.id,ticket.description,ticket.owner 
FROM ticket
JOIN log
ON (log.ticketid=ticket.id)
where log.description LIKE '%someparameter%'

在这种情况下我该怎么办？

Answer 1

您可以尝试使用 SQL 限制选项吗？

SELECT ticket.id,ticket.description,ticket.owner 
FROM ticket
JOIN log
ON (log.ticketid=ticket.id)
where log.description LIKE '%someparameter%'
LIMIT 1;

Answer 2

SELECT
  *
FROM
  ticket
WHERE
  EXISTS (SELECT *
            FROM log
           WHERE log.ticketid = ticket.id
             AND log.description LIKE '%someparameter%'

或者...

SELECT
  ticket.id, ticket.description, ticket.owner 
FROM
  ticket
INNER JOIN
  log
    ON (log.ticketid=ticket.id)
WHERE
  log.description LIKE '%someparameter%'
GROUP BY
  ticket.id, ticket.description, ticket.owner 

Answer 3

通常的 DB2 等价于 LIMIT 1 是 FETCH FIRST 1 ROWS ONLY：

SELECT ticket.id,ticket.description,ticket.owner 
FROM ticket
JOIN log
ON (log.ticketid=ticket.id)
where log.description LIKE '%someparameter%'
FETCH FIRST 1 ROWS ONLY

您还可以通过以下方式启用 LIMIT 语法：

db2set DB2_COMPATIBILITY_VECTOR=4000

或者：

db2set DB2_COMPATIBILITY_VECTOR=MYS