Question

我正在将Google Cloud Platform与mySQL一起使用。

我有一个包含3列的表格：

idUser, Name, timestamp
me@you.com, Mike Jones, 1-6-1900 05:00
us@we.com, Steve Brown, 1-2-1900 06:00
jsmith@email.com, John Smith, 1-5-1900 06:00
test@me.com, Sarah Lee, 1-3-1900 05:30

我想基于时间戳作为订单/排序来查询“可以找到jsmith@email.com所在的行号”。

我已经能够部分工作了，我可以根据时间戳生成一些显示行号的结果：

SET @row_number:=0;
SELECT @row_number:=@row_number+1 AS row_number,idUser FROM SpeakerQueueActive
ORDER BY timestamp

这使我得到添加行号的结果：

row_num, idUser, Name, timestamp
1,us@we.com, Steve Brown, 1-2-1900 06:00
2,test@me.com, Sarah Lee, 1-3-1900 05:30
3,jsmith@email.com, John Smith, 1-5-1900 06:00
4,me@you.com, Mike Jones, 1-6-1900 05:00

我想我现在想将其嵌套并使用类似的东西：

SELECT * from
(SET @row_number:=0;
SELECT @row_number:=@row_number+1 AS row_number,idUser FROM SpeakerQueueActive
ORDER BY timestamp)
WHERE idUser = 'jsmith@email.com'

但是我收到一个语法错误的错误消息。我还尝试将第一段代码存储为一个存储过程，然后调用它，但是我似乎也无法将其与SELECT一起使用。

所以回到我的原始问题，我想向我报告他在第3行中

我该怎么做？谢谢！

Answer 1

您需要表名别名FROM ( ) t

SET @row_number:=0;
SELECT t.* from   (
SELECT @row_number:=@row_number+1 AS row_number,idUser FROM SpeakerQueueActive
ORDER BY timestamp) t  /* here add the table name alias */
WHERE t.idUser = 'jsmith@email.com'

Answer 2

SELECT * from
(SET @row_number:=0;
SELECT @row_number:=@row_number+1 AS row_number,idUser FROM SpeakerQueueActive
ORDER BY timestamp)
WHERE idUser = 'jsmith@email.com'

需要将其重写为

SELECT * from (
   SELECT @row_number:=@row_number+1 AS row_number,idUser FROM SpeakerQueueActive
   CROSS JOIN (SELECT @row_number:= 0) AS init
ORDER BY timestamp) AS alias 
WHERE idUser = 'jsmith@email.com'

或作为基于逗号的CROSS JOIN。

SELECT * from (
      SELECT @row_number:=@row_number+1 AS row_number,idUser FROM SpeakerQueueActive
    , (SELECT @row_number:= 0) AS init
ORDER BY timestamp) AS alias 
WHERE idUser = 'jsmith@email.com'

如何在GCP中使用mySQL获取行号并选择特定行？

2 个答案: