Question

我有两个数据表，我使用Inner Join语句查询。其中一个表格提取每日公司股票信息，因此每个公司在市场开放的每一天都有一排。另一个表格包含有关公司的定性数据，每个公司只有一行。

我正在尝试提取最新的股票信息，并将其与HTML表格中的定性公司信息配对。我有一切工作，除了它仍然拉动公司的每一行每日信息而不是最新的。

有人可以协助此查询吗？：

$query = "SELECT daily_info.Day, 
daily_info.Prev_close, 
stocks.Symbol, 
stocks.Company, 
stocks.Description 
FROM daily_info 
INNER JOIN stocks ON daily_info.Symbol = stocks.Symbol 
ORDER BY daily_info.Day, stocks.Company LIMIT 43
"; 

Example: 
Table 1: Daily_info
Day       |  Symbol  |  Company    |  Prev Close
06/15/14  |  CRM     |  Salesforce |  $52.34
06/15/14  |  AMZN    |  Amazon     |  $342.65
06/16/15  |  CRM     |  Salesforce |  $55.24
06/16/14  |  AMZN    |  Amazon     |  $349.64



Table 2: Stock
Symbol  |  Company           | Description
CRM     |  Salesforce.com    | This is a cloud based CRM company
AMZN    |  Amazon.com        | This is an ecommerce company


Output:
Company        |  Symbol   |  Prev Close    |   Description
Amazon.com     |  AMZN     |  $349.64       | This is an ecommerce company 
Salesforce.com |  CRM      |  $55.24        | This is a cloud based CRM company

Answer 1

我不认为MySQL支持LAG功能，所以你需要做一个子查询来获取每个Symbol的最后日期，然后INNER加入该结果。这样的事情应该有效：

 $query = "
    SELECT l.Company, l.Symbol, l.Prev_Close, r2.Description
    FROM Daily_info as l
    INNER JOIN
    (SELECT Symbol, MAX(Prev_close) as last_date FROM Daily_info GROUP BY Symbol) AS r
    ON (l.Symbol=r.Symbol AND l.Prev_close=r.last_date)
    INNER JOIN Stock as r2
    ON (l.Symbol=r2.Symbol)
    ";

MySQL语句拉太多行

1 个答案: