Question

或者至少我认为它们被称为子查询（新手和SQLite中的自我训练）。我在同一个数据库中的两个表中有两个SELECT语句。我想在列date和symbol上加入这两个子查询。子查询可以单独运行，但是当我尝试JOIN时出现错误（error in statement: near "JOIN": syntax error）。这是我的查询字符串：

SELECT date, symbol, SUM(oi*contract_settle) AS oi_dollar
    FROM (SELECT date, symbol, oi, contract_settle
            FROM ann
            UNION
            SELECT date, symbol, oi, contract_settle
            FROM qtr) 
    GROUP BY date, symbol
    HAVING oi_dollar > 0
    JOIN
    (SELECT date, symbol, ret FROM crsp
    USING (date, symbol))

谢谢！

Answer 1

您的JOIN子句需要在GROUP BY子句之前。此外，我知道sqlite确实有一些不同的“可选”连接语法，但以下更标准的查询应该有效：

SELECT a.date, a.symbol, SUM(a.oi * a.contract_settle) AS oi_dollar
FROM (SELECT date, symbol, oi, contract_settle
        FROM ann
        UNION
        SELECT date, symbol, oi, contract_settle
        FROM qtr) a
INNER JOIN crsp c ON a.date = c.date AND a.symbol = c.symbol
WHERE a.oi * a.contract_settle > 0
GROUP BY a.date, a.symbol

如果您对oi和contract_settle列有更多了解（例如，它们永远不会都是负数），a.oi <> 0 AND a.contract_settle <> 0的WHERE子句可能会有更好的性能。

Answer 2

您需要通过on子句定义联接方式。我不知道SQLite，但在SQL中，它会像这样（可能不会运行）：

SELECT date, symbol, SUM(oi*contract_settle) AS oi_dollar
    FROM (SELECT date, symbol, oi, contract_settle
            FROM ann
            UNION
            SELECT date, symbol, oi, contract_settle
            FROM qtr) as 'a'
    JOIN
    (SELECT date, symbol, ret FROM crsp
    USING (date, symbol)) as 'b'
    ON a.date = b.date AND a.symbol = b.symbol
    GROUP BY date, symbol
    HAVING oi_dollar > 0

SQLite - 加入两个子查询

2 个答案: