Question

我正在研究一些遗留SQL（用sybase术语编写）并将其转换为SQL-92兼容形式。问题是，我无法理解“* =”的行为。

查询（适当审查）：

SELECT 
    C.*, SUM(P.qty) from Cars C, Parts P
WHERE 
    C.carid = 1
AND C.carid *= P.carid
AND C.missingpart *= P.missingpart
AND C.manufacturer *= P.manufacturer
AND P.qty is not null
GROUP BY C.carid, C.missingpart, C.manufacturer

我将其转换为：

SELECT
    C.*, SUM(P.qty) from Cars C
        LEFT JOIN Parts P
        ON C.carid = P.carid
        AND C.missingpart = P.missingpart
        AND C.manufacturer = P.manufacturer
WHERE
    C.carid = 1
AND P.qty is not null
GROUP BY C.carid, C.missingpart, C.manufacturer

但事实证明 - 它们并不等同。有人可以帮我理解sybase外连接中“* =”的确切行为以及为什么我的两个查询不相同？

谢谢：）

PS：我正在使用Sybase ASE TDS 5.5

Answer 1

尝试将AND P.qty is not null从WHERE子句移动到连接表达式。

Sybase外连接行为

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