如何在 VIEW 的内部 SELECT 查询中将 WHERE 约束传递给 count(...) 函数？

Question

我在 SQLite 中有一个 VIEW，示意性地如下所示：

SELECT ownerid, field, origin, count FROM (
    SELECT 
        null AS ownerid,
        table1.somefield AS field,
        0 AS origin,
        count(table2.ownerid) AS count
    FROM table1 LEFT JOIN table2
    UNION ALL
    SELECT 
        table2.ownerid AS ownerid,
        table2.someotherfield AS field,
        1 AS origin,
        1 AS count
)

我用SELECT FROM viewname WHERE ownerid=? OR origin=0 类型的查询来调用它——换句话说，我想要的是第一个表中的条目，加上所有者ID 正确的第二个表中的条目。

第一个表的计数列应该是第二个表中与约束匹配的所有行的计数 - 换句话说，其 ownerid 是为其选择的行。我目前得到的是整个表的计数。

如何约束 count(...) 函数调用中的表达式以匹配传递给 VIEW 的查询约束？

Answer 1

count(SELECT * FROM table2 WHERE ownerid=?)

我认为你真正需要的是简化你的视图并限制信息。

SELECT ownerid, field, origin, count FROM (
    SELECT 
        null AS ownerid,
        table1.somefield AS field,
        0 AS origin
    FROM table1 LEFT JOIN table2
    UNION ALL
    SELECT 
        table2.ownerid AS ownerid,
        table2.someotherfield AS field,
        1 AS origin
)

然后像这样从中获取所需的计数等

SELECT *, CASE WHEN viewname.ownerid IS NULL THEN COUNT(select * from table2 where ownerid=?) ELSE 1 END
FROM viewname