如何在where子句中将两个不同的sql查询组合成一个主键

Question

我必须在 Postgres 中执行一个函数，该函数需要从同一个表返回两个不同查询的结果，并在同一个表字段（即主键）上使用 where 子句。

具有相同索引号（又名 inIndex、outIndex）的那些是相关的，其中一个是输入，第二个是它的输出。

例子：

SELECT 
       '9' as inIndex, 
       name as inFieldName 
    from FIELDS 
    where field_id = 1000000005

UNION

SELECT 
       '10' as inIndex, 
       name as inFieldName 
    from FIELDS 
    where field_id = 1000000007;

SELECT  
       '9' as outIndex, 
       name as outFieldName 
    from FIELDS 
    where field_id = 1000000004

UNION 

SELECT  
       '10' as outIndex, 
       name as outFieldName 
    from FIELDS 
    where field_id = 1000000006;

有没有办法将两个查询合二为一？

如果不是，如何将两个查询结果返回到 pl/pgsql 函数中的一个结果集中？

到目前为止，我已经提出了两个循环，将结果添加到具有 3 列（索引、inFiled、outField）的自定义类型中。有没有更好的方法来处理这个过程？

Answer 1

这样的事情怎么样：

SELECT
    '9' AS FieldIndex,
    InFields.name AS InFieldName,
    OutFields.name AS OutFieldName
FROM
    FIELDS AS InFields,
    FIELDS AS OutFields
WHERE
    InFields.field_id = 1000000005
AND OutFields.field_id = 1000000004

UNION

SELECT
    '10' AS FieldIndex,
    InFields.name AS InFieldName,
    OutFields.name AS OutFieldName
FROM
    FIELDS AS InFields,
    FIELDS AS OutFields
WHERE
    InFields.field_id = 1000000007
AND OutFields.field_id = 1000000006

显然你可能需要稍微调整一下...