PostgreSQL 查询中的条件语句

Question

我这里有 3 个表，即：

person (
  id int PRIMARY KEY
 ,fullname text)

phonenumber (
  id int PRIMARY KEY
 ,personid int REFERENCES person(id)
 ,phonetypeid REFERENCES phonetype(id)
 ,number text)

phonetype (
 id int PRIMARY KEY
,phonetype text) -- phonetype  'Home', 'Cell', 'Fax', 'Main' etc.

每个person 可以在phonenumber 表中存储多个号码，并在phonetype 表中具有不同的电话类型：

| fullname         | number        | phonetype |
| Erwin Macale     | (671)632-3909 | Home      |
| Erwin Macale     | (671)632-3909 | Cell      |
| Erwin Macale     | (671)632-3909 | Main      |

我只想在以下条件下显示每个人的电话号码：

• 如果他有“家庭”电话类型号码，则仅显示家庭类型删除他所有其他电话类型号码。
• 如果他没有“家庭”号码，则只显示他的“小区”号码，然后删除他所有的其他（“传真”、“主要”等）号码。
• 一个人可以没有电话号码。

我创建了一个临时表，其中包含名为 testable 的 fullname, number, phonetype，然后我从这里分隔了所有电话类型号码，例如：

CREATE TEMP TABLE home AS SELECT * FROM testable WHERE phonetype ILIKE 'home';
CREATE TEMP TABLE cell AS SELECT * FROM testable WHERE phonetype ilike 'cell';
CREATE TEMP TABLE main AS SELECT * FROM testable WHERE phonetype ilike 'main';
CREATE TEMP TABLE fax AS SELECT * FROM testable WHERE phonetype ilike 'fax';
CREATE TEMP TABLE work AS SELECT * FROM testable WHERE phonetype ilike 'work';
CREATE TEMP TABLE neighbor AS SELECT * FROM testable WHERE phonetype ilike 'neighbor';
CREATE TEMP TABLE other AS SELECT * FROM testable WHERE phonetype ilike 'other';
CREATE TEMP TABLE unknown AS SELECT * FROM testable WHERE phonetype ilike 'unknown';

然后再创建一组我认为满足上述条件的临时表：

CREATE TEMP TABLE all_cell AS SELECT * FROM cell EXCEPT SELECT * FROM home;
CREATE TEMP TABLE all_main AS (SELECT * FROM main) EXCEPT (SELECT * FROM home UNION SELECT * FROM cell);
CREATE TEMP TABLE all_fax AS (SELECT * FROM fax) EXCEPT (SELECT * FROM home UNION SELECT * FROM cell UNION SELECT * FROM main);
CREATE TEMP TABLE all_work AS (SELECT * FROM work) EXCEPT (SELECT * FROM home UNION SELECT * FROM cell UNION SELECT * FROM main UNION SELECT * FROM fax);
CREATE TEMP TABLE all_neighbor AS (SELECT * FROM neighbor) EXCEPT (SELECT * FROM home UNION SELECT * FROM cell UNION SELECT * FROM main UNION SELECT * FROM fax UNION SELECT * FROM work);
CREATE TEMP TABLE all_other AS (SELECT * FROM other) EXCEPT (SELECT * FROM home UNION SELECT * FROM cell UNION SELECT * FROM main UNION SELECT * FROM fax UNION SELECT * FROM work UNION SELECT * FROM neighbor);
CREATE TEMP TABLE all_unknown AS (SELECT * FROM unknown) EXCEPT (SELECT * FROM home UNION SELECT * FROM cell UNION SELECT * FROM main UNION SELECT * FROM fax UNION SELECT * FROM work UNION SELECT * FROM neighbor UNION SELECT * FROM other);

最后选择最后一组临时表的所有并集：

SELECT fullname, number, phonetype FROM (
    SELECT * FROM home
    UNION 
    SELECT * FROM all_cell
    UNION 
    SELECT * FROM all_main
    UNION 
    SELECT * FROM all_fax
    UNION 
    SELECT * FROM all_work
    UNION 
    SELECT * FROM all_neighbor
    UNION 
    SELECT * FROM all_other
    UNION 
    SELECT * FROM all_unknown
) AS t1
ORDER BY t1.fullname, t1.phonetype;

满足我的条件的步骤正确吗？ 我仍然从一个人那里得到不同的电话类型值。

Answer 1

您费了很多力气才得到这个单一的查询能给您带来什么：

SELECT DISTINCT ON (p.fullname, p.id)
       p.fullname, n.number, t.phonetype
FROM   phonenumber n 
JOIN   person      p ON p.id = n.personid
JOIN   phonetype   t ON t.id = n.phonetypeid
LEFT   JOIN (
   VALUES
     (1, 'home')
    ,(2, 'cell')
    ,(3, 'main')
    ,(4, 'fax')
    ,(5, 'work')
    ,(6, 'neighbor')
    ,(7, 'other')
    ,(8, 'unknown')
   ) r(rnk, phonetype) USING (phonetype)
ORDER  BY p.fullname, p.id, r.rnk;

DISTINCT ON (p.fullname, p.id) 因为fullname 可能不是唯一的。无论如何，我都会使用它来获得您在单个查询级别中寻找的排序顺序。

此相关答案中有关DISTINCT ON的详细信息：
Select first row in each GROUP BY group?

我将排名 (r.rnk) 信息附加到 VALUES expression 以使其适用于您呈现的表格布局。不过，更好的是，您将 phonetype 永久添加到表中：

ALTER TABLE phonetype ADD COLUMN rnk int;

UPDATE phonetype t
SET    rnk = r.rnk
FROM  (
       VALUES
         (1, 'home')
        ,(2, 'cell')
        ,(3, 'main')
        ,(4, 'fax')
        ,(5, 'work')
        ,(6, 'neighbor')
        ,(7, 'other')
        ,(8, 'unknown')
       ) r(rnk, phonetype)
WHERE   r.phonetype = t.phonetype;

然后你的查询变得更简单：

SELECT DISTINCT ON (p.fullname, p.id)
       p.fullname, n.number, t.phonetype
FROM   phonenumber n 
JOIN   person      p ON p.id = n.personid
JOIN   phonetype   t ON t.id = n.phonetypeid
ORDER  BY p.fullname, p.id, t.rnk    -- add more columns to break ties (if any)