sql - PostgreSQL 查询中的条件语句

Question

我这里有 3 个表:

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      |

我只想显示满足这些条件的每个人的电话号码:

• 如果他有一个“家庭”电话类型号码，则只显示家庭类型，删除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“手机”号码，然后放弃所有其他(“传真”、“主”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 然后我从这里分离了所有的电话类型号码，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';

然后创建另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;

满足我条件的步骤对吗？ 我仍然从一个人那里得到不同的电话类型值。

Answer 1

您费了很大的劲才得到这个查询能给您的信息:

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，我都使用它来获得您似乎在单个查询级别中寻找的排序顺序。

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

我在排名 (r.rnk) 信息后附加了一个 VALUES expression使其与您提供的表格布局一起使用。不过，更好的是，您可以将 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;

然后您的查询变得更简单:

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)