Question

我这里有3张表：

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表格中存储多个号码，并且phonetype表格中的语音种类不同：

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

我只想显示符合以下条件的每个人的电话号码：

如果他有一个'Home'语音类型号码显示，只有家庭类型会丢弃所有其他的音位类型号码。
如果他没有'Home'号码，那么只显示他的'Cell'号码然后丢弃所有其他号码（'Fax'，'Main'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fullname, number, phonetype的{{1}}，然后从这里我将所有的类型数字分开，如：

testable

然后创建另一组临时表，我认为满足上述条件：

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';

最后选择最后一组临时表的所有联合：

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);

满足我条件的步骤是否正确？我仍然从一个人那里获得不同的语音值。

Answer 1

为了获得这个单一查询可以提供的内容，您遇到了很多麻烦：

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?

我使用VALUES expression添加了排名（r.rnk）信息，以使其与您呈现的表格布局配合使用。但是，更好的是，您永久地添加到表phonetype：

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)

PostgreSQL查询中的条件语句

1 个答案: