通过自连接从左连接中删除重复的产品

Question

对于 sqlite 我想找到一种方法来删除此结果中的重复项（请参阅 this gist 或 this sqime.org demo）

有些功能适用于所有产品，有些功能仅适用于某些产品。

• 上面的结果返回我想要的——具有所有功能的所有产品，以及德语和英语的功能文本（如果可用）。
• 结果有不正确的行，如第二行

  2024  B12XBE  A1C B1  B1 hardened steal   UT gehärteter Stahl

  两个 feature_text 都应以

  UT

开头

但它包含重复的行。

问题

• 如何最好地避免重复行？
• 如果可能：我想了解底层逻辑（笛卡尔积或类似）。

SQL 演示

这个sql可以作为示例

DROP TABLE IF EXISTS product_features;
DROP TABLE IF EXISTS feature_text;
CREATE TABLE product_features (
    year INTEGER, -- (4) 
    product TEXT, -- (6) 
    feature TEXT -- (3)      
);
CREATE TABLE feature_text (
    year INTEGER, -- (4)    
    product_group TEXT, 
     -- (2) usually matches the first two digits of product 
     -- but is sometimes empty / NULL or blank ' ' 
    feature TEXT, -- (3)
    language INTEGER, -- (2) 
    description1 TEXT -- up to 40
);

插入一些记录

INSERT INTO product_features (year, product, feature) VALUES 
    (2024, 'B12XBE', 'A1C'), (2024, 'B12XBE', '7B0'),
    (2024, 'B12XBE', 'DUL'), (2024, 'UTB2EF', 'A1C'),
    (2024, 'UTB2EF', '7B0'), (2024, 'UTB2EF', 'DUL'),
    (2024, 'X9Y8Z7', 'DUH'), (2024, 'X9Y8Z7', '7B0');
                    
INSERT INTO feature_text
 (year, product_group, feature, language, description1) 
VALUES 
  (2024, 'B1', 'A1C', 1, 'B1 hardened steel'),
  (2024, 'B1', '7B0', 1, 'B1 diamond tip'),
  (2024, 'UT', 'A1C', 1, 'UT hardened steel'),
  (2024, 'UT', '7B0', 1, 'UT diamond tip'),
  (2024, ' ', 'DUL', 1, '10mm for light duty'),
  (2024, 'X9', '7B0', 1, 'X9 diamond tip'),
  (2024, ' ', 'DUH', 1, '13mm for heavy duty'),
  (2024, 'B1', 'A1C', 2, 'B1 gehärteter Stahl'),
  (2024, 'B1', '7B0', 2, 'B1 Diamant Spitze'),
  (2024, 'UT', 'A1C', 2, 'UT gehärteter Stahl'),
  (2024, 'UT', '7B0', 2, 'UT Diamant Spitze'),
  (2024, ' ', 'DUL', 2, '10mm für leichte Aufgaben'),
  (2024, 'X9', '7B0', 2, 'X9 Diamant Spitze'),
  (2024, ' ', 'DUH', 2, '13mm für schwere Aufgaben');

我目前连接表格并将每种语言放在不同列中的方法

WITH prft_en as (
SELECT 
pf.year, pf.product, pf.feature, 
COALESCE(ft1.product_group, ft2.product_group) AS product_group,
COALESCE(ft1.description1, ft2.description1) AS feature_text_en,
COALESCE(ft1.language, ft2.language) AS language_en
  FROM product_features pf
    LEFT JOIN feature_text  ft1
                 ON pf.year = ft1.year 
                 AND pf.feature = ft1.feature
                 AND substr(pf.product, 1,2) = ft1.product_group
    LEFT JOIN feature_text ft2
                 ON pf.year = ft2.year 
                 AND pf.feature = ft2.feature
                 AND ft2.product_group is ' ' OR ft2.product_group is NULL  
WHERE ft1.language = 1 OR ft2.language = 1                 
), prft_de AS (
SELECT 
pf.year, pf.product, pf.feature, 
COALESCE(ft1.product_group, ft2.product_group) AS product_group,
COALESCE(ft1.description1, ft2.description1) AS feature_text_de,
COALESCE(ft1.language, ft2.language) AS language_de
  FROM product_features pf
    LEFT JOIN feature_text  ft1
                 ON pf.year = ft1.year 
                 AND pf.feature = ft1.feature
                 AND substr(pf.product, 1,2) = ft1.product_group
    LEFT JOIN feature_text ft2
                 ON pf.year = ft2.year 
                 AND pf.feature = ft2.feature
                 AND ft2.product_group is ' ' OR ft2.product_group is NULL  
WHERE ft1.language = 2 OR ft2.language = 2
)

对上面创建的 cte 的查询

SELECT prft_en.year, prft_en.product, 
       prft_en.feature, prft_en.product_group, 
       prft_en.feature_text_en, prft_de.feature_text_de 
FROM prft_en 
     LEFT JOIN prft_de
     ON prft_en.year = prft_de.year
     AND prft_en.feature = prft_de.feature
     AND SUBSTR(prft_en.product, 1,2) = prft_en.product_group

Answer 1

我认为整个 CTE 的东西确实不是你想要的。我认为您想要每个产品一行，所以从那开始

SELECT
    f.*,
    substring(f.product, 0, 3) as product_group
from product_features f

然后对于每个产品，您想要获取相应的描述（如果存在），这可以简单地在英语子查询中完成：

    (
        select description1
        from feature_text t
        where f.year = t.year
            and (substring(f.product, 0, 3) = t.product_group or t.product_group = ' ' or t.product_group is null)
            and f.feature = t.feature and language = 1
    ) as feature_text_en,

德语：

    (
        select description1
        from feature_text t
        where f.year = t.year
            and (substring(f.product, 0, 3) = t.product_group or t.product_group = ' ' or t.product_group is null)
            and f.feature = t.feature and language = 2
    ) as feature_text_de

这是 两者都在 sqlime 上 并生成此结果表：

年	产品	特点	产品组	feature_text_en	feature_text_de
2024	B12XBE	A1C	B1	B1硬化偷窃	B1 斯塔尔
2024	B12XBE	7B0	B1	B1钻石尖头	B1 钻石斯皮策
2024	B12XBE	DUL	B1	10mm 适用于轻型	10mm 轻量级
…