MS SQL 到 SQLite 语法

Question

首先，我正在努力实现以下目标：

我首先使用 MS SQL 来确定如何将标签对齐在一起。

如果您想重新创建未规范化的表，这里是架构。

CREATE TABLE unnormalized(
  vendor_tag varchar(200),
  vendor_tag_name varchar(200),
  vendor_id int
  );
  
 INSERT INTO unnormalized
VALUES
('5,8,30,24','Burgers,Desserts,Fries,Salads',1),
('5','Burgers',2),
('8,42','Desserts,Mexican',3),
('1,5,30,16','American,Burgers,Fries,Sandwiches',4),
('1,5,30,16','American,Burgers,Fries,Sandwiches',5);

这是规范化表的代码

SELECT
    --*
    DISTINCT CAST(tag_id AS INT) as tag_id ,tag_name
FROM unnormalized 
CROSS APPLY 
(
    (SELECT 
        value as tag_id,
        ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) AS rn
     FROM STRING_SPLIT(vendor_tag,',') 
    ) a1
    INNER JOIN 
    (SELECT 
        value as tag_name,
        ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) AS rn
     FROM STRING_SPLIT(vendor_tag_name,',') 
     ) a2
    ON a1.rn = a2.rn
) 
ORDER BY tag_id

现在我正在尝试使用 SQLite 重写此代码。但是，SQLite 中没有一些差异，例如“CROSS APPLY”和“STRING_SPLIT”。我环顾四周，发现 CROSS APPLY 可能类似于 SQLite 中的“CROSS JOIN”，并且可能使用类似这样的东西在它找到的第一个逗号处分隔字符串？？

WITH split(vendor_id, vendor_tag, str) AS (
    SELECT vendor_id, '', vendor_tag||',' FROM unnormalized
    UNION ALL SELECT vendor_id,
    substr(str, 0, instr(str, ',')),
    substr(str, instr(str, ',')+1)
    FROM split 
    WHERE str
) 

SELECT vendor_id, vendor_tag
FROM split 
WHERE vendor_tag
ORDER BY vendor_id;

Answer 1

在 SQLite 中，您可以使用递归 CTE：

WITH cte AS (
  SELECT 
    vendor_tag, 
    vendor_tag_name,
    SUBSTR(vendor_tag, 1, INSTR(vendor_tag || ',', ',') - 1) col1,
    SUBSTR(vendor_tag_name, 1, INSTR(vendor_tag_name || ',', ',') - 1) col2
  FROM unnormalized 
  UNION ALL 
  SELECT 
    SUBSTR(vendor_tag, LENGTH(col1) + 2), 
    SUBSTR(vendor_tag_name, LENGTH(col2) + 2), 
    SUBSTR(SUBSTR(vendor_tag, LENGTH(col1) + 2), 1, INSTR(SUBSTR(vendor_tag, LENGTH(col1) + 2) || ',', ',') - 1),
    SUBSTR(SUBSTR(vendor_tag_name, LENGTH(col2) + 2), 1, INSTR(SUBSTR(vendor_tag_name, LENGTH(col2) + 2) || ',', ',') - 1)
  FROM cte  
  WHERE LENGTH(vendor_tag) AND LENGTH(vendor_tag_name)
)
SELECT DISTINCT col1 vendor_tag, col2 vendor_tag_name
FROM cte
WHERE NOT (INSTR(col1, ',') OR INSTR(col2, ',')) AND (LENGTH(col1) AND LENGTH(col2))
ORDER BY vendor_tag + 0

请参阅demo。
结果：

> vendor_tag | vendor_tag_name
> :--------- | :--------------
> 1          | American       
> 5          | Burgers        
> 8          | Desserts       
> 16         | Sandwiches     
> 24         | Salads         
> 30         | Fries          
> 42         | Mexican