使用 sqlite 将值拆分为多个部分

Question

我正在努力转换

a | a1,a2,a3
b | b1,b3
c | c2,c1

至：

a | a1
a | a2
a | a3
b | b1
b | b2
c | c2
c | c1

以下是 sql 格式的数据：

CREATE TABLE data(
  "one"  TEXT,
  "many" TEXT
);
INSERT INTO "data" VALUES('a','a1,a2,a3');
INSERT INTO "data" VALUES('b','b1,b3');
INSERT INTO "data" VALUES('c','c2,c1');

解决方案大概是递归的普通Table表达式。

这是一个类似于单行的示例：

WITH RECURSIVE list( element, remainder ) AS (
    SELECT NULL AS element, '1,2,3,4,5' AS remainder
        UNION ALL
    SELECT
        CASE
            WHEN INSTR( remainder, ',' )>0 THEN
                SUBSTR( remainder, 0, INSTR( remainder, ',' ) )
            ELSE
                remainder
        END AS element,
        CASE
            WHEN INSTR( remainder, ',' )>0 THEN
                SUBSTR( remainder, INSTR( remainder, ',' )+1 )
            ELSE
                NULL
        END AS remainder
    FROM list
    WHERE remainder IS NOT NULL
)
SELECT * FROM list;

（最初来自此博客post：https://blog.expensify.com/2015/09/25/the-simplest-sqlite-common-table-expression-tutorial）

它产生：

element | remainder
-------------------
NULL    | 1,2,3,4,5
1       | 2,3,4,5
2       | 3,4,5
3       | 4,5
4       | 5
5       | NULL

因此，问题是将其应用于 table 中的每一行。

Answer 1

是的，递归通用 table 表达式是解决方案：

with x(one, firstone, rest) as 
(select one, substr(many, 1, instr(many, ',')-1) as firstone, substr(many, instr(many, ',')+1) as rest from data where many like "%,%"
   UNION ALL
 select one, substr(rest, 1, instr(rest, ',')-1) as firstone, substr(rest, instr(rest, ',')+1) as rest from x    where rest like "%,%" LIMIT 200
)
select one, firstone from x UNION ALL select one, rest from x where rest not like "%,%" 
ORDER by one;

输出：

a|a1
a|a2
a|a3
b|b1
b|b3
c|c2
c|c1

Answer 2

检查我在 How to split comma-separated value in SQLite? 中的回答。这将在单个查询中为您提供转换，而不必应用于每一行。

-- using your data table assuming that b3 is suppose to be b2

WITH split(one, many, str) AS (
    SELECT one, '', many||',' FROM data
    UNION ALL SELECT one,
    substr(str, 0, instr(str, ',')),
    substr(str, instr(str, ',')+1)
    FROM split WHERE str !=''
) SELECT one, many FROM split WHERE many!='' ORDER BY one;

a|a1
a|a2
a|a3
b|b1
b|b2
c|c2
c|c1

使用 sqlite 将值拆分为多个部分

Split values in parts with sqlite

sqlite

recursive-query

common-table-expression