MySQL中列值分割的几种方法

CREATE TABLE orders (
  id INT PRIMARY KEY,
  items VARCHAR(100)   -- 用逗号分隔的商品串
);

INSERT INTO orders VALUES
(1,'苹果,香蕉,橙子'),
(2,'芒果'),
(3,'桃子,葡萄'),
(4,'');

SELECT id,
       SUBSTRING_INDEX(items, ',', 1)                         AS item1,
       SUBSTRING_INDEX(SUBSTRING_INDEX(items, ',', 2), ',', -1) AS item2,
       SUBSTRING_INDEX(items, ',', -1)                        AS item_last
FROM orders;

WITH RECURSIVE nums(n) AS (
  SELECT 1 UNION ALL SELECT n+1 FROM nums WHERE n<20
)
SELECT o.id, o.items,
       TRIM(SUBSTRING_INDEX(SUBSTRING_INDEX(o.items, ',', n), ',', -1)) AS item
FROM orders o
JOIN nums
  ON n <= 1 + LENGTH(o.items) - LENGTH(REPLACE(o.items, ',', ''));

SELECT o.id, t.item
FROM orders o,
JSON_TABLE(
  CONCAT('["', REPLACE(items, ',', '","'), '"]'),  -- 变成 ["苹果","香蕉","橙子"]
  "$[*]" COLUMNS(item VARCHAR(20) PATH "$")
) AS t;

SELECT id,
       REGEXP_SUBSTR(items, '[^,]+', 1, 1) AS item1,
       REGEXP_SUBSTR(items, '[^,]+', 1, 2) AS item2,
       REGEXP_SUBSTR(items, '[^,]+', 1, 3) AS item3
FROM orders;