MySQL中的字符串分割函数及基本用法详解

SUBSTRING_INDEX(str, delim, count)

-- 获取第一个逗号前的内容
SELECT SUBSTRING_INDEX('apple,banana,orange', ',', 1); 
-- 结果: 'apple'
-- 获取最后一个逗号后的内容
SELECT SUBSTRING_INDEX('apple,banana,orange', ',', -1); 
-- 结果: 'orange'
-- 获取前两个元素
SELECT 
  SUBSTRING_INDEX('apple,banana,orange', ',', 1) AS item1,
  SUBSTRING_INDEX(SUBSTRING_INDEX('apple,banana,orange', ',', 2), ',', -1) AS item2;
-- 结果: item1='apple', item2='banana'

-- 使用多字符作为分隔符
SELECT SUBSTRING_INDEX('apple||banana||orange', '||', 2);
-- 结果: 'apple||banana'
SELECT SUBSTRING_INDEX('apple||banana||orange', '||', -1);
-- 结果: 'orange'

-- 分隔符不存在时返回原字符串
SELECT SUBSTRING_INDEX('apple_banana_orange', ',', 1);
-- 结果: 'apple_banana_orange'
-- count超过实际分隔数时返回整个字符串
SELECT SUBSTRING_INDEX('apple,banana', ',', 5);
-- 结果: 'apple,banana'
-- 空字符串处理
SELECT SUBSTRING_INDEX('', ',', 1);
-- 结果: ''

-- 使用REGEXP_SUBSTR提取匹配的子串
SELECT REGEXP_SUBSTR('apple,banana,orange', '[^,]+', 1, 1) AS item1,
       REGEXP_SUBSTR('apple,banana,orange', '[^,]+', 1, 2) AS item2;
-- 结果: item1='apple', item2='banana'

DELIMITER //
CREATE PROCEDURE split_string(IN input_string VARCHAR(1000), IN delimiter_char VARCHAR(1))
BEGIN
    DECLARE temp_string VARCHAR(1000);
    DECLARE i INT DEFAULT 1;
    DECLARE item VARCHAR(1000);
    SET temp_string = input_string;
    WHILE LENGTH(temp_string) > 0 DO
        SET item = SUBSTRING_INDEX(temp_string, delimiter_char, 1);
        SELECT item AS split_result;
        SET temp_string = SUBSTRING(temp_string, LENGTH(item) + 2);
        IF LENGTH(temp_string) = 0 THEN
            LEAVE;
        END IF;
        SET i = i + 1;
    END WHILE;
END //
DELIMITER ;
-- 调用存储过程
CALL split_string('apple,banana,orange', ',');

-- 将逗号分隔的字符串转为JSON数组
SELECT 
  JSON_UNQUOTE(JSON_EXTRACT(CONCAT('["', REPLACE('apple,banana,orange', ',', '","'), '"]'), '$[0]')) AS item1,
  JSON_UNQUOTE(JSON_EXTRACT(CONCAT('["', REPLACE('apple,banana,orange', ',', '","'), '"]'), '$[1]')) AS item2;
-- 结果: item1='apple', item2='banana'

CREATE TABLE products (
    id INT,
    name VARCHAR(100),
    tags VARCHAR(255)
);
INSERT INTO products VALUES 
(1, 'Laptop', 'electronics,computer,premium'),
(2, 'Phone', 'electronics,mobile'),
(3, 'Desk', 'furniture,office');
-- 查询所有电子类产品
SELECT * FROM products 
WHERE FIND_IN_SET('electronics', tags) > 0;

select
    SUBSTRING_INDEX (profile, ',', -1) as gender,
    count(*) as number
from
    user_submit 
group by
    gender

select
    device_id,
    substring_index (blog_url, "/", -1) as user_name
from
    user_submit

select
    substring_index (substring_index (profile, ",", 3), ",", -1) as age,
    count(*) as number
from
    user_submit
group by
    age

select
    # SUBSTRING_INDEX (order_id, '_', -1) as product_id,
    regexp_substr(order_id,'p[0-9]+$') as product_id,
    count(*) as cnt
from order_log
group by product_id
order by cnt desc,product_id asc;