拆分字符串并循环遍历 MySql 过程中的值

2021-11-20 00:00:00 sql mysql stored-procedures

我遇到了一种情况，我必须将逗号分隔的字符串传递给 MySQL 过程并拆分该字符串并将这些值作为行插入到表中.

I got a situation where I have to pass a comma separated string to MySQL procedure and split that string and insert those values as rows in to a table.

如下图

例如，如果我将 'jhon,swetha,sitha' 字符串传递给 mysql 程序，那么它必须用逗号分割该字符串并将这些值作为 3 条记录插入到表中.

For example if I passed 'jhon,swetha,sitha' string to mysql procedure then it have to split that string by comma and insert those values as 3 records into a table.

  CREATE PROCEDURE new_routine (IN str varchar(30))   
   BEGIN
       DECLARE tmp varchar(10);
       DECLARE inc INT DEFAULT 0; 
       WHILE INSTR(str, ',') DO
         SET tmp = SUBSTRING(SUBSTRING_INDEX(str,',',inc),LENGTH(SUBSTRING_INDEX(str,',',inc-1))+1),',','');
         SET str = REPLACE(str, tmp, '');
         //insert tmp into a table.
       END WHILE;
    END

但这并没有解决任何问题.

But this does not worked any solution please.

推荐答案

您需要更加小心地处理字符串.您不能为此使用 REPLACE()，因为这将替换多次出现，如果逗号分隔列表中的一个元素是另一个元素的子字符串，则会损坏您的数据.INSERT() 字符串function 对此更好，不要与用于插入表的 INSERT 语句混淆.

You'll need to be a little more careful with your string manipulation. You can't use REPLACE() for this, because that will replace multiple occurrences, corrupting your data if one element in the comma-separated list is a substring of another element. The INSERT() string function is better for this, not to be confused with the INSERT statement used for inserting into a table.

DELIMITER $$

DROP PROCEDURE IF EXISTS `insert_csv` $$
CREATE PROCEDURE `insert_csv`(_list MEDIUMTEXT)
BEGIN

DECLARE _next TEXT DEFAULT NULL;
DECLARE _nextlen INT DEFAULT NULL;
DECLARE _value TEXT DEFAULT NULL;

iterator:
LOOP
  -- exit the loop if the list seems empty or was null;
  -- this extra caution is necessary to avoid an endless loop in the proc.
  IF CHAR_LENGTH(TRIM(_list)) = 0 OR _list IS NULL THEN
    LEAVE iterator;
  END IF;
 
  -- capture the next value from the list
  SET _next = SUBSTRING_INDEX(_list,',',1);

  -- save the length of the captured value; we will need to remove this
  -- many characters + 1 from the beginning of the string 
  -- before the next iteration
  SET _nextlen = CHAR_LENGTH(_next);

  -- trim the value of leading and trailing spaces, in case of sloppy CSV strings
  SET _value = TRIM(_next);

  -- insert the extracted value into the target table
  INSERT INTO t1 (c1) VALUES (_value);

  -- rewrite the original string using the `INSERT()` string function,
  -- args are original string, start position, how many characters to remove, 
  -- and what to "insert" in their place (in this case, we "insert"
  -- an empty string, which removes _nextlen + 1 characters)
  SET _list = INSERT(_list,1,_nextlen + 1,'');
END LOOP;

END $$

DELIMITER ;

接下来是一个测试表:

CREATE TABLE `t1` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `c1` varchar(64) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

新表是空的.

mysql> SELECT * FROM t1;
Empty set (0.00 sec)

调用程序.

mysql> CALL insert_csv('foo,bar,buzz,fizz');
Query OK, 1 row affected (0.00 sec)

注意1 行受影响"并不意味着您的期望.它指的是我们所做的最后一次插入.由于我们一次插入一行，如果该过程插入至少一行，则行数总是为 1；如果过程没有插入任何内容，您将得到 0 行影响.

Note the "1 row affected" does not mean what you would expect. It refers to the last insert we did. Since we insert one row at a time, if the procedure inserts at least one row, you'll always get a row count of 1; if the procedure inserts nothing, you'll get 0 rows affected.

成功了吗?

mysql> SELECT * FROM t1;
+----+------+
| id | c1   |
+----+------+
|  1 | foo  |
|  2 | bar  |
|  3 | buzz |
|  4 | fizz |
+----+------+
4 rows in set (0.00 sec)

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