mysql - 拆分字符串并循环遍历 MySQL 存储过程中的值

Question

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

例如，如果我将“jhon,swetha,sitha”字符串传递给 MySQL 存储过程，那么它必须用逗号分隔该字符串，并将这些值作为 3 条记录插入表中。

  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

但这不起作用。请问有什么解决办法吗？

Answer 1

您需要更加小心地处理字符串操作。您不能为此使用 REPLACE() ，因为这会替换多次出现的情况，如果逗号分隔列表中的一个元素是另一元素的子字符串，则会损坏您的数据。 INSERT() string function这样做更好，不要与用于插入表的 INSERT 语句混淆。

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)

调用该过程。

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

请注意，“1 行受影响”并不意味着您所期望的。它指的是我们最后一次插入的内容。由于我们一次插入一行，因此如果该过程插入至少一行，则行数始终为 1；如果该过程不插入任何内容，则 0 行将受到影响。

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)