Split delimited string value into rows

问题

Some external data vendor wants to give me a data field - pipe delimited string value, which I find quite difficult to deal with.

Without help from an application programming language, is there a way to transform the string value into rows?

There is a difficulty however, the field has unknown number of delimited elements.

DB engine in question is MySQL.

For example:

Input: Tuple(1, "a|b|c")

Output:

Tuple(1, "a")
Tuple(1, "b")
Tuple(1, "c")

回答1:

It may not be as difficult as I initially thought.

This is a general approach:

Count number of occurrences of the delimiter length(val) - length(replace(val, '|', ''))
Loop a number of times, each time grab a new delimited value and insert the value to a second table.

回答2:

Use this function by Federico Cargnelutti:

 CREATE FUNCTION SPLIT_STR(
 x VARCHAR(255),
 delim VARCHAR(12),
 pos INT
 )
   RETURNS VARCHAR(255)
   RETURN REPLACE(SUBSTRING(SUBSTRING_INDEX(x, delim, pos),LENGTH(SUBSTRING_INDEX(x, delim, pos -1)) + 1),
delim, '');

Usage

 SELECT SPLIT_STR(string, delimiter, position)

you will need a loop to solve your problem.

回答3:

Although your issue is probably long time resolved, I was looking for a solution to the very same problem you had. I solved it with the help of a procedure referenced here with slight adaptions to serve multi-byte characters (such as the German Umlauts) in the string by using CHAR_LENGTH() instead of LENGTH().

DELIMITER $$
    CREATE FUNCTION SPLIT_STRING(val TEXT, delim VARCHAR(12), pos INT) RETURNS TEXT
    BEGIN
        DECLARE output TEXT;
        SET output = REPLACE(SUBSTRING(SUBSTRING_INDEX(val, delim, pos), CHAR_LENGTH(SUBSTRING_INDEX(val, delim, pos - 1)) + 1), delim, '');
        IF output = '' THEN
            SET output = null;
        END IF;
        RETURN output;
    END $$

    CREATE PROCEDURE TRANSFER_CELL()
    BEGIN
        DECLARE i INTEGER;
        SET i = 1;
        REPEAT
            INSERT INTO NewTuple (id, value)
            SELECT id, SPLIT_STRING(value, '|', i)
            FROM Tuple
            WHERE SPLIT_STRING(value, '|', i) IS NOT NULL;
            SET i = i + 1;
        UNTIL ROW_COUNT() = 0
        END REPEAT;
    END $$
DELIMITER ;

CALL TRANSFER_CELL() ;

DROP FUNCTION SPLIT_STRING ;
DROP PROCEDURE TRANSFER_CELL ;

来源：https://stackoverflow.com/questions/18304857/split-delimited-string-value-into-rows

标签

mysql

sql

database

delimiter