Unique random string generator, MySQL

Language: Layout:

DROP TABLE IF EXISTS submissions;
CREATE TABLE submissions(
  submissionId INT NOT NULL AUTO_INCREMENT,
  stringId VARCHAR(5),
  PRIMARY KEY (submissionId));

DROP FUNCTION IF EXISTS uniqueId;
CREATE FUNCTION uniqueId() RETURNS VARCHAR(5)
  DETERMINISTIC
BEGIN
  DECLARE uniqueID VARCHAR(5);
  DECLARE allChars VARCHAR(62);
  DECLARE seed INT;
  SET @seed = RAND() * 4294967295;
  SET @allChars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
  WHILE @uniqueId IS NULL OR EXISTS (SELECT stringId FROM submissions WHERE stringId = @uniqueId) DO
    SET @uniqueId = CONCAT(
                SUBSTRING(@allchars, RAND(@seed := ROUND(RAND(@seed) * 4294967295)) * 62 + 1, 1),
                SUBSTRING(@allchars, RAND(@seed := ROUND(RAND(@seed) * 4294967295)) * 62 + 1, 1),
                SUBSTRING(@allchars, RAND(@seed := ROUND(RAND(@seed) * 4294967295)) * 62 + 1, 1),
                SUBSTRING(@allchars, RAND(@seed := ROUND(RAND(@seed) * 4294967295)) * 62 + 1, 1),
                SUBSTRING(@allchars, RAND(@seed := ROUND(RAND(@seed) * 4294967295)) * 62 + 1, 1));
  END WHILE;
              
  RETURN @uniqueId;
END;

INSERT INTO submissions (stringId) SELECT uniqueId();
INSERT INTO submissions (stringId) SELECT uniqueId();
INSERT INTO submissions (stringId) SELECT uniqueId();
INSERT INTO submissions (stringId) SELECT uniqueId();
INSERT INTO submissions (stringId) SELECT uniqueId();

SELECT * FROM submissions;


absolute service time: 0,37 sec