sequenceをマルチゾーンとして配備するid

-- sequence 
DROP TABLE IF EXISTS sequence;
--  sequence ，  seq     ，   ：0(default) 9223372036854775807（0 2^63–1）。
CREATE TABLE sequence (
name            VARCHAR(50) NOT NULL,      --   
current_value   BIGINT NOT NULL DEFAULT 0, --    
increment       INT NOT NULL DEFAULT 1,    --   
PRIMARY KEY (name)  --      seq   
) ENGINE=InnoDB;

-- DELIMITER         ，                    
DELIMITER /
DROP FUNCTION IF EXISTS currval /
CREATE FUNCTION currval(seq_name VARCHAR(50))
RETURNS BIGINT
BEGIN
    DECLARE value BIGINT;
    SELECT current_value INTO value
    FROM sequence
    WHERE upper(name) = upper(seq_name); --       .
    RETURN value;
END;
/
DELIMITER ;

DELIMITER /
DROP FUNCTION IF EXISTS nextval /
CREATE FUNCTION nextval (seq_name VARCHAR(50))
RETURNS BIGINT
BEGIN
    DECLARE value BIGINT;
    UPDATE sequence
    SET current_value = current_value + increment
    WHERE upper(name) = upper(seq_name);
    RETURN currval(seq_name);
END;
/
DELIMITER ;