contador campos em branco/null, MySQL

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DROP TABLE IF EXISTS tabela, tabela_colunas, tabela_contador;
DROP PROCEDURE IF EXISTS CamposEmBraco;

CREATE TABLE tabela (
  id int,
  endereco varchar(100),
  telefone varchar(15),
  etc varchar(255));

INSERT INTO tabela (id, endereco, telefone, etc) VALUES
(1, 'rua 1', '123', 'etc'),
(2, 'rua 2', '', NULL),
(3, 'rua 3', NULL, 'cte');

create table tabela_colunas (id int, coluna varchar(100));

SET @row_number := 0;
INSERT INTO tabela_colunas (id, coluna)
SELECT (@row_number:=@row_number + 1) AS id, column_name as coluna FROM information_schema.columns
WHERE table_name = 'tabela';

CREATE TABLE tabela_contador (
  id_na_tabela int(10),
  total int(1));

CREATE PROCEDURE CamposEmBraco()
BEGIN
    SET @id_tabela:=1, @total:=(SELECT COUNT(*) FROM tabela_colunas);
    
    insert into tabela_contador (id_na_tabela, total)
    select id, 0 as total from tabela;

WHILE @id_tabela <= @total DO
    
        set @sql := concat('update tabela_contador tc join tabela t on tc.id_na_tabela = t.id set tc.total = tc.total + 1 where ', (select coluna from tabela_colunas where id = @id_tabela), ' is null or ', (select coluna from tabela_colunas where id = @id_tabela), ' = \'\'');

PREPARE myquery FROM @sql;
        EXECUTE myquery;

SET @id_tabela = @id_tabela + 1;    
    END WHILE;
    
    select * from tabela_contador;
END;

call CamposEmBraco();


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