如何在表中将所有空字符串更改为NULL？

Question

我有一个约100列(90%可空)的遗留表.在这90个列中,我想删除所有空字符串并将它们设置为null.我知道我可以:

update table set column = NULL where column = '';
update table set column2 = NULL where column2 = '';

但这很乏味且容易出错.在整个桌子上必须有一种方法吗？

Answer 1

UPDATE
    TableName
SET
    column01 = CASE column01 WHEN '' THEN NULL ELSE column01 END,
    column02 = CASE column02 WHEN '' THEN NULL ELSE column02 END,
    column03 = CASE column03 WHEN '' THEN NULL ELSE column03 END,
    ...,
    column99 = CASE column99 WHEN '' THEN NULL ELSE column99 END

这仍然是手动完成的,但比你的痛苦略少,因为它不需要你为每一列发送查询.除非你想要编写脚本的麻烦,否则在做这样的事情时你将不得不忍受一定的痛苦.

编辑:添加了ENDs

Answer 2

一个可能的脚本:

for col in $(echo "select column_name from information_schema.columns
where table_name='$TABLE'"|mysql --skip-column-names $DB)
do
echo update $TABLE set $col = NULL where $col = \'\'\;
done|mysql $DB

Answer 3

对于新手,在看到上述答案后,您可能仍需要更多工作.输入数千行是不现实的.所以在这里我提供了一个完整的工作代码,以避免语法错误等.

DROP PROCEDURE IF EXISTS processallcolumns;

DELIMITER $$

CREATE PROCEDURE processallcolumns ()
BEGIN

  DECLARE i,num_rows INT ;
  DECLARE col_name char(250);

  DECLARE col_names CURSOR FOR
  SELECT column_name
  FROM INFORMATION_SCHEMA.COLUMNS
  WHERE table_name = 'PROCESSINGTABLE'
  ORDER BY ordinal_position;

  OPEN col_names ;
  select FOUND_ROWS() into num_rows;

  SET i = 1;
  the_loop: LOOP

     IF i > num_rows THEN
          CLOSE col_names;
          LEAVE the_loop;
      END IF;


      FETCH col_names 
      INTO col_name;     


      SET @command_text = CONCAT('UPDATE `PROCESSINGTABLE` SET ', col_name, '= IF(LENGTH(', col_name, ')=0, NULL,', col_name, ') WHERE 1 ;' ) ;

--      UPDATE `PROCESSINGTABLE` SET col_name=IF(LENGTH(col_name)=0,NULL,col_name) WHERE 1;
--      This won't work, because MySQL doesn't take varibles as column name.

      PREPARE stmt FROM @command_text ;
      EXECUTE stmt ;

      SET i = i + 1;  
  END LOOP the_loop ;



END$$
DELIMITER ;

call processallcolumns ();
DROP PROCEDURE processallcolumns;