sql – How do I convert from BLOB to TEXT in MySQL?

The Question :

225 people think this question is useful

I have a whole lot of records where text has been stored in a blob in MySQL. For ease of handling I’d like to change the format in the database to TEXT… Any ideas how easily to make the change so as not to interrupt the data – I guess it will need to be encoded properly?

The Question Comments :

The Answer 1

278 people think this answer is useful

That’s unnecessary. Just use SELECT CONVERT(column USING utf8) FROM….. instead of just SELECT column FROM

The Answer 2

130 people think this answer is useful

Here’s an example of a person who wants to convert a blob to char(1000) with UTF-8 encoding:

CAST(a.ar_options AS CHAR(10000) CHARACTER SET utf8)

This is his answer. There is probably much more you can read about CAST right here. I hope it helps some.

The Answer 3

16 people think this answer is useful

I have had the same problem, and here is my solution:

  1. create new columns of type text in the table for each blob column
  2. convert all the blobs to text and save them in the new columns
  3. remove the blob columns
  4. rename the new columns to the names of the removed ones
ALTER TABLE mytable
ADD COLUMN field1_new TEXT NOT NULL,
ADD COLUMN field2_new TEXT NOT NULL;

update mytable set
field1_new = CONVERT(field1 USING utf8),
field2_new = CONVERT(field2 USING utf8);

alter table mytable
drop column field1,
drop column field2;

alter table mytable
change column field1_new field1 text,
change column field2_new field2 text;

The Answer 4

9 people think this answer is useful

You can do it very easily.

ALTER TABLE `table_name` CHANGE COLUMN `column_name` `column_name` LONGTEXT NULL DEFAULT NULL ;

The above query worked for me. I hope it helps you too.

The Answer 5

9 people think this answer is useful

If you are using MYSQL-WORKBENCH, then you can select blob column normally and right click on column and click open value in editor. refer screenshot:

screenshot

The Answer 6

2 people think this answer is useful

Or you can use this function:

DELIMITER $$

CREATE FUNCTION BLOB2TXT (blobfield VARCHAR(255)) RETURNS longtext
DETERMINISTIC
NO SQL
BEGIN
       RETURN CAST(blobfield AS CHAR(10000) CHARACTER SET utf8);
END
$$


DELIMITER ;

The Answer 7

2 people think this answer is useful

None of these answers worked for me. When converting to UTF8, when the encoder encounters a set of bytes it can’t convert to UTF8 it will result in a ? substitution which results in data loss. You need to use UTF16:

SELECT
    blobfield,
    CONVERT(blobfield USING utf16),
    CONVERT(CONVERT(blobfield USING utf16), BINARY),
    CAST(blobfield  AS CHAR(10000) CHARACTER SET utf16),
    CAST(CAST(blobfield  AS CHAR(10000) CHARACTER SET utf16) AS BINARY)

You can inspect the binary values in MySQL Workbench. Right click on the field -> Open Value in Viewer-> Binary. When converted back to BINARY the binary values should be the same as the original.

Alternatively, you can just use base-64 which was made for this purpose:

SELECT
    blobfield,
    TO_BASE64(blobfield),
    FROM_BASE64(TO_BASE64(blobfield))

The Answer 8

2 people think this answer is useful

phpMyAdmin screenshot Using phpMyAdmin you can also set the options to show BLOB content and show complete text.

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