How do I convert from BLOB to TEXT in MySQL?

问题

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?

回答1:

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

回答2:

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.

回答3:

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

create new columns of type text in the table for each blob column
convert all the blobs to text and save them in the new columns
remove the blob columns
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;

回答4:

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.

回答5:

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:

回答6:

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 ;

回答7:

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))

来源：https://stackoverflow.com/questions/948174/how-do-i-convert-from-blob-to-text-in-mysql

标签

sql

mysql

blobs