Changing Data and Structure - Mastering phpMyAdmin 3.4 for Effective MySQL Management - page 104

Although MEDIUMTEXT , TEXT , and LONGTEXT column types can
accommodate more than 32 KiB of data, some browsers cannot always
edit them with the text area—the mechanism offered by HTML. In
fact, experimentation has convinced the phpMyAdmin development
team to have the product display a warning message if the contents
are larger than 32 KiB. The message warns users that the contents may
not be editable.
The last configuration directive, $cfg['LongtextDoubleTextarea'] , has an impact
for LONGTEXT column types only. The default value of TRUE doubles the available
editing space.
BLOB (Binary Large Object) column type
BLOB column types are generally used to hold binary data (such as images and
sounds), even though the MySQL documentation implies that TEXT column
types could be used for this purpose. The MySQL 5.1 manual says: "In some cases,
it may be desirable to store binary data such as media files in BLOB or TEXT
columns". However, another phrase: "BLOB columns are treated as binary strings
(byte strings)", seems to indicate that binary data should really be stored in BLOB
columns. Thus, phpMyAdmin's intention is to work with the BLOB column type to
hold all binary data.
We will see in Chapter 16 that there are special mechanisms available to go further
with BLOB column type, including being able to view some images directly from
within phpMyAdmin.
First, we add a BLOB column type named cover_photo to our topic table. If we now
browse the table, we can see the length information, [BLOB - 0B] , for each BLOB
column type.
This is because the Show BLOB display option (do you remember the Options
slider?) has no check mark by default. So, it blocks the display of BLOB contents in
Browse mode. This behavior is intentional. Usually, we cannot do anything with
binary data represented in plain text.