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I've got a messages table in MySQL which records messages between users. Apart from the typical ids and message types (all integer types) I need to save the actual message text as either VARCHAR or TEXT. I'm setting a front-end limit of 3000 characters which means the messages would never be inserted into the db as longer than this.
Is there a rationale for going with either VARCHAR(3000) or TEXT? There's something about just writing VARCHAR(3000) that feels somewhat counter-intuitive. I've been through other similar posts on Stack Overflow but would be good to get views specific to this type of common message storing.
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In most circumstances, VARCHAR provides better performance, it's more flexible, and can be fully indexed. If you need to store longer strings, use MEDIUMTEXT or LONGTEXT, but be aware that very large amounts of data can be stored in columns of these types.
Yes, is matter when you indexing multiple columns.
Use varchar if you want to have a length constraint. Use string if you don't want to restrict the length of the text.
LONGTEXT can store the maximum characters among all four, up to 4,294,967,295 characters i,e 4,294,967,295 bytes or 4GB. This is more than enough storage for any long-form text strings. For example, a book that MEDIUMTEXT can't hold can be stored using LONGTEXT. LONGTEXT takes 4-Bytes overhead.
TEXT and BLOB may by stored off the table with the table just having a pointer to the location of the actual storage. Where it is stored depends on lots of things like data size, columns size, row_format, and MySQL version.
VARCHAR is stored inline with the table. VARCHAR is faster when the size is reasonable, the tradeoff of which would be faster depends upon your data and your hardware, you'd want to benchmark a real-world scenario with your data.
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Can you predict how long the user input would be?
VARCHAR(X)
Max Length: variable, up to 65,535 bytes (64KB)
Case: user name, email, country, subject, password
TEXT
Max Length: 65,535 bytes (64KB)
Case: messages, emails, comments, formatted text, html, code, images, links
MEDIUMTEXT
Max Length: 16,777,215 bytes (16MB)
Case: large json bodies, short to medium length books, csv strings
LONGTEXT
Max Length: 4,294,967,29 bytes (4GB)
Case: textbooks, programs, years of logs files, harry potter and the goblet of fire, scientific research logging
There's more information on this question.
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