Related: Don't blindly use BIGINT for all numbers. And, if using utf8, that is 755 bytes for every row! (8.0 fixes this design flaw?) In this case, VARCHAR(255) becomes CHAR(255) for the temp table. Complex SELECTs may need a temp table, and may use MEMORY for it.You could overflow a limit on index size.If you have a lot of columns, you could hit a max row size limit and CREATE TABLE will fail.Potential negative impacts of blindly using '255': It can require less storage space than fixed-length types, because it uses only as much space as it needs (i.e., less space is used to store shorter values). (MD5 and UUID should be taken a step further, but that is another rant.) In MySQL, you can store UUID values in a compact format ( BINARY ) and display them in human-readable format ( VARCHAR ) with help of the following functions. according to High Performance MySQL book: VARCHAR stores variable-length character strings and is the most common string data type. Now, we create our domain class using Hibernate annotations to map it to our existing MySQL table. The rest of the table structure can be similar to the image. And almost always it should be CHARACTER SET ascii - country_code, postal_code, Y/N, M/F, MD5, UUID, base64, etc. Since we know the format of the UUID when represented as a String, we know that it has a length of 36 characters, so we can define the column as VARCHAR (36). Big enough to conservatively never be exceeded, yet.That is, this is not a valid excuse for using 255. See the MySQL page on CHAR and VARCHAR Types for a detailed explanation (be sure to also read the comments). If your content is a fixed size, you'll get better performance with CHAR. However, the choice of 1 or 2 is not driven only by the individual column it is driven by the total row size. 17 Answers Sorted by: 430 VARCHAR is variable-length.
#MYSQL UUID CHAR OR VARCHAR PLUS#
Some depend on Engine, some on CHARACTER SET, etc.Ī VARCHAR is stored as a 1- or 2-byte length plus enough bytes for the current text in whatever charset you have specified. In MySQL, there are reasons to stop at 191, 255, 767, 3071, 64K, and probably other values. you really need them because of generating unique ids from different places (and have not figured out another way to do it). Sure, there used to be some reasons for '255', but many are no longer valid, and even counter-productive. 1 2 yveslaptop: uuidgen 83fda883-86d9-4913-9729-91f20973fa52 There are officially 5 types of UUID values, version 1 to 5, but the most common are: time-based (version 1 or version 2) and purely random (version 3). We usually see people store UUID in char(36) or varchar(255), which waste the storage, and more importantly, slowing the performance. Generalization: The inefficiency applies to any 'random' access - UUID / MD5 / RAND () / etc.
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