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Mysql uuid char or varchar7/14/2023 ![]() ![]() uuid CHAR(36) CHARACTER SET ascii In contrast to CHAR, VARCHAR values are stored as a 1-byte or 2-byte length prefix plus data. If I’m wrong about what I took away from reading today, please let me know in the comments. If you always have a UUID for each row, you could store it as CHAR(36) and save 1 byte per row over VARCHAR(36). Storing UUIDs in a non-character column could make sense, but since UUID() returns characters anyway, it’s going against the grain.Ĭonclusion: Use the CHAR(36) type in MySQL. As you can find there can be mapped to diferent types (binary or char/varchar).The varchar columns in the table are of variable length string that can hold either numeric or character or both. 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). But here comes the problem, using it as PRIMARY KEY causes the problems described below. varchar takes extra memory to store a prefix, which I presume to describe the length which char would not need Varchar in MySQL is a data type used for storing text whose length can have a maximum of 65535 characters. Many people store UUID as char (36) and use as row identity value (PRIMARY KEY) because it is unique across every table, every database and every server and allow easy merging of records from different databases.I answered, after trying it, UPDATE table SET uuidcol UUID () It worked for me, but about half (it seems) people report that it doesn't work, saying the ID is identical on all rows. See the MySQL page on CHAR and VARCHAR Types for a detailed explanation (be sure to also read the comments). As you can see, a UUID is a sequence of 32 digits of hexadecimal digits represented in groups separated by hyphens. 2 4 years ago, I answered a question on SO, 'how to set an UUID for each row in bulk'. If your content is a fixed size, you'll get better performance with CHAR. It’s more likely to make a difference if the column is indexed ( source) 17 Answers Sorted by: 430 VARCHAR is variable-length.( This post claimed a 20% speed improvement by switching to ROW_FORMAT=fixed, which seems related but maybe not the same.) The number of variable-width columns in a row can make a significant difference in performance.Also, PostgreSQL has a native UUID type, so it’s kind of a wash. While doing this, I discovered that about half our UUIDs are v1, and the other half are v4. I was recently asked to add a column to this table of VARCHAR(32) that stores the non-dashed UUID hex. They are stored in the standard VARBINARY(16). PostgeSQL stores char and varchar columns the same way, so any performance boost in MySQL wouldn’t be reflected in PostgreSQL ( source) I have a MySQL InnoDB table with tens of millions of rows. Both MySQL and PostgeSQL support the same syntax for declaring char columns.It does seem like it could make an improvement, but not enough to be worth the effort in our case. I spent some time today evaluating whether switching columns that store UUIDs from varchar(255) to char(36) (or binary, etc) would result in any noticeable performance improvement in MySQL. ![]()
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