{"version":"https://jsonfeed.org/version/1.1","title":"Vic Demuzere - SQLite","home_page_url":"https://vic.demuzere.be/articles/tags/sqlite/","feed_url":"https://vic.demuzere.be/articles/tags/sqlite/feed.json","description":"Blog posts tagged SQLite by Vic Demuzere","language":"en","items":[{"id":"https://vic.demuzere.be/articles/generating-uuids-in-sqlite/","content_html":"

SQLite does not have built-in UUID functions, but by getting creative with the randomblob(N) function we can generate version 4 (random) UUIDs.

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Before we continue, it's important to note that you should verify whether SQLite's random functions are adequate for your usecase.\nThey may not return truly random data.\nHowever, as the RFC notes, "they (UUIDs) MUST NOT be used as security capabilities".\nAnd since we all follow that to the letter, it doesn't really matter.. right?

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The excellent SQLite manual gives us a starting point:

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Hint: applications can generate globally unique identifiers using this function together with hex() and/or lower().

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Combining the randomblob(N) function with hex(N) does indeed create something that vaguely resembles a UUID.\nFor some purposes this may suffice, but the result isn't actually a valid UUID1:\nvalid UUIDs must have specific bits set to indicate their version and variant.

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We can do better!

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As binary blob

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The binary representation of a version 4 UUID consists of:

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As far as I know, we can't modify individual bytes in a blob using the available functions in SQLite.\nHowever, we do have access to a lot of string functions.\nTaking a detour using HEX encoding provides a solution.\nWe'll first concatenate a HEX string containing the data we want, then convert it back to a binary blob.\nNote that each byte is represented by two hexadecimal characters.

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The first 48 random bits are easy:

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sqlite> select HEX(RANDOMBLOB(6));\r\n4004714237AF\r\n
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The first 4 bits of the next byte need to be set to 0100 (or 4 in hex).\nAs every byte is represented by two characters in hexadecimal, we can just use a literal 4 for the next character.

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sqlite> select '4';\r\n4\r\n
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Next, we need 6 bits of random data.\nWe can only generate random bytes using RANDOMBLOB(N), but we need 1.5 bytes.\nLuckily, because we are working with a hexadecimal string, we can generate 2 bytes (4 hex characters) and take the first three characters.

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sqlite> select HEX(RANDOMBLOB(2));\r\n7B4A\r\n\r\nsqlite> select SUBSTR(HEX(RANDOMBLOB(2)),0,4);\r\n5BD\r\n
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The next one is a little more complex.\nThe variant field consists of a variable number of bits.\nFor our version 4 UUID, we need to set the first two bits to 10, the others can be random.\nThat gives us a possible range between 1000 and 1011, or a hexadecimal character between 8 and B inclusive.

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select FORMAT('%X', 8 + ABS(RANDOM() % 4));\r\nA\r\n
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After this, we need 60 more random bits.\nSince this again includes a half byte again (7.5 bytes), we're doing the same SUBSTR trick as before:

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sqlite> select SUBSTR(HEX(RANDOMBLOB(8)),0,16);\r\nE83EF2136842130\r\n
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Stitching it together

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Using CONCAT(X, ...) we create a single string:

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sqlite> select CONCAT(\r\n(x1...>   HEX(RANDOMBLOB(6)),\r\n(x1...>   '4',\r\n(x1...>   SUBSTR(HEX(RANDOMBLOB(2)),0,4),\r\n(x1...>   FORMAT('%X', 8 + ABS(RANDOM() % 4)),\r\n(x1...>   SUBSTR(HEX(RANDOMBLOB(8)),0,16)\r\n(x1...> );\r\n\r\n64DF281823BE47249BB2CA8D6450066B\r\n
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Then use UNHEX(X) to convert it back into a binary blob:

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select UNHEX(CONCAT(\r\n  HEX(RANDOMBLOB(6)),\r\n  '4',\r\n  SUBSTR(HEX(RANDOMBLOB(2)),0,4),\r\n  FORMAT('%X', 8 + ABS(RANDOM() % 4)),\r\n  SUBSTR(HEX(RANDOMBLOB(8)),0,16)\r\n));\r\n
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Generating UUIDs automatically

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The SQL above can be used as the default value for a blob column:

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CREATE TABLE "animals" (\r\n  "id" INTEGER PRIMARY KEY NOT NULL,\r\n  "uuid" BLOB UNIQUE NOT NULL\r\n    DEFAULT (UNHEX(CONCAT(\r\n      HEX(RANDOMBLOB(6)), '4',\r\n      SUBSTR(HEX(RANDOMBLOB(2)),0,4),\r\n      FORMAT('%X', 8 + ABS(RANDOM() % 4)),\r\n      SUBSTR(HEX(RANDOMBLOB(8)),0,16))))\r\n    UNIQUE CHECK(LENGTH("uuid") = 16),\r\n   "name" TEXT NOT NULL\r\n) STRICT;\r\n
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This will generate a UUID if we don't specify one on insert:

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sqlite> INSERT INTO "animals" ("name") VALUES ('Fluffy');\r\n\r\nsqlite> SELECT * FROM "animals";\r\n1|[blob]|Fluffy\r\n\r\nsqlite> SELECT "id", HEX("uuid"), "name" FROM "animals";\r\n1|85671F7120F14AA6802B8B4E9213B8BE|Fluffy\r\n
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In human readable (hexadecimal) form

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Depending on your use case, you may want to store UUIDs in a TEXT column.

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We were close to a "hex-and-dash" string format with the SQL above, until we call the UNHEX(X) function.\nRFC 9562 specifies that dashes are required, so we'll add them in the right places.

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sqlite> select CONCAT(\r\n  HEX(RANDOMBLOB(4)),\r\n  '-',\r\n  HEX(RANDOMBLOB(2)),\r\n  '-',\r\n  '4',\r\n  SUBSTR(HEX(RANDOMBLOB(2)),0,4),\r\n  '-',\r\n  FORMAT('%X', 8 + ABS(RANDOM() % 4)),\r\n  SUBSTR(HEX(RANDOMBLOB(2)),0,4),\r\n  '-',\r\n  SUBSTR(HEX(RANDOMBLOB(8)),0,13)\r\n);\r\n\r\n199ED82A-3102-42DB-B59B-8C356B6F3FF7\r\n
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Voila!

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    As technically correct is the best kind of correct: if you get really lucky with the generated random data, they might actually be valid. ↩

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Feel free to e-mail comments or corrections to vic@demuzere.be.

","url":"https://vic.demuzere.be/articles/generating-uuids-in-sqlite/","date_published":"2025-12-24T15:28:41Z","date_modified":"2026-01-04T17:26:44Z","language":"en"}]}