MySQL 8.0

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select version();

version()

8.0.23

SELECT SUBSTRING("SQL Tutorial", 5, 3) AS ExtractString;

ExtractString

Tut

CREATE TABLE test
(
  ip_v6 VARCHAR (39) NOT NULL PRIMARY KEY,
  host VARCHAR (100) NOT NULL,
  ip_v6_token_1 VARCHAR (4) GENERATED ALWAYS AS (SUBSTRING (ip_v6, 1, 4)) STORED
);
Expression of generated column 'ip_v6_token_1' contains a disallowed function: `SUBSTRING`.