MySQL 8.0

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CREATE TABLE t (
  a VARCHAR(10)
      CHARACTER SET latin1
      COLLATE latin1_german1_ci
    NOT NULL
    DEFAULT 'abc'
);
SELECT
  table_name, column_name, column_default, is_nullable,
  character_maximum_length, character_set_name, collation_name
FROM 
    information_schema.columns
WHERE 
    TABLE_NAME = 't';


TABLE_NAME
COLUMN_NAME
COLUMN_DEFAULT
IS_NULLABLE
CHARACTER_MAXIMUM_LENGTH
CHARACTER_SET_NAME
COLLATION_NAME


t
a
616263
NO
10
latin1
latin1_german1_ci


-- let's "merely" extend the column's max len
ALTER TABLE t MODIFY a VARCHAR(20); 

Records: 0  Duplicates: 0  Warnings: 0


-- observe we lost the NOT NULL constraint, default value, charset, etc.
SELECT
  table_name, column_name, column_default, is_nullable,
  character_maximum_length, character_set_name, collation_name
FROM 
    information_schema.columns
WHERE 
    TABLE_NAME = 't';


TABLE_NAME
COLUMN_NAME
COLUMN_DEFAULT
IS_NULLABLE
CHARACTER_MAXIMUM_LENGTH
CHARACTER_SET_NAME
COLLATION_NAME


t
a
null
YES
20
utf8mb4
utf8mb4_0900_ai_ci