Changing column collation and character set in mysql database / schema

In the examples below, change: 

• <yourDB> to your actual database name
• <charset> to either utf8 or utf8mb4
• <collation> to either utf8_bin or utf8mb4_bin

To create the ALTER SQLs, run the below SQL and use the ALTER SQLs in the resultset to update the collation for varchar columns:

SELECT CONCAT('ALTER TABLE `', table_name, '` MODIFY `', column_name, '` ', DATA_TYPE, '(', CHARACTER_MAXIMUM_LENGTH, ') CHARACTER SET <charset> COLLATE <collation>', (CASE WHEN IS_NULLABLE = 'NO' THEN ' NOT NULL' ELSE '' END), ';')
FROM information_schema.COLUMNS 
WHERE TABLE_SCHEMA = '<yourDB>'
AND DATA_TYPE = 'varchar'
AND
(
    CHARACTER_SET_NAME != '<charset>'
    OR
    COLLATION_NAME != '<collation>'
);

To create the ALTER SQLs, run the below SQL and use the ALTER SQLs in the resultset to update the collation for non-varchar columns:

SELECT CONCAT('ALTER TABLE `', table_name, '` MODIFY `', column_name, '` ', DATA_TYPE, ' CHARACTER SET <charset> COLLATE <collation>', (CASE WHEN IS_NULLABLE = 'NO' THEN ' NOT NULL' ELSE '' END), ';')
FROM information_schema.COLUMNS 
WHERE TABLE_SCHEMA = '<yourDB>'
AND DATA_TYPE != 'varchar'
AND
(
    CHARACTER_SET_NAME != '<charset>'
    OR
    COLLATION_NAME != '<collation>'
);

You might also need to make sure that your collation and character set are properly defined at your my.cnf file (e.g. using character-set-server = utf8mb4 collation-server = utf8mb4_bin)

you can also export these requests to a file for convenience, for example:

SELECT CONCAT('ALTER TABLE `', table_name, '` MODIFY `', column_name, '` ', DATA_TYPE, ' CHARACTER SET <charset> COLLATE <collation>', (CASE WHEN IS_NULLABLE = 'NO' THEN ' NOT NULL' ELSE '' END), ';')
FROM information_schema.COLUMNS 
WHERE TABLE_SCHEMA = '<yourDB>'
AND DATA_TYPE != 'varchar'
AND
(
    CHARACTER_SET_NAME != '<charset>'
    OR
    COLLATION_NAME != '<collation>'
)
INTO OUTFILE '/tmp/modify-columns.sql'

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