MySQL: How to alter varchar(255) UNIQUE column to UNIQUE Text NOT NULL?

Question

The current column is a VARCHAR(255) NOT NULL, so how do I change it to TEXT NOT NULL?

NOTE: The column intended to be changed its property type is a UNIQUE KEY comb

Answer 1

alter table your_table
modify column your_column text not null;

for unique key

alter table your_table 
add unique index your_index_name (your_column(your_length));

your_length = allow up 1000 bytes

The maximum key length is 1000 bytes. This can also be changed by changing the source and recompiling. For the case of a key longer than 250 bytes, a larger key block size than the default of 1024 bytes is used

---

Both length (description + another column can not longer than 1000),so

alter table your_table 
add unique index your_index_name (description(800), another_column(200));