引言

I know, we can not rename a column using modify column syntax,but can change column syntax.

My question is: what is the main usage of modify syntax?

For example,

alter table tablename change col1 col1 int(10) not null

instead of

alter table tablename modify col1 int(10) not null

Edited

Question replaced

What is the main usage of modify syntax?

Above question was replaced by below

Why we have to use change column instead of modify column?

解释

CHANGE COLUMN If you have already created your MySQL database, and decide after the fact that one of your columns is named incorrectly, you don’t need to remove it and make a replacement, you can simply rename it using change column.

ALTER TABLE MyTable CHANGE COLUMN foo bar VARCHAR(32) NOT NULL FIRST;

MODIFY COLUMN This command does everything CHANGE COLUMN can, but without renaming the column.You can use the modify SQL command if you need to resize a column in MySQL. By doing this you can allow more or less characters than before. You can’t rename a column using modify and other

ALTER TABLE MyTable MODIFY COLUMN foo VARCHAR(32) NOT NULL AFTER baz;

Note : ALTER TABLE is used for altering a table means to change column name, size, drop column. CHANGE COLUMN and MODIFY COLUMN commands cannot be used without help of ALTER TABLE command.

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