What is the difference between CHAR_LENGTH and LENGTH?

The first is character count. The second is byte count. For the Latin characters the numbers are the same, but they’re not the same for Unicode and other encoding.

How do you get a portion of a string?

Using SUBSTR you can get a portion of a string.

Example :
SELECT SUBSTR(column_name, 1, 10) from table_name;

How do you concatenate strings in MySQL?

Using CONCAT method you can concatenate strings in MySQL.

Example :
CONCAT (string1, string2, string3)

How do I find out all databases starting with ‘mysql’ to which I have access to?

Using following query you can find out all databases starting with “mysql”.

SHOW DATABASES LIKE ‘mysql%’;

How would you change a table to InnoDB?

You can change a table to InnoDB using following query.

ALTER TABLE table_name ENGINE innodb;

How would you delete a column?

You can delete a column using following query.

ALTER TABLE table_name DROP column_name;

How would you change a column from VARCHAR(30) to VARCHAR(100)?

ALTER TABLE table_name CHANGE column_name column_name VARCHAR(100).