After setting up my first small databases the next learning steps concern basic operation on existing tables in a MySQL database, such as deleting or creating additional variables/columns in a table. I found tech-recipes.com very helpful:
Delete a variable/column
To delete the column MyCol from the table MyTable, use the following SQL command:
ALTER TABLE MyTable DROP MyCol
Comment: Tech-Recipes.com used single-quotes around MyCol and MyTable which I found not necessary.
Add a column/variable
To add a column called email [...] with a datatype of VARCHAR(60) to the table contacts, use the following SQL statement:
ALTER TABLE contacts ADD email VARCHAR(60);This first statement will add the email column to the end of the table. To insert the new column after a specific column, such as name, use this statement:
ALTER TABLE contacts ADD email VARCHAR(60) AFTER name;If you want the new column to be first, use this statement:
ALTER TABLE contacts ADD email VARCHAR(60) FIRST;
Update/Change the values in a column
One would use the UPDATE statement so I looked it up in the reference
UPDATE [LOW_PRIORITY] [IGNORE] table_reference
SET col_name1={expr1|DEFAULT} [, col_name2={expr2|DEFAULT}] ...
[WHERE where_condition]
[ORDER BY ...]
[LIMIT row_count]
In order to update the column intensity in the table measures from “20%” to simply “20″ one would
UPDATE measures SET intensity="20" WHERE intensity="20%";
