SQL¶

ALTER TABLE¶

ALTER TABLE testing
ADD COLUMN test_age INTEGER;

Remove a column

ALTER TABLE testing
DROP COLUMN test_age;

SELECT¶

If hero is a table, then below command can be used to select hero_age column from it.

SELECT hero_age from hero;

OR

SELECT hero.hero_age from hero;

To select distinct items from a column,

SELECT DISTINCT hero_age from hero;

Interview Questions¶

Difference between where and having

Both the clauses are used to apply conditions on data. Where is used to applu conditions on a table like data, on the other hand Having is used to apply conditoins on data returned by aggregate functions like count(), avg(), max(), min() etc... These functions return a scalar value and not set of values(table like structure).