| Clause |
Type |
Query |
Meaning |
|---|
| Select |
all columns |
select * from actor; |
display all columns from table actor |
| Select |
specific columns |
select first_name,last_name from actor; |
display only first_name and last_name columns from table actor |
| Order By |
descending ordering |
select first_name,last_name from actor
order by first_name desc; |
sort the selected columns by first_name in descending order Z-A |
| Order By |
ascending ordering
default |
select first_name,last_name from actor
order by first_name asc; |
sort the selected columns by last_name in ascending order A-Z |
| Order By |
multiple column ordering |
select * from payment
order by customer_id asc, amount desc; |
first sorts result by customer_id in ascending – if multiple customer_id rows are present then sorts them by amount in descending |
| Distinct |
single column |
select distinct rating from film; |
distinct will give unique values in a column – will show all distinct rating values in the rating column |
| Distinct |
multiple column |
select distinct rating,rental_duration from film
order by rating; |
distinct will apply on both columns – will return unique combinations of both columns – rating and duration |
| Limit |
|
select * from rental
order by rental_date desc limit 5; |
returns only top x rows – used with order by to return top x results |
| Count |
with * |
select count(*) from customer; |
Counts the number of rows in the table – customer |
| Count |
with column |
select count(first_name) from customer; |
Counts the number of rows in the column – first_name
Nulls will not be counted |
| Count |
with distinct |
select count(distinct first_name) from customer; |
Counts the number of distinct values in the column |
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