Course Content
Introduction to SQL
Introduction to SQL
Checking for NO Value
When a column doesn't have any value, it's regarded as having a NULL
value. To identify whether a value is NULL
, we check if it's equal to NULL
. Alternatively, the SELECT
statement provides a WHERE
clause and an IS NULL
clause, which is used to examine columns with NULL
values.
Let's illustrate this with an example:
SELECT name FROM country WHERE region IS NULL;
Task
Write an SQL query that returns the name
and capital
columns with no population.
Here's a short example of the country
table:
id | name | continent | region | surfacearea | capital | population |
1 | Japan | Asia | Eastern Asia | 377829 | Tokyo | 126714000 |
2 | Latvia | Europe | NULL | 64589 | Riga | 2424200 |
3 | Mexico | North America | Central America | 1958201 | Mexico City | 98881000 |
... | ... | ... | ... | ... | ... | ... |
15 | Malta | Europe | Southern Europe | 316 | Valletta | 380200 |
Task
Write an SQL query that returns the name
and capital
columns with no population.
Here's a short example of the country
table:
id | name | continent | region | surfacearea | capital | population |
1 | Japan | Asia | Eastern Asia | 377829 | Tokyo | 126714000 |
2 | Latvia | Europe | NULL | 64589 | Riga | 2424200 |
3 | Mexico | North America | Central America | 1958201 | Mexico City | 98881000 |
... | ... | ... | ... | ... | ... | ... |
15 | Malta | Europe | Southern Europe | 316 | Valletta | 380200 |
Everything was clear?
Checking for NO Value
When a column doesn't have any value, it's regarded as having a NULL
value. To identify whether a value is NULL
, we check if it's equal to NULL
. Alternatively, the SELECT
statement provides a WHERE
clause and an IS NULL
clause, which is used to examine columns with NULL
values.
Let's illustrate this with an example:
SELECT name FROM country WHERE region IS NULL;
Task
Write an SQL query that returns the name
and capital
columns with no population.
Here's a short example of the country
table:
id | name | continent | region | surfacearea | capital | population |
1 | Japan | Asia | Eastern Asia | 377829 | Tokyo | 126714000 |
2 | Latvia | Europe | NULL | 64589 | Riga | 2424200 |
3 | Mexico | North America | Central America | 1958201 | Mexico City | 98881000 |
... | ... | ... | ... | ... | ... | ... |
15 | Malta | Europe | Southern Europe | 316 | Valletta | 380200 |
Task
Write an SQL query that returns the name
and capital
columns with no population.
Here's a short example of the country
table:
id | name | continent | region | surfacearea | capital | population |
1 | Japan | Asia | Eastern Asia | 377829 | Tokyo | 126714000 |
2 | Latvia | Europe | NULL | 64589 | Riga | 2424200 |
3 | Mexico | North America | Central America | 1958201 | Mexico City | 98881000 |
... | ... | ... | ... | ... | ... | ... |
15 | Malta | Europe | Southern Europe | 316 | Valletta | 380200 |
Everything was clear?
Checking for NO Value
When a column doesn't have any value, it's regarded as having a NULL
value. To identify whether a value is NULL
, we check if it's equal to NULL
. Alternatively, the SELECT
statement provides a WHERE
clause and an IS NULL
clause, which is used to examine columns with NULL
values.
Let's illustrate this with an example:
SELECT name FROM country WHERE region IS NULL;
Task
Write an SQL query that returns the name
and capital
columns with no population.
Here's a short example of the country
table:
id | name | continent | region | surfacearea | capital | population |
1 | Japan | Asia | Eastern Asia | 377829 | Tokyo | 126714000 |
2 | Latvia | Europe | NULL | 64589 | Riga | 2424200 |
3 | Mexico | North America | Central America | 1958201 | Mexico City | 98881000 |
... | ... | ... | ... | ... | ... | ... |
15 | Malta | Europe | Southern Europe | 316 | Valletta | 380200 |
Task
Write an SQL query that returns the name
and capital
columns with no population.
Here's a short example of the country
table:
id | name | continent | region | surfacearea | capital | population |
1 | Japan | Asia | Eastern Asia | 377829 | Tokyo | 126714000 |
2 | Latvia | Europe | NULL | 64589 | Riga | 2424200 |
3 | Mexico | North America | Central America | 1958201 | Mexico City | 98881000 |
... | ... | ... | ... | ... | ... | ... |
15 | Malta | Europe | Southern Europe | 316 | Valletta | 380200 |
Everything was clear?
When a column doesn't have any value, it's regarded as having a NULL
value. To identify whether a value is NULL
, we check if it's equal to NULL
. Alternatively, the SELECT
statement provides a WHERE
clause and an IS NULL
clause, which is used to examine columns with NULL
values.
Let's illustrate this with an example:
SELECT name FROM country WHERE region IS NULL;
Task
Write an SQL query that returns the name
and capital
columns with no population.
Here's a short example of the country
table:
id | name | continent | region | surfacearea | capital | population |
1 | Japan | Asia | Eastern Asia | 377829 | Tokyo | 126714000 |
2 | Latvia | Europe | NULL | 64589 | Riga | 2424200 |
3 | Mexico | North America | Central America | 1958201 | Mexico City | 98881000 |
... | ... | ... | ... | ... | ... | ... |
15 | Malta | Europe | Southern Europe | 316 | Valletta | 380200 |