In this tutorial, we will learn about Scalar Subquery with an example. Scalar subquery is the simplest form
of a subquery. Scalar subquery as the name suggests is a subquery that returns a scalar or single value.
To know the scalar subquery placement in the SQL statement:
In this example, we will use the City table from the world MySQL table. The following example shows how to use a scalar subquery as part of a WHERE clause conditions.
mysql> SELECT Name FROM City
-> WHERE Population >
-> (SELECT Population FROM City WHERE Name= ‘New York’);
| Name |
| SÃ£o Paulo |
| Jakarta |
| Mumbai (Bombay) |
| Shanghai |
| Seoul |
| Ciudad de MÃ©xico |
| Karachi |
| Istanbul |
| Moscow |
9 rows in set (0.03 sec)
If we execute the subquery from the above example as a stand-alone statement, we will notice that the query yields a scalar/single value.
mysql> SELECT Population FROM City WHERE Name= ‘New York’;
| Population |
| 8009000 |
1 row in set (0.00 sec)
Scalar subqueries can appear almost anywhere that a scalar value is allowed by the SQL syntax.
This means that you can use subqueries as function parameters, use mathematical operators on subqueries
that evaluate to numeric values, etc.
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