Subqueries inside WHERE and SELECT

Joining Data in SQL

Maham Faisal Khan

Senior Content Developer, DataCamp

Syntax for subqueries inside WHERE

  • All semi joins and anti joins we have seen included a subequery in WHERE
  • WHERE is the most common place for subqueries

Syntax for query using WHERE IN statement

SELECT *
FROM some_table
WHERE some_numeric_field IN (4, 8, 12);
Joining Data in SQL

Syntax for subqueries inside WHERE

SELECT *
FROM some_table
WHERE some_field IN 
       (include subquery here);
Joining Data in SQL

Syntax for subqueries inside WHERE

SELECT *
FROM some_table
WHERE some_field IN 
    (SELECT some_numeric_field
     FROM another_table
     WHERE field2 = some_condition);
Joining Data in SQL

Subqueries inside SELECT

SELECT DISTINCT continent
FROM states;

|---------------|
| continent     |
|---------------|
| Africa        |
| Asia          |
| Europe        |
| North America |
| Oceania       |
|---------------|
Joining Data in SQL

Subqueries inside SELECT

SELECT DISTINCT continent,

    (SELECT COUNT(*)
     FROM monarchs

     WHERE states.continent = monarch.continent) AS monarch_count
FROM states;

| continent     |   monarch_count |
|---------------|-----------------|
| Africa        |               0 |
| Asia          |               2 |
| Europe        |               2 |
| North America |               0 |
| Oceania       |               0 |
Joining Data in SQL

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Joining Data in SQL

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