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Intermediate SQL
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Kursusindhold

Intermediate SQL

Intermediate SQL

1. Grouping
GROUP BY ClauseOrder of StatementsChallenge: Total Ride Time for Each Subway LineAverage Student's Grade ChallengeSearching for the Top Math Students ChallengeHAVING ClauseSeveral Aggregate Functions in the QueryMore Complex Filtering
2. Nested Subqueries
Nested QueriesChallenge: Non-tech Department EmployeesUsing Inner Subqueries in the FROM SectionChallenge: Employees With More Than Average SalaryUNION ClauseChallenge: Combining Table Results
3. Joining Tables
JOIN 2 TablesChallenge: Get Category By Product PriceChallenge: Get Minimum Price By CategoryChallenge: Get Product Amount By CategoryLEFT, RIGHT and INNER JOINsChallenge: Table JoinChallenge: FULL JOIN Usage
4. DDL and DML in SQL
CREATE and ConstraintsALTER and INSERT OperationsDROP and TRUNCATEUPDATE and DELETE

book
Using Inner Subqueries in the FROM Section

An inner subquery creates a table with which we then perform operations in the outer query.

From this, we can conclude that we can also use an inner query within the FROM section to select something from this table.

Let's consider an example where we need to work with employees whose salary is above a certain value. But instead of a WHERE clause, we will use an inner query:


              
123456

            
SELECT *
FROM (
  SELECT * 
  From employees
  WHERE salary >= 70000
) AS high_salary_employees
copy

We've created a new table using an inner subquery with which we can work and gather information.

Note

Notice that for such a table, it's essential to provide an alias.

When might this be useful?

Such a query is highly readable; sometimes, it can replace a WHERE clause.

Additionally, if you need to work not with the entire table but only with a filtered part, an inner subquery within the FROM section can be extremely handy.

Opgave

Swipe to start coding

Your task is to retrieve the average budget (budget column) for all managerial departments from the department table. Use an inner subquery in the FROM section to filter only the managerial type of department. Also, use the alias manager_departments for this table so the task is checked correctly.

The response should have only one column, average_budget. This is an alias for the aggregate function AVG().

Note

This task could also be done using a WHERE clause, but we use a nested query here to practice this syntax, which will be useful for solving more complex problems in the future.

Brief Instructions

  • Retrieve the average value of the budget column.
  • Assign the alias average_budget to that column.
  • In the FROM clause, you need to write a nested query.
  • In the nested query, select all columns from the department table.
  • In the nested query, use the WHERE clause with the condition type = 'manager'.
  • Assign the alias manager_departments to the nested query.

Løsning

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Sektion 2. Kapitel 3
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book
Using Inner Subqueries in the FROM Section

An inner subquery creates a table with which we then perform operations in the outer query.

From this, we can conclude that we can also use an inner query within the FROM section to select something from this table.

Let's consider an example where we need to work with employees whose salary is above a certain value. But instead of a WHERE clause, we will use an inner query:


              
123456

            
SELECT *
FROM (
  SELECT * 
  From employees
  WHERE salary >= 70000
) AS high_salary_employees
copy

We've created a new table using an inner subquery with which we can work and gather information.

Note

Notice that for such a table, it's essential to provide an alias.

When might this be useful?

Such a query is highly readable; sometimes, it can replace a WHERE clause.

Additionally, if you need to work not with the entire table but only with a filtered part, an inner subquery within the FROM section can be extremely handy.

Opgave

Swipe to start coding

Your task is to retrieve the average budget (budget column) for all managerial departments from the department table. Use an inner subquery in the FROM section to filter only the managerial type of department. Also, use the alias manager_departments for this table so the task is checked correctly.

The response should have only one column, average_budget. This is an alias for the aggregate function AVG().

Note

This task could also be done using a WHERE clause, but we use a nested query here to practice this syntax, which will be useful for solving more complex problems in the future.

Brief Instructions

  • Retrieve the average value of the budget column.
  • Assign the alias average_budget to that column.
  • In the FROM clause, you need to write a nested query.
  • In the nested query, select all columns from the department table.
  • In the nested query, use the WHERE clause with the condition type = 'manager'.
  • Assign the alias manager_departments to the nested query.

Løsning

Switch to desktopSkift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder
Var alt klart?

Hvordan kan vi forbedre det?

Tak for dine kommentarer!

Sektion 2. Kapitel 3
Switch to desktopSkift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder
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