How to write complex MySQL queries?

March 26th, 2020

Advanced queries aimed to solve complex tasks or multiple tasks constitute an essential part of any database administrator or developer job. MySQL complex queries must be handled with the utmost seriousness since inaccurate MySQL code or poorly performing scripts can cause severe bugs and application failures. 

What is a complex MySQL query?

Complex MySQL queries search data using more than one parameter and may comprise a combination of several joins across multiple tables and quite a few nested subqueries (queries nested within another query). Complex queries also frequently involve heavy use of AND and OR clauses.

Complex queries are typically used to retrieve complex data from multiple tables. Advanced queries can also be used for reporting, joining multiple tables, nesting queries, and transaction locking.

Complex MySQL query with multiple SELECT statements

For analytical purposes, it’s often necessary to fetch data from several different tables to form a single result table. Thus, complex MySQL queries with multiple SELECT statements are the most common advanced queries used by DBAs and developers. When you combine the results of multiple SELECT statements, you can choose what to include in the result table. This is exactly what makes them so popular.

Example of how to build complex MySQL queries in dbForge Studio for MySQL

Writing advanced queries can be intimidating and somewhat confusing to a MySQL novice. That’s where dbForge Studio for MySQL comes into help. Its cutting-edge Query Builder functionality comprises an easy-to-learn-and-operate visual query designer that lets you create MySQL queries without manual coding.

Step 1. Enabling Query Builder

To start working with Query Builder, select it from the SQL Development tools list on the Start page of the Studio.

Step 2. Adding tables to the query

To add tables and views to the query, simply drag-and-drop them from the Database Explorer tree to the query diagram. Alternatively, you can right-click the required tables in the Database Explorer, click the Send To command from the context menu and then select Query Builder.

Adding tables to the query

Step 3. Creating subqueries

dbForge Studio offers full support for subqueries in all SELECT statement clauses. Each subquery can have its own subqueries. When you create a subquery or open it for visual editing, a subquery tab of the query document appears. Using these tabs, you can easily navigate between subqueries.

To create a subquery, right-click the diagram body and select Create Subquery command from the context menu.

Creating subqueries

Step 4. Creating JOINs between the tables

dbForge Studio for MySQL allows you to visually create the following JOINs: INNER, LEFT OUTER, RIGHT OUTER, NATURAL, and CROSS JOIN. You can also easily set quite complex conditions for a join of any kind.

Joins are automatically created when a table with a foreign key and its referenced table are placed on the diagram. To add a join, navigate to the Joins tab of the tabbed editor and click the Add button on the top of the tree node. A new empty join with an empty condition will appear. Click the Enter table name field and specify the join tables. Then set the type of the join by clicking the red-colored text link and selecting a required item from the context menu. You can also remove a join by clicking this button.

Creating JOINS

Step 5. Building WHERE or HAVING clauses if necessary

When retrieving data, you may need to filter or exclude the records. And the best way to achieve that is to use WHERE and HAVING clauses. 

To build WHERE and\or HAVING clauses, navigate to the corresponding tabs and make the necessary adjustments using the intuitive interface.

Creating WHERE and\or HAVING clause

Step 6. Creating GROUP BY or ORDER BY clauses

GROUP BY and ORDER BY clauses are used to organize the output data. To create those clauses, navigate to the relevant tab and select columns for sorting.

Creating GROUP BY or ORDER BY clauses

Step 7. Viewing and executing the query

After you’ve made all the necessary adjustments switch to the Text view to inspect the automatically generated query. If you’re satisfied with the result, click the Execute button on the main toolbar to run the script.

Viewing and executing the query

Step 8. Analyzing the result

The query result will be displayed immediately for you to analyze. The Data Editor functionality built into dbForge Studio for MySQL allows manipulating data in the most convenient way.

Query result

Conclusion

When it comes to building complex MySQL queries, working with subqueries, clauses and conditions might seem to be strenuous especially for beginners. The Query Builder functionality that comes with dbForge Studio for MySQL is bound to take away that pain. Intuitive and well-designed GUI significantly simplifies building complex queries and managing JOIN conditions.

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