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 shortcut menu, and then select Query Builder.
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 shortcut menu.
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 shortcut menu. You can also remove a join by clicking this button.
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.
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.
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.
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.
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. Also, you can watch this video tutorial:
