You should see this output: Database changed Switch to the test_db database: USE test_db You should see this output, which confirms that the database was created successfully: Query OK, 1 row affected (0.01 sec) To create a sample database named test_db, run: CREATE DATABASE test_db If you are using MariaDB, you may see a prompt like the following instead: MariaDB > Note that your MySQL server’s root password is not the same as the root password for your Linode. When prompted, enter the root password of your MySQL server and hit Enter to continue. SSH to your server and log in to MySQL as root: mysql -u root -p This sample database is used to run the different example queries in this guide: To understand how subqueries work, create a sample database first. Please refer to the MySQL section, which contains guides that describe how to install MySQL on several Linux distributions. The MySQL server software (or MariaDB) installed on your Linode. You may also wish to set the timezone, configure your hostname, create a limited user account, and harden SSH access. See our Getting Started with Linode and Creating a Compute Instance guides.įollow our Setting Up and Securing a Compute Instance guide to update your system. If you have not already done so, create a Linode account and Compute Instance. To follow along with this guide, make sure you have the following: How to use a subquery as a derived table.How to use a correlated subquery in a comparison operator.They help developers code business logic into the MySQL queries.They are used to enforce referential integrity in a scenario where foreign keys are not implemented.They eliminate the need for using complex UNION statements and JOIN statements.In other words, subqueries help isolate complex parts of queries. They break the SQL statements into simple logical units, which can make them easier to understand and maintain.When building MySQL applications, using subqueries offers several advantages: When subqueries are executed, the subquery is processed first before the parent query. Subqueries can be applied in SELECT, INSERT, UPDATE, and DELETE operations. Subqueries are used to pre-process data that is used in the parent query. The command that the subquery is nested in is referred to as the parent query. A subquery is an SQL (Structured Query Language) query that is nested within another SQL query. What would you like the result to look like?Īlthough you never actually confirmed your expected output, this is what I think you want Your two records have values 1 and 3.īecause you LIMIT 1 in the subquery it's going to give only one record, which matches the "1" | product_location_id | transaction_date | current_inventory |Īdding pl.id to your query's field list illustrates it. | productName | productCode | current_inventory | transaction_date | name | id | The key to your problem lies in that join between your other tables and the subquery Can somebody kick me in the head to knock the dust loose and help me figure this out? Note that I'm not getting a value for either current_inventory or transaction_date for product S10_1949, despite there being 3 matched rows in product_inventory. This is a historical inventory query - the data is as follows: I've been beating my forehead against this for a few hours now and though I'm sure it's something incredibly obvious and simple, I'm just not seeing the error.
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