DB Normalised#163
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Review Summary
I am requesting changes because the current task.sql cannot be executed successfully and does not fully meet the specified requirements.
Critical issues that must be fixed:
- At the very top of
task.sql, beforeCREATE DATABASE ShopDB;, you need to add a statement to remove any existing database, e.g.DROP DATABASE IF EXISTS ShopDB;(the task explicitly requires droppingShopDBbefore recreating it). - The table creation order currently causes a foreign key error:
ProductInventoryis created while referencingWarehouses(and possiblyProducts) before those tables exist, which leads toERROR 1824 (HY000). Reorder your DDL so thatCountriesis created first, thenProducts, thenWarehouses, and only thenProductInventorywith its foreign keys. - Your two
INSERT INTO ProductInventory ...statements referenceProductID = 1andWarehouseID = 1and2, but there are no corresponding rows inProductsandWarehouses. Before inserting intoProductInventory, addINSERTstatements for at least one product withProductID = 1and for warehouses withWarehouseID = 1and2, usingCountryIDvalues that match existingCountriesrows (e.g.1and2).
As minor improvements (not blockers), consider enforcing NOT NULL on required columns, using DECIMAL for prices, and optionally making (ProductID, WarehouseID) unique or the primary key in ProductInventory to prevent duplicate inventory records. Overall, your normalization approach (separate Products, Warehouses, Countries, and ProductInventory) is on the right track; once these execution and data integrity issues are fixed, the script will align well with the task requirements.
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Footnotes
| FOREIGN KEY (ProductID) REFERENCES Products(ID) ON DELETE NO ACTION, | ||
| PRIMARY KEY (ID) | ||
| ); | ||
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The script is missing a DROP DATABASE ShopDB; statement before creating the database (the task explicitly asks to remove any existing ShopDB using DROP DATABASE ShopDB;). Add this at the top before CREATE DATABASE to match the requirements.
| Name VARCHAR(50), | ||
| Description VARCHAR(100), | ||
| Price INT, | ||
| PRIMARY KEY (ID) |
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Products table is defined but there are no INSERT statements for Products. The ProductInventory rows reference ProductID = 1, so you must insert a matching product (e.g., ID = 1 with name/description/price) before inserting into ProductInventory.
| CREATE TABLE Warehouses ( | ||
| ID INT, | ||
| Name VARCHAR(50), | ||
| Address VARCHAR(50), | ||
| CountryID INT, | ||
| FOREIGN KEY (CountryID) REFERENCES Countries(ID) ON DELETE NO ACTION, | ||
| FOREIGN KEY (CountryID) REFERENCES Countries(ID) ON DELETE NO ACTION, |
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Warehouses table exists but there are no INSERT statements for Warehouses. ProductInventory references WarehouseID = 1 and 2, so add INSERTs for warehouses with IDs 1 and 2 (including Address and CountryID matching the Countries rows) before inserting product inventory.
| INSERT INTO ProductInventory (ID,ProductID,WarehouseAmount,WarehouseID) | ||
| VALUES (1, 1, 2, 1); | ||
| INSERT INTO ProductInventory (ID,ProductID,WarehouseAmount,WarehouseID) | ||
| VALUES (2, 1, 5, 2); |
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The two INSERT INTO ProductInventory (...) VALUES (...) statements will fail due to missing referenced Products and Warehouses rows. Ensure referenced Products and Warehouses are inserted first (or insert ProductInventory after those INSERTs). Also confirm the inserted warehouse CountryID values reference existing Countries (IDs 1 and 2).
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Review Summary
I am requesting changes because one explicit checklist requirement about table creation order is not yet met, even though the schema itself is largely correct and runs. In task.sql, the CREATE TABLE Warehouses block currently appears before the CREATE TABLE Products block; you need to reorder the DDL so the sequence is exactly Countries -> Products -> Warehouses -> ProductInventory as required by the task ([CHECKLIST ITEM #13]). This ordering requirement is important because the automated grader and checklist expect that precise order, so leaving it as-is may cause your solution to be flagged even though the foreign keys work.
In addition to that required fix, there are a few recommended improvements to strengthen your schema (these are not blockers, but strongly encouraged): change Products.Price from INT to a money-safe type like DECIMAL(10,2) NOT NULL, add NOT NULL AUTO_INCREMENT to integer primary key columns such as Products.ID and Warehouses.ID, and enforce uniqueness of (ProductID, WarehouseID) in ProductInventory (either as a composite primary key or a UNIQUE constraint) to prevent duplicate inventory rows. After reordering the CREATE TABLE statements and, if you choose, applying these enhancements, rerun your script followed by the provided test.sql to confirm everything passes. Overall, you’re very close—once you fix the DDL order, your solution should satisfy the core requirements.
✨ Please rate this review in the Platform's notification center1. I will be grateful for your feedback! ✨
Important
Fix the issues, commit the changes, and then re-request my review using the Re-request review button2 in the Reviewers tab.
Tip
If you have any comments about this review, please leave a message in the Add a comment section below and mention me with the @mateacademy-ai-mentor tag3.
I will read your message during my next review of your pull request. Please do not reply directly to my comments, as that feature is not supported yet.
Caution
Do not close the pull request until the review is complete. Closing it early can lead to unexpected behavior and disrupt the review process.
Footnotes
| PRIMARY KEY (ID) | ||
| ); | ||
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| CREATE TABLE Warehouses ( |
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The task (and the previous review) requires the DDL be ordered Countries -> Products -> Warehouses -> ProductInventory. Here Warehouses is created before Products which violates that requested order and may be flagged by the grader. Move the Products CREATE TABLE block so it appears before the Warehouses CREATE TABLE block.
| ID INT, | ||
| Name VARCHAR(50), | ||
| Description VARCHAR(100), | ||
| Price INT, |
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Price is currently declared as INT. For monetary values use a decimal type (for example DECIMAL(10,2)) and consider adding NOT NULL to enforce presence of a price.
| CREATE TABLE ProductInventory ( | ||
| ID INT, | ||
| ProductName VARCHAR(50), | ||
| ProductID INT, |
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ProductInventory uses a surrogate ID as primary key (ID). To prevent duplicate inventory rows and better model the relationship, consider making (ProductID, WarehouseID) the primary key or at least a UNIQUE constraint on those two columns.
| ); | ||
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| CREATE TABLE Products ( | ||
| ID INT, |
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Primary key ID columns (e.g. Products.ID) are declared without NOT NULL or AUTO_INCREMENT. Consider adding NOT NULL and AUTO_INCREMENT to primary key integer columns to ensure uniqueness and simplify inserts (optional but recommended).
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Review Summary
Your solution is approved as an educational override to help you keep progressing while you continue learning, even though there are a few things to refine.
You did a solid job normalizing the schema into Countries, Products, Warehouses, and ProductInventory, and you correctly create the database ShopDB, drop it if it exists, and follow the required creation order so that all foreign keys can be resolved.
One improvement area is in the Products table (around the Price column definition, e.g., near line 25): using INT for prices can cause problems for money values, so consider switching to something like DECIMAL(10,2) so you can represent cents accurately.
In the ProductInventory table (around the column list and constraints, e.g., lines 45–55), you currently allow multiple rows for the same (ProductID, WarehouseID) pair; adding a UNIQUE (ProductID, WarehouseID) constraint or using these two columns as a composite primary key would prevent duplicate inventory records.
Also, for your primary key columns (e.g., ID in each table, around lines 10–12, 22–24, 34–36, and 46–48), consider declaring them as INT NOT NULL AUTO_INCREMENT so MySQL handles ID assignment automatically and you clearly express that these columns cannot be null.
These changes are not blocking for this task, but they will make your design more robust and closer to production-ready SQL.
Overall, this is a strong submission that meets the core requirements, and with a few datatype and constraint tweaks in a future revision, your database design skills will be even stronger.
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