[Concept Class] Learn and Use SQL Queries Right Away
You will be able to extract the data you want directly without the help of a developer. We will provide everything you need for analysis, from simple queries to joins. Start learning SQL with a direct lecture from the author of the book <Planner's SQL>.
Q. I need to query a DB I have never seen before. Is there a standard for understanding the data?
Q. I need to query a DB I have never seen before. Is there a standard for understanding the data?
- As in the lecture, you need to check the data by sampling only some of the data by setting a limit or using top, etc.
- But this alone is often not enough. Even when looking at sample data, there are times when it is unclear what the data is.
- The conditions that determine what data are 1) schema and 2) row occurrence rules .
- A schema is a blueprint for the table structure, including what columns there are and what data types the columns allow.
- A row occurrence rule refers to the rule for when a data row occurs in the table and when the trigger occurs.
- This is something that everyone who has ever run a query up to the schema has kept in mind.
- Surprisingly, it is easy to miss what the rules for occurrence are. These are usually determined by the backend server.
- For example, in the case of an order table, normally one row may be created when one order occurs.
- When an order is cancelled, it is necessary to clearly understand the rules for whether the existing order row is modified or a new row is created.
- These rules may be somewhat difficult to verify because they are part of the backend developer developing WAS or analyzing the backend source code.
- Since it is a very important part that determines the format of the data, it is important to know it when looking at a new DB for reliable analysis, right? :-)
* This is a new post where we share answers to frequently asked questions about SQL.