Practical SQL, 2nd Edition: A Beginner's Guide to Storytelling with Data

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Here, WX is the only candidate key and there is no partial dependency, i.e., any proper subset of WX doesn’t determine any non-prime attribute in the relation. This hands-on SQL course is a set of over 150 interactive exercises based on a database of students and lecturers. Need to practice writing SQL queries? This is for you! Range Partitioning: This method is done by partitioning based on a range of values. This method is most commonly used upon date fields to get monthly, weekly or yearly data. In the case of corner cases like value belonging to the end of the range, for example: if the range of partition 1 is 10-20 and the range of partition 2 is 20-30, and the given value is 10, then 10 belongs to the second partition and not the first. AND T.WORKER_TITLE in ('Manager'); Q-25. Write an SQL query to fetch duplicate records having matching data in some fields of a table.

Learning SQL, of course, is no different. You cannot expect to become proficient at SQL unless you hop onto a database and start practicing it. Note: Any non-aggregated column appearing in SELECT must also appear in GROUP BY . But this is logical – the whole purpose is to group data by department, so of course we’ll put it in GROUP BY. Output department You can read about the history of SQL in the article How It All Began by Agnieszka Kozubek-Krycuń. SQL is over 50 years old and it’s not going anywhere! Phantom reads: This occurs when two same queries when executed separately return different rows. For example, if transaction A retrieves some set of rows matching search criteria. Assume another transaction B retrieves new rows in addition to the rows obtained earlier for the same search criteria. The results are different.Now, that you should have a solid foundation in intermediate SQL, let’s take a look at some more advanced SQL query questions. These questions will require us to use more complex SQL syntax and concepts, such as nested queries, joins, unions, and intersects. Q-33. Write an SQL query to determine the nth (say n=5) highest salary from a table.

Many-to-Many - This is used in cases when multiple instances on both sides are needed for defining a relationship. So we’ll use these columns in ON, but we also need to specify which table each column is from. Remember, we gave our tables aliases. This will come in handy here, as we won’t need to write the tables’ full names – only one letter for each table. We write the first table’s alias (instead of its full name), separate them with a dot, and then the column name. We put the equal sign, the second table’s alias, and the column name.It has a sample database feature, which shows AdventureWorks for SQL Server, and there are many other SQL versions supported: The required query is: Select distinct length(DEPARTMENT) from Worker; Q-9. Write an SQL query to print the FIRST_NAME from the Worker table after replacing ‘a’ with ‘A’. ALTER TABLE Students /* Set multiple columns as unique */ ADD CONSTRAINT PK_Student /* Naming a unique constraint */ UNIQUE (ID, FirstName); 10. What is a Foreign Key?