A FOREIGN KEY comprises of single or collection of fields in a table that essentially refers to the PRIMARY KEY in another table. Foreign key constraint ensures referential integrity in the relation between two tables. One of the most interesting books about SQL I've ever read. At first glance, it looks like a guide for complete rookies. But the author raises topics that will interest advanced users." 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 Clustered index is used for easy and speedy retrieval of data from the database, whereas, fetching records from the non-clustered index is relatively slower.

Clustered index modifies the way records are stored in a database based on the indexed column. A non-clustered index creates a separate entity within the table which references the original table.The required query is: SELECT * FROM Worker WHERE MOD (WORKER_ID, 2) = 0; Q-28. Write an SQL query to clone a new table from another table. The required query is: Select * from Worker where FIRST_NAME like '%a'; Q-18. Write an SQL query to print details of the Workers whose FIRST_NAME ends with ‘h’ and contains six alphabets. It offers practice queries and interactive SQL engines, so don’t overlook SQLZOO for some great steps forward in your SQL-learning journey. 4. Oracle LiveSQL However, we want to show only employees whose name is Luca. For this, we again use WHERE. The approach is similar to the previous example: we use WHERE, write the column name, and use the comparison operator. This time, our condition uses the equal sign ( =). SELECT operator in SQL is used to select data from a database. The data returned is stored in a result table, called the result-set. SELECT * FROM myDB.students; 20. What are some common clauses used with SELECT query in SQL?

The required query is: Select * from Worker where SALARY between 100000 and 500000; Q-20. Write an SQL query to print details of the Workers who joined in Feb 2021. The other table in the dataset is named quarterly_sales. It is shown below, and the query for creating it is here. employee_id In general, this table is a list of each quarter’s sales made by every employee shown in the first table.

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In addition, for your work, you will receive a special certificate that you will be able to show your boss and join to your LinkedIn profile. Perhaps this is the chance to achieve the raise that you've been eyeing for months? Or maybe a future employer will notice you on social media and offer you a good position? Conclusion The output shows the departments and the lowest salary in each department. 15. Using MAX() and GROUP BY

INNER) JOIN: Retrieves records that have matching values in both tables involved in the join. This is the widely used join for queries. The required query is: Select * from Worker where FIRST_NAME in ('Vipul','Satish'); Q-14. Write an SQL query to print details of workers excluding first names, “Vipul” and “Satish” from the Worker table. Each exercise includes a sample database with ERD, a question to solve, and an editor that lets you enter SQL and run it to see the results. It seems pretty easy to use. OLTP stands for Online Transaction Processing, is a class of software applications capable of supporting transaction-oriented programs. An important attribute of an OLTP system is its ability to maintain concurrency. OLTP systems often follow a decentralized architecture to avoid single points of failure. These systems are generally designed for a large audience of end-users who conduct short transactions. Queries involved in such databases are generally simple, need fast response times, and return relatively few records. A number of transactions per second acts as an effective measure for such systems. This one might seem more complicated, but it’s still a basic SQL query. It is used when you want to show the total values for each group but you want to include only specific rows in the sum. Query

Exercise 8: Grouping Data by Multiple Columns

Understanding SQL theory – including database design principles and query syntax – is essential. However, knowledge alone won't make you proficient. Actual querying experience bridges the gap between theory and application, enabling you to translate your knowledge into practical solutions. 2. Building ‘Muscle Memory’ A database cursor is a control structure that allows for the traversal of records in a database. Cursors, in addition, facilitates processing after traversal, such as retrieval, addition, and deletion of database records. They can be viewed as a pointer to one row in a set of rows. Exercise: For each movie, select the movie title, the IMDb rating, and the year the movie was released.

INTO @name CLOSE db_cursor /* Close the cursor and deallocate the resources */ DEALLOCATE db_cursor 23. What are Entities and Relationships? The query is the same as the last one, only this time we use the AVG() function, as we want to calculate the average salary by department. LEFT (OUTER) JOIN: Retrieves all the records/rows from the left and the matched records/rows from the right table. Full-Text Search is the method of searching single or collection of documents stored on a computer in a full-text based database. This is mostly supported in advanced database systems like SOLR or ElasticSearch. However, the feature is present but is pretty basic in PostgreSQL. 24. What are parallel queries in PostgreSQL?

That Was Fun! Now, Time to Do SQL Practice on Your Own!

Select the department from the table employees. Then, use the COUNT() aggregate function. In this case, we use the COUNT(*) version, which counts all the rows. We give the column the alias employees_by_department. The query actually selects three, not two columns. It’s the same as with two columns: simply write them in SELECT and separate them with commas. The output shows all the departments and the sum of total monthly salary costs by department. 12. Using COUNT() and GROUP BY Once again, this basic SQL query example is useful when you want to select several columns but not all the rows from the table. Now you want to find the values that are the same as the value from the condition. For that, you need the equality condition ( =). Query