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Structured Query Language (SQL) is a powerful language used to manipulate and manage data in relational databases. As a fundamental tool for data analysis, SQL allows users to create, retrieve, update and delete database records. This blog post will guide you through the essentials of SQL and help you unlock the power of your data.
SQL Basics: Retrieving Data
The SQL SELECT statement extracts data from a database. The syntax for a basic SELECT statement is:
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SELECT column_name FROM table_name; |
This query pulls data from the specified column(s) for all rows in the specified table.
If you want to select all columns, you can use the wildcard character ‘*’:
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SELECT * FROM table_name; |
Filtering Data
To filter data in SQL, we use the WHERE clause. Here is the syntax:
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SELECT column_name FROM table_name WHERE condition; |
The condition is the criteria that rows must meet to be included in the result set. For example, the following statement returns records from the table ’employees’ where ’employee_age’ is greater than 35:
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SELECT * FROM employees WHERE employee_age > 35; |
Sorting Results
To sort the results in a specific order, use the ORDER BY clause. Here’s an example:
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SELECT column_name FROM table_name ORDER BY column_name ASC|DESC; |
ASC sorts the result set in ascending order and DESC in descending order.
Updating Records
SQL UPDATE statement allows us to modify existing records. Here’s how:
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UPDATE table_name SET column1 = value1, column2 = value2,... WHERE condition; |
For instance, to change the ‘salary’ column in the ’employees’ table:
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UPDATE employees SET salary = 50000 WHERE employee_id = 1; |
Deleting Records
The DELETE FROM statement in SQL is used to delete records from a database table. Here’s how to use it:
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DELETE FROM table_name WHERE condition; |
For example:
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DELETE FROM employees WHERE employee_id = 1; |
Be cautious when using the DELETE FROM statement without a WHERE condition, as it will delete all records from the table.
Conclusion
In conclusion, mastering the manipulation of databases with SQL is essential for anyone dealing with data. With CRUD (Create, Read, Update, Delete) operations, SQL provides powerful tools for managing your data. As always, remember to be cautious when updating or deleting records in your database, as these actions can’t be undone.