SQL (Structured Query Language) is a programming language used to manage and manipulate relational databases. With SQL, developers can perform various operations on a database, such as creating tables, inserting and updating data, and retrieving specific information.
In this article, we will explore the main features in SQL that every developer should know. From basic functions like SELECT and UPDATE to more advanced functions like JOIN and GROUP BY, we'll delve into how they work and how to use them effectively in your database queries.
SELECT: Retrieve data from a table
The SELECT function is one of the most used functions in SQL. Allows you to retrieve data stored in a specific table. You can select all columns in the table using the asterisk (*) or select specific columns according to your needs.
SELECT * FROM table; SELECT column1, column2 FROM table;
In the first example, we retrieve all columns from the table "table". In the second example, we select only the columns "column1" and "column2".
INSERT: Insert new data into a table
The INSERT function is used to add new records into a table. You can specify the values you want to insert into each column or you can insert values from another table.
INSERT INTO table (column1, column2) VALUES (value1, value2); INSERT INTO table SELECT column1, column2 FROM other_table;
In the first example, we insert the values "value1" and "value2" into the columns "column1" and "column2" respectively. In the second example, we insert the values of the columns "column1" and "column2" of the table "other_table" into the table "table".
UPDATE: Update existing data in a table
The UPDATE function is used to modify existing data in a table. You can update all records in a table or you can select specific records to update.
UPDATE table SET column1 = value1 WHERE condition;
In this example, we update the value of "column1" to "value1" for records that meet the specified condition.
DELETE: Delete records from a table
The DELETE function is used to delete records from a table. You can delete all records from a table or you can select specific records to delete.
DELETE FROM table WHERE condition;
In this example, we delete records that meet the specified condition.
JOIN: Combine data from multiple tables
The JOIN function is used to combine data from two or more tables based on a common column. There are different types of JOIN, such as INNER JOIN, LEFT JOIN, and RIGHT JOIN, which determine how data in tables is combined.
SELECT column1, column2 FROM table1 JOIN table2 ON table1.column = table2.column;
In this example, we combine the data from "table1" and "table2" based on the column "column". We select the columns "column1" and "column2" from the resulting table.
GROUP BY: Group data by a column
The GROUP BY function is used to group data based on the values in a column. It is useful when we want to perform aggregate operations, such as calculating the average or total, on groups of data.
SELECT column, AVG(column2) FROM table GROUP BY column;
In this example, we group the data based on the column "column" and calculate the average of "column2" for each group.
Conclusions
In summary, the main functions in SQL are SELECT, INSERT, UPDATE, DELETE, JOIN and GROUP BY. These functions allow you to efficiently manage and manipulate data in a relational database. It's important to understand how these functions work and how to use them in your queries to take full advantage of the potential of SQL.
Frequently asked questions
1. What are the main functions in SQL?
The main functions in SQL are SELECT, INSERT, UPDATE, DELETE, JOIN and GROUP BY. Each has its own functionality and is used to perform specific operations on a database.
2. What function is used to retrieve data from a table in SQL?
The function used to retrieve data from a table in SQL is SELECT. You can select all columns in the table or select specific columns according to your needs.
3. How do you combine data from multiple tables in SQL?
Data from multiple tables is combined using the JOIN function in SQL. You can combine data based on a common column to obtain integrated results.
4. What is the GROUP BY function used for in SQL?
The GROUP BY function is used to group data based on the values of a column in SQL. It is useful for performing aggregate operations, such as calculating the average or total, on groups of data.
5. How do you delete a record from a table in SQL?
To delete a record from a table in SQL, the DELETE function is used. You can delete all records from a table or select specific records to delete based on your needs.
6. What is the function used to add new records in a table in SQL?
The function used to add new records in a table in SQL is INSERT. You can specify the values you want to insert into each column or insert values from another table.
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