Querying data from multiple tables in SQL allows you to combine data from different tables into a single result set. There are several ways to query data from multiple tables, including using INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL OUTER JOIN.
To query data from two tables, you use the JOIN clause in your SELECT statement. The syntax is as follows:
SELECT column1, column2, ...
FROM table1
JOIN table2
ON table1.column = table2.column;Where table1 and table2 are the names of the tables you want to join, ON clause specifies the condition that links the two tables based on a common column between them. The SELECT statement then defines which columns you want to retrieve from the joined tables.
To query data from three tables, you simply add another JOIN clause to the SELECT statement:
SELECT column1, column2, ...
FROM table1
JOIN table2
ON table1.column = table2.column
JOIN table3
ON table2.column = table3.column;
In this example, table1 is joined with table2 based on a common column specified in the ON clause, and then table2 is joined with table3 based on another common column.
It’s important to note that the order of the JOIN clauses in the SELECT statement affects the result set. The first table is the driving table and the other tables are joined to it based on the ON clause conditions.
Querying data from multiple tables in SQL allows you to combine data from different tables into a single result set. By using the JOIN clause, you can retrieve the desired columns from two or more tables based on a common column.