The SELECT statement is used to retrieve data from one or more tables in a relational database. The basic syntax of the SELECT statement is as follows:
SELECT column1, column2, ..., column_n
FROM table_name;
In this syntax, the column1, column2, …, column_n represent the columns that you want to retrieve data from, and table_name represents the name of the table from which you want to retrieve data. The SELECT statement can retrieve data from one or more tables using a join operation, which combines data from multiple tables based on a common column.
Let’s take a look at a few examples to understand the SELECT statement better:
Example 1:
SELECT name, age, city
FROM students;
In this example, the SELECT statement retrieves the name, age, and city columns from the students table. The result of this query will be a table that displays the name, age, and city of all the students in the students table.
Example 2:
SELECT name, marks, subject
FROM marks
WHERE marks >= 80;
In this example, the SELECT statement retrieves the name, marks, and subject columns from the marks table where the marks are greater than or equal to 80. The result of this query will be a table that displays the name, marks, and subject of all the students who scored 80 or more marks in the marks table.
Example 3:
SELECT students.name, marks.subject, marks.marks
FROM students
JOIN marks
ON students.student_id = marks.student_id;
In this example, the SELECT statement joins the data from the students and marks tables based on the common student_id column. The result of this query will be a table that displays the name of the student, the subject, and the marks for all the students in the students and marks tables.
In conclusion, the SELECT statement is an essential tool for retrieving data from a relational database. It provides a flexible and powerful way to retrieve data from one or more tables based on various conditions and join operations.
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