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Overview

The SELECT statement helps you obtain the data you need from one or more tables.

The application of this statement will be helpful in several cases listed below:

  • Evaluating data from only particular fields in a table.

  • Reviewing data from several tables at the same time.

  • Retrieving the data based on specific criteria.

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Syntax

To request data from a table using the SELECT statement, you can use the following syntax:

SELECT * FROM table_name;

You are allowed to filter the table by column. Refer to the syntax below.

SELECT column1, column2, ...
FROM table_name;

We will define each syntax as follows.

  • SELECT determines the data we need from the database or a table.

  • * referred to as select star or asterisk or represents all. It defines that the query should return all columns of the queried tables.

  • FROM clause indicates the table(s) to retrieve data from.

  • table_name represents the table(s) name.

  • column1, column2, ... these are used to specify the columns from where we want to retrieve the data.

The SELECT statement is case insensitive, which means select or SELECT has the same result.

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Examples

We have a table named student_data that stores the id, name, and where the student lives.

CREATE TABLE student_data (
  id int,
  name string,
  domicile string
);
INSERT INTO student_data 
    (id, name, domicile) 
VALUES 
    (119291,'Jordan','Los Angeles'),
    (119292,'Mike','Melbourne'),
    (119293,'Will','Sydney');
All the examples below are executed in the public schema. You can also display table from another specific schema. Click here for more info.

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#Case 1: Query data from all columns

  1. In the first case, we want to display all the data from the student_data table. Please refer to the syntax below:
SELECT * FROM table_name;
  1. Use the SELECT statement within the table name to get all the data:
SELECT * FROM student_data;
  1. If you have successfully run the query, you will get all the data from the student_data table.
+--------+----------+----------------+
| id     | name     | domicile       |
+--------+----------+----------------+
| 119291 | Jordan   | Los Angeles    | 
| 119292 | Mike     | Melbourne      |
| 119293 | Will     | Sydney         |
+--------+----------+----------------+

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#Case 2: Query data from specific columns

  1. We want to get the list of students’ names with their IDs. Please refer to the syntax below:
SELECT column_1, column_2 FROM table_name;
  1. Run the following query:
SELECT id, name FROM student_data;
  1. If you have successfully run the query, you will get a list of students’ IDs & names from the student_data table.
+--------+----------+
| id     | name     | 
+--------+----------+
| 119291 | Jordan   | 
| 119292 | Mike     |
| 119293 | Will     | 
+--------+----------+

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#Case 3: Query data from a specific column with the condition

  1. If we have a large number of data, skimming for the desired data will require a long time. We can apply some conditions to the SELECT statement. Please refer to the syntax below:
SELECT column_1 FROM table_name WHERE condition;
  1. Let’s say we want to know the student’s name who lives in Sydney, have a look and run the query below:
SELECT name FROM student_data WHERE domicile='Sydney';
  1. If you have successfully run the query, we now know that Will lives in Sydney.
+----------+ 
| name     | 
+----------+
| Will     | 
+----------+
CREATE INDEXINSERT INTO