SQL SELECT

The SELECT statement in SQL is used to retrieve data from a relational database.

Syntax

"table_name" is the name of the table where data is stored, and "column_name" is the name of the column containing the data to be retrieved.

To select more than one column, add a comma to the name of the previous column, and then add the column name. If you are selecting three columns, the syntax will be,

SELECT "column_name1", "column_name2", "column_name3" FROM "table_name";

Note there is no comma after the last column selected.

Special Case

Note that the FROM keyword appears in all of the scenarios above, since the FROM keyword is used to indicate which table(s) one is retrieving the data from. There is one special case where FROM does not exist, and that is when you are doing a mathematical operation. In this case, the syntax is simply,

SELECT [Math Operation];

Examples

We will provide examples for each of the following four use cases:

• Retrieve one column
• Retrieve multiple columns
• Retrieve all columns
• Do math operation

Let's use the following table to illustrate all three cases:

Table Store_Information

Example 1: Select one column

To select a single column, we specify the column name between SELECT and FROM as follows:

SELECT Store_Name FROM Store_Information;

Result:

Example 2: Select multiple columns

We can use the SELECT statement to retrieve more than one column. To select Store_Name and Sales columns from Store_Information, we use the following SQL:

SELECT Store_Name, Sales FROM Store_Information;

Result:

Example 3: Select all columns

There are two ways to select all columns from a table. The first is to list the column name of each column. The second, and the easier, way is to use the symbol *. For example, to select all columns from Store_Information, we issue the following SQL:

SELECT * FROM Store_Information;

Result:

Example 4: Math operation

If we want to use the SELECT statement to calculate 2+3, we issue the following SQL:

SELECT 2+3;

Result:

Exercises

For these exercises, assume we have a table called Users with the following columns:

Table Users

1. Which of the following SQL statement is incorrect? (There can be more than one answer)
a) SELECT * FROM Users;
b) SELECT First_Name, Gender, Last_Name FROM Users;
c) SELECT First_Name, Last_Name Users;
d) SELECT All FROM Users;

2. (True Or False) In SQL, the order of the columns in a SELECT statement must be the same as the order of the columns in the underlying table. For example, in the table Users, you must select First_Name before Last_Name.

3. (True Or False) The following two SQL statements are equivalent:
a) Select * From Users;
b) SELECT * FROM Users;