Concept explainers
“SELECT” command:
The “SELECT” command is used to retrieve data in a
Syntax for selecting values from the table is as follows:
SELECT STUDENT_ID FROM STUDENT;
- The given query is used to display each student ID from “STUDENT” table.
“COUNT” function:
- It is the one function of aggregate function.
- The “COUNT” function is used to compute the number of rows in a table.
Example:
The example for “COUNT” function is given below:
SELECT COUNT(*) FROM STUDENT WHERE MARK_CREDIT >= 90;
The above query is used to display the number of students whose mark credit is greater or equal to “90” by using “COUNT” function.
- From the given query, the asterisk (*) represent any column.
- User can also count the number of rows in a query by selecting a particular column instead of using the asterisk.
- The below example is as follows
SELECT COUNT(STUDENT_ID) FROM STUDENT WHERE MARK_CREDIT >= 90;
- The below example is as follows
“ORDER BY” Clause:
- User can sort the data in specific order using “ORDER BY” clause.
- The column on which to sort data is called a sort key or a simple key.
- To sort the output, use an “ORDER BY” clause followed by the sort key.
- If the user does not indicate a sort order, the output displayed in default order that is ascending order.
Example:
The example for “ORDER BY” clause is given below:
SELECT STUDENT_ID, STUDENT_NAME, STUDENT_CREDIT FROM STUDENT ORDER BY STUDENT_CREDIT;
The above query is used to list student ID, name and credit for each student with ascending order of student credit using an “ORDER BY” clause.
- From the given query, the sort key is “STUDENT_CREDIT”. So, the rows are sorted in ascending order by “STUDENT_CREDIT”.
“GROUP BY” Clause:
- User can group the data using “GROUP BY” clause.
- This clause allows the user to group data on a specific column and then computes statistics when user preferred.
Example:
The example for “GROUP BY” clause is given below:
SELECT CUSTOMER_NAME, SUM(AMOUNT) FROM CUSTOMERS GROUP BY CUSTOMER_NAME;
The above query is used to list the customer name and the sum of amount using “GROUP BY” clause.

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Chapter 4 Solutions
A GUIDE TO SQL
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