Most Used SQL Clauses in DBMS

SQL is a Structured Query Language which is the standard and most widely used programming language for relational databases. It is used to manage and organize data in all sorts of systems where all varieties of data relationships exist.

Structured Query Language (SQL) Clauses

The SQL clauses are of three types as shown below−

Let us learn about them one by one.

GROUP BY CLAUSE

SQL GROUP BY is used to arrange identical data into groups. It is used with the SQL SELECT statement. The GROUP BY statement follows the WHERE clause in a SELECT statement and precedes the ORDER BY clause. It is also used with aggregation functions.

The syntax is as follows −

SELECT column
FROM table_name
WHERE conditions
GROUP BY column
ORDER BY column

Example

Given below is an example for the use of Group By clause −

Create table product(pid number(10),company varchar2(20),qty number(10),rate number(10),cost number(10));
insert into product values(1,'LANCO', 20,450,4000);
insert into product values(2,'METRO',30,400,3000);
insert into product values(3,'Tata',40,350,4500);
select * from product;

Output

You will get the following output −

1|LANCO|20|450|4000
2|METRO|30|400|3000
3|Tata|40|350|4500

You can use the following command −

select company, count(*) from product group by company;

Output

You will get the following output −

LANCO|1
METRO|1
Tata|1

HAVING CLAUSE

It is used to search conditions for a group or an aggregate. It is generally used in Group by clause. If we are not using group by clause then we can use having clause just like where clause.

The syntax is as follows −

SELECT column1, column2
FROM table_name
WHERE conditions
GROUP BY column1, column2
HAVING conditions
ORDER BY column1, column2;

Example

Given below is an example for the use of Having clause −

Create table product(pid number(10),company varchar2(20),qty number(10),rate number(10),cost number(10));
insert into product values(1,'LANCO', 20,450,4000);
insert into product values(2,'METRO',30,400,3000);
insert into product values(3,'Tata',40,350,4500);
insert into product values(4,'Tata',30,250,5000);
insert into product values(5,'METRO',22,400,4500);
select * from product;

SELECT company, COUNT(*) FROM product group by company
having count(*)>1;

Output

You will get the following output −

1|LANCO|20|450|4000
2|METRO|30|400|3000
3|Tata|40|350|4500
4|Tata|30|250|5000
5|METRO|22|400|4500
METRO|2
Tata|2

ORDER BY Clause

This clause sorts the result in either ascending or descending order. By default, it does an ascending order if you don’t mention anything. ASC and DESC are the keywords used to order the records.

The syntax is as follows −

SELECT column1, column2
FROM table_name
WHERE condition
ORDER BY column1, column2... ASC|DESC;

Sorting in ascending order

Use the below mentioned command to sort in ascending order −

SELECT *
FROM product
ORDER BY company;

Output

You will get the following output −

1|LANCO|20|450|4000
2|METRO|30|400|3000
5|METRO|22|400|4500
3|Tata|40|350|4500
4|Tata|30|250|5000

Sorting in descending order

Use the below mentioned command to sort in descending order −

SELECT *
FROM product
ORDER BY company DESC;

Output

You will get the following output −

3|Tata|40|350|4500
4|Tata|30|250|5000
2|METRO|30|400|3000
5|METRO|22|400|4500
1|LANCO|20|450|4000