SQL Statements

SQL use the term query as the name for its commands. Basically, all SQL code is written in the form of a query statement and then executed against a database.

All SQL queries perform some type of data operation such as selecting data, inserting/updating data, or creating data objects such as SQL databases and SQL tables.
Each query statement begins with a clause such as SELECT,UPDATE, CREATE or DELETE and ends with semicolon(;)

Important point to be noted is that SQL is not case sensitive language which means SELECT and select have same meaning in SQL statements but MySQL make difference in table names. So if you are working with MySQL then you need to give table names as they exist in the database.

SQL Statements

We can classify the SQL statements as follows:

Data retrieval	SELECT
Data manipulation language (DML)	INSERT
	UPDATE
	DELETE
Data definition language (DDL)	CREATE
	ALTER
	DROP
	RENAME
	TRUNCATE
Transaction control	COMMIT
	ROLLBACK
	SAVEPOINT
Data control language (DCL)	GRANT
	REVOKE

Example table to explain these commands:

We will use the following table to explain the next few chapters, assume this table name as ‘Employee‘.

EID	Department	Name	Salary
1	Research	Ravi	22000
2	HR	Mike	33000
3	Admin	Neel	25000
4	Sales	Anna	30000
5	HR	Jo	20000
6	Admin	Sunil	25000
7	Sales	Mark	28000
8	Research	Bill	35000
9	HR	Tim	40000
10	Research	Sharan	32000

Select Statement:

SELECT QUERY allows you to retrieve records from one or more tables from database.

Syntax:

[code language=”sql”] SELECT columns FROM tables WHERE <condition>

We often us WHERE Clause with SELECT Statement:

[code language=”sql”] Where {expression | column} “operator” {expression | column}[and|or] {expression | column} “operator” {expression | column}

Examples on SELECT:

Example 1: Retrieving entire data from Employee table:

[code language=”sql”] SELECT * FROM Employee

Here * indicates all the columns of the table.

Output:

EID	Department	Name	Salary
1	Research	Ravi	22000
2	HR	Mike	33000
3	Admin	Neel	25000
4	Sales	Anna	30000
5	HR	Jo	20000
6	Admin	Sunil	25000
7	Sales	Mark	28000
8	Research	Bill	35000
9	HR	Tim	40000
10	Research	Sharan	32000

Example 2: Retrieving the data from Employee table where the department is Research:

[code language=”sql”] SELECT * FROM Employee WHERE Department="Research"

Here * indicates all the columns of the table.

Output:

EID	Department	Name	Salary
1	Research	Ravi	22000
8	Research	Bill	35000
10	Research	Sharan	32000

Example 1: Retrieving EID and Name from Employee table where salary is grater than 22000:

[code language=”sql”] SELECT EID, Name FROM Employee WHERE Salary>22000

Here * indicates all the columns of the table.

Output:

EID	Name
2	Mike
3	Neel
4	Anna
6	Sunil
7	Mark
8	Bill
9	Tim
10	Sharan

We will see more examples on SELECT statement later with more examples.