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SQL Commands
Understanding SQL command is essential for working with databases. SQL command allows user to retrieve, manipulate, and manage data stored in the databases. It include commands like SELECT, INSERT, UPDATE, DELETE, CREATE and DROP etc.
SQL statement :
SQL command is also referred to as "SQL statement".
SQL query :
A set of SQL command/statement used to retrieve data from a database is known as a "SQL query".
SQL commands can be broadly categorized into three types :
1. Data Definition Language (DDL)
2. Data Manipulation Language (DML)
3. Data Query Language (DQL)
These are some essential commands which form the core of SQL programming :
1. CREATE :
"CREATE" command is used to create a new database object such as a tables, functions, views and stored procedure. Here's is an example of creating [SQL Tutorial] table -
CREATE TABLE [SQL Tutorial] (
Sno INT PRIMARY KEY,
FirstName VARCHAR(50) NOT NULL,
LastName VARCHAR(50),
Age INT CHECK (age > 18),
Gender VARCHAR(10) CHECK (gender IN ('Male', 'Female')),
Salary DECIMAL(18,2)
);
2. DROP :
"DROP" command is used to delete a database object. Here's is an example of removing [SQL Tutorial] table -
DROP TABLE [SQL Tutorial];
3. ALTER :
"ALTER" command is used to modify the structure of an existing database object. Here's is an example of modifying the structure of the existing [SQL Tutorial] table -
ALTER TABLE [SQL Tutorial]
ADD Address VARCHAR(100);
4. TRUNCATE :
"TRUNCATE" command is used to remove all data from a table, while keeping the table structure intact. Here's is an example of removing all data from [SQL Tutorial] table -
TRUNCATE TABLE [SQL Tutorial];
5. INSERT :
"INSERT" command is used to add new data to a table. Here's is an example of adding new records in [SQL Tutorial] table -
INSERT INTO [SQL Tutorial] ( FirstName, Age )
VALUES ('Mike', 25),
('Tim', 35),
('Jim', 40);
6. UPDATE :
"UPDATE" command is used to modify existing data in a table. Here's is an example modifying existing data in [SQL Tutorial] table -
UPDATE [SQL Tutorial]
SET Gender = 'Male';
7. DELETE :
"DELETE" command is used to remove data from a table. Here's is an example removing data from [SQL Tutorial] table -
DELETE FROM [SQL Tutorial]
WHERE Age = 25;
8. SELECT :
"SELECT" command is used to retrieve data from one or more tables in a database. This command is the most commonly used command and is considered as the backbone of SQL. It is essential to understand this command in order to effectively work with relational databases. Here's is an example retrieving data from [SQL Tutorial] table -
SELECT * FROM [SQL Tutorial];