Generally SQL statements are divided into two types.
DDL – Data Definition Language Statements
DDL statements are used to create, alter and drop schema objects.
Some of the examples of DDL statements are
shown below.
1.
SQL statement to create a table
Create table EMP
(empno Number,
Name Varchar2(10),
Address Varchar2(50),
Sal Number,
Dept Number);
This query creates EMP table with columns mentioned in the bracket.
2.
ALTER TABLE
This statement is used to add, delete or modify column in the table
ALTER TABLE EMP
ADD Bonus Number;
This query will add new column Bonus in EMP table.
ALTER TABLE EMP
DROP COLUMN Dept;
This query will delete the Dept column from the EMP table.
3.
DROP – This statement can be used to drop table,
functions, procedure and packages in the oracle.
Drop table EMP;
The above statement will drop the
EMP table from the database.
Like this you can use this DROP
statement with procedure, function and packages in Oracle.
DML – Data Manipulation Language Statements.
These statements are used to access and
modify data from the schema objects.
SELECT – This statement can be used to
retrieve data from database tables.
SELECT * FROM EMP;
This query will
retrieve all records from the EMP table.
INSERT
– This statement can be used to insert records into tables.
INSERT INTO EMP
(EMPNO, NAME, ADDRESS, SAL, DEPT)
VALUES(1, ‘andrew morrey’, ‘Newyork’, ‘10000’, 10);
This query will
insert one record in EMP table.
UPDATE
– This statement can be used to modify any column value in the existing
records.
UPDATE EMP SET SAL = 10000;
This query will update SAL column value to 10000 for all
records in the
EMP table.
DELETE
– It is used to delete any record from the table.
DELETE from EMP;
This statement can delete all records from the EMP table.
DELETE from EMP WHRE EMPNO = 1;
It will delete record only for the employee number 1.
Apart from these, there is also one more important type
of SQL statements is Transaction Control Statements.
Transaction Control Statements are used to manage the data
changes made by DML statements.
COMMIT, ROLLBACK, SAVEPOINT and SET TRANSACTION are the
transaction control statements. These statements can be used in PL/SQL to
control the transaction.
This is the brief introduction of the SQL statements. You
can learn SQL statements in detail in the next sections.
In the next section of PLSQL Learning Point, you can
learn SQL statements syntax, when to use them and more practical examples of SQL
statements.