What is the command for SQL
Structured Query Language is instruction, it is used to communicate to database how to use and how will be monitored & manage them to SQL following are comm-and for SQL (Structured query language).
Some Of The Most Important SQL Commands
CREATE DATABASE – creates a new database.
Create
database databasename;
CREATE TABLE – create a new table
CREATE
TABLE table_name
(
column_name1 data_type(size),
column_name2 data_type(size)’
column_name3 data type(size),
…
);
The column_name parameters specify
the names of the columns of the table.
The data type parameter specifies what
type of data the column can hold (e.g. varchar, integer, decimal, date,
etc.).
The size parameter specifies the maximum length of the column of the
table.
Example:
CREATE TABLE suppliers
(supplier_id number(10)
NOT NULL,
Supplier_name varchar 2(50) NOT NULL,
contact_name varchar2(50);
The ALTER TABLE Statement
The ALTER TABLE statement
is used to add, delete, or modify columns in an existing table.
SQL ALTER TABLE Syntax
To add the column: To add
a column in a table, use the following syntax:
ALTER TABLE table_name
DROP COLUMN column_name
Example:
ADD (supplier_name
vaechar2(50),
City varchar2(45);
To delete the column:
To delete a column in a table, use the following syntax (notice that
some database systems don’t allow deleting a column):
ALTER TABLE table_name
DROP COLUMN column_name
Example:
ALTER TABLE supplier
DROP COLUMN supplier_name;
To modify the column: To change the data type of a column in table,
use the following syntax:
SQL
Server / MS Access :
ALTER TABLE
table_name
ALTER COLUMN
column_name datatype
My SQL/ Oracle (prior version 10G)
ALTER TABLE
table_name
MODIFY COLUMN
column_name datatype
Example:
ALTER TABLE supplier
MODIFY
supplier_name varchar2(100) not null;
Oracle 10G and later:
ALTER TABLE table_name
MODIFY column_name
datatype
Rename column in table
Syntax
To rename a column in an
existing table; the SQL ALTER TABES syntax is:
ALTER TABLE
table_name
RENAME COLUMN old_name to new_name;
For example:
ALTER TABLE supplier
RENAME COLUMN supplier_name to sname;
The DROP TABLE Statement
The DROP TABLE
statement is use to delete a table.
Drop table
tablename;
The DROP DATABASE Statement
The DROP DATABASE
statement is used to delete a database.
DROP DATABASE
database_name
The TRUNCATE TABLE Statement
What if we only
want to delete the data inside the table, and not the table itself?
Then, use the
TRUNCATE TABLE statement:
TRUNCATE TABLE
table_name
The SQL INSERT INTO Statement
The INSERT INTO statement is
used to insert new records in a table.
SQL INSERT INTO Syntax
It is possible to
write the INSERT INTO statement in two forms.
The first form
does not specify the column names where the date will data will be inserted,
only their values:
INSERT INTO table_name
VALUES
(value1,value2,value3,...);
Example:
INSERT INTO sup;iers
(supplier_id,
supplier_name)
VALUES
(24553,’IBM’);
The SQL SELECT Statement
The SELECT
statement is used to select data from a database.
The result is
stored in a result table, called the
result-set.
SQL SELECT Syntax
SELECT column _name, column_name
FROM table_name
And
SELECT* FROM table_name;
Example:
SELECT
supplier_name,city,state
FROM
supplier
The
SQL WHARE Clause
The WHERE clause is used to extract only those
records the fulfill a specified
criterion.
SQL WHERE Syntax
SELECT column_name,column_name
FROM table_name
WHERE column_name operator value;
Operators in The WHERE Clause
The WHERE
clause is used in the WHERE clause:
Operator
|
Description
|
=
|
Equal
|
<>
|
Not equal. Note: In
some version of SQL this operator may be written as ! =
|
>
|
Greater than
|
<
|
Less than
|
>=
|
Greater than or equal
|
<=
|
Less than or equal
|
BETWEEM
|
Between an inclusive
range
|
LIKE
|
Search for a pattern
|
IN
|
To specify multiple
possible values for a column
|
The SQL AND & OR Operators
The AND operator
displays a record if both first condition AND the second condition are true.
The OR operator displays
a records if either the first condition OR the second condition is true.
SELECT ID, NAME, SALARY
FROM CUSTOMERS
WHERE SALARY > 2000
AND age < 25;
Following is an example,
which would fetch ID, Name and Salary
fields from the CUSTOMERS table where salary is greater than 2000 AND age is
less than 25 years.
SELECT ID, NAME, SALARY
FROM CUSTOMERS
WHERE SALARY > 2000
OR age < 25;
Following is an example,
which would fetch ID, Name and Salary field the CUSTOMERS table where salary is
greater than 2000 OR age is less than 25 years.
SQL LIKE Operator:
The LIKE operator is used in a WHERE clause to search for a
specified pattern in a column.
SELECT COLUMN_name(s)
FROM table_name
WHERE column_name LIKE pattern
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