How to find the first day of a month

By using the format string MM to extract the month, and then using the DAY format to return the first day of the month within the date , it is possible to find first day of a month:

select
   to_char(
      trunc(:p_date,'MM'),'DAY'
       )
from dual;

How to find dates between two given dates

By using below query, it is possible to generate dates between to given dates. 

SELECT start_date - 1 + rownum as p_date
FROM all_objects
WHERE start_date - 1 + rownum <= end_date

VIEW

This SQL tutorial explains how to create, update, and drop SQL VIEWS with syntax and examples.

DESCRIPTION

The SQL VIEW is, in essence, a virtual table that does not physically exist. Rather, it is created by a SQL statement that joins one or more tables.

CREATE SQL VIEW

Syntax

The syntax for the SQL CREATE VIEW Statement is:

CREATE VIEW view_name AS
  SELECT columns
  FROM tables
  [WHERE conditions];

view_name

The name of the SQL VIEW that you wish to create.

WHERE conditions

Optional. The conditions that must be met for the records to be included in the VIEW.

Example

Here is an example of how to use the SQL CREATE VIEW:

CREATE VIEW sup_orders AS
  SELECT suppliers.supplier_id, orders.quantity, orders.price
  FROM suppliers
  INNER JOIN orders
  ON suppliers.supplier_id = orders.supplier_id
  WHERE suppliers.supplier_name = 'IBM';

This SQL CREATE VIEW example would create a virtual table based on the result set of the select statement. You can now query the SQL VIEW as follows:

SELECT *
FROM sup_orders;

UPDATE SQL VIEW

You can modify the definition of a SQL VIEW without dropping it by using the SQL CREATE OR REPLACE VIEW Statement.

Syntax

The syntax for the SQL CREATE OR REPLACE VIEW Statement is:

CREATE OR REPLACE VIEW view_name AS
  SELECT columns
  FROM table
  [WHERE conditions];

Example

Here is an example of how you would use the SQL CREATE OR REPLACE VIEW Statement:

CREATE or REPLACE VIEW sup_orders AS
  SELECT suppliers.supplier_id, orders.quantity, orders.price
  FROM suppliers
  INNER JOIN orders
  ON suppliers.supplier_id = orders.supplier_id
  WHERE suppliers.supplier_name = 'Microsoft';

This SQL CREATE OR REPLACE VIEW example would update the definition of the SQL VIEW called sup_orders without dropping it. If the SQL VIEW did not yet exist, the SQL VIEW would merely be created for the first time.

DROP SQL VIEW

Once a SQL VIEW has been created, you can drop it with the SQL DROP VIEW Statement.

Syntax

The syntax for the SQL DROP VIEW Statement is:

DROP VIEW view_name;

view_name

The name of the view that you wish to drop.

Example

Here is an example of how to use the SQL DROP VIEW Statement:

DROP VIEW sup_orders;

This SQL DROP VIEW example would drop/delete the SQL VIEW called sup_orders.

LOCAL TEMPORARY TABLES

This SQL tutorial explains how to create SQL LOCAL TEMPORARY tables with syntax and examples.

DESCRIPTION

SQL LOCAL TEMPORARY TABLES are distinct within modules and embedded SQL programs within SQL sessions.

SYNTAX

The syntax for SQL DECLARE LOCAL TEMPORARY TABLE is:

DECLARE LOCAL TEMPORARY TABLE table_name
( column1 datatype [ NULL | NOT NULL ],
  column2 datatype [ NULL | NOT NULL ],
  ...
);

Parameters or Arguments

table_name

The name of the local temporary table that you wish to create.

column1, column2

The columns that you wish to create in the local temporary table. Each column must have a datatype. The column should either be defined as NULL or NOT NULL and if this value is left blank, the database assumes NULL as the default.

EXAMPLE

Let's look at a SQL DECLARE LOCAL TEMPORARY TABLE example:

DECLARE LOCAL TEMPORARY TABLE suppliers_temp
( supplier_id int NOT NULL,
  supplier_name char(50) NOT NULL,
  contact_name char(50)
);

This example would create a LOCAL TEMPORARY TABLE called suppliers_temp.

GLOBAL TEMPORARY TABLES

This SQL tutorial explains how to create SQL GLOBAL TEMORARY tables with syntax and examples.

DESCRIPTION

SQL GLOBAL TEMPORARY TABLES are tables that are created distinct within SQL sessions.

SYNTAX

The syntax for SQL CREATE GLOBAL TEMPORARY TABLE is:

CREATE GLOBAL TEMPORARY TABLE table_name
( column1 datatype [ NULL | NOT NULL ],
  column2 datatype [ NULL | NOT NULL ],
  ...
);

Parameters or Arguments

table_name

The name of the global temporary table that you wish to create.

column1, column2

The columns that you wish to create in the global temporary table. Each column must have a datatype. The column should either be defined as NULL or NOT NULL and if this value is left blank, the database assumes NULL as the default.

EXAMPLE

Let's look at a SQL CREATE GLOBAL TEMPORARY TABLE example:

CREATE GLOBAL TEMPORARY TABLE suppliers_temp
( supplier_id numeric(10) NOT NULL,
  supplier_name char(50) NOT NULL,
  contact_name char(50)
);

DROP TABLE STATEMENT

This SQL tutorial explains how to use the SQL DROP TABLE statement with syntax and examples.

DESCRIPTION

The SQL DROP TABLE statement allows you to remove or delete a table from the SQL database.

SYNTAX

The syntax for the SQL DROP TABLE statement is:

DROP TABLE table_name;

Parameters or Arguments

table_name

The name of the table to remove from the database.

EXAMPLE

You may have found that you've created a table that you no longer require. You can use the DROP TABLE statement to remove the table from your database.

Let's look at an example that shows how to drop a table using the DROP TABLE statement.

For example:

DROP TABLE suppliers;

This DROP TABLE statement example would drop the table called suppliers. This would both remove the records associated with the suppliers table as well as its table definition.

Once you have dropped the table, you can recreate the suppliers table without getting an error that the table already exists.

Let's look at one more example where we prefix the table name with the database name.

For example:

DROP TABLE totn.contacts;

In this example, e have dropped a table called contacts that is in the totn database.

ALTER TABLE STATEMENT

This SQL tutorial explains how to use the SQL ALTER TABLE statement to add a column, modify a column, drop a column, rename a column or rename a table (with lots of clear, concise examples). We've also added some practice exercises that you can try for yourself.

DESCRIPTION

The SQL ALTER TABLE statement is used to add, modify, or drop/delete columns in a table. The SQL ALTER TABLE statement is also used to rename a table.

ADD COLUMN IN TABLE

Syntax

To add a column in a table, the SQL ALTER TABLE syntax is:

ALTER TABLE table_name
  ADD column_name column-definition;

Example

Let's look at a SQL ALTER TABLE example that adds a column.

For example:

ALTER TABLE supplier
  ADD supplier_name char(50);

This SQL ALTER TABLE example will add a column called supplier_name to the supplier table.

ADD MULTIPLE COLUMNS IN TABLE

Syntax

To add multiple columns to an existing table, the SQL ALTER TABLE syntax is:

ALTER TABLE table_name
  ADD (column_1 column-definition,
       column_2 column-definition,
       ...
       column_n column_definition);

Example

Let's look at SQL ALTER TABLE example that adds more than one column.

For example:

ALTER TABLE supplier
  ADD (supplier_name char(50),
       city char(45));

This SQL ALTER TABLE example will add two columns, supplier_name as a char(50) field and city as a char(45) field to thesupplier table.

MODIFY COLUMN IN TABLE

Syntax

To modify a column in an existing table, the SQL ALTER TABLE syntax is:

For Oracle, MySQL, MariaDB:

ALTER TABLE table_name
  MODIFY column_name column_type;

For SQL Server:

ALTER TABLE table_name
  ALTER COLUMN column_name column_type;

For PostgreSQL:

ALTER TABLE table_name
  ALTER COLUMN column_name TYPE column_definition;

Example

Let's look at an example of how to modify a column called supplier_name using the ALTER TABLE statement. Note that most databases have a slightly different syntax.

For Oracle:

ALTER TABLE supplier
  MODIFY supplier_name char(100) NOT NULL;

For MySQL and MariaDB:

ALTER TABLE supplier
  MODIFY supplier_name VARCHAR(100) NOT NULL;

For SQL Server:

ALTER TABLE supplier
  ALTER COLUMN supplier_name VARCHAR(100) NOT NULL;

For PostgreSQL:

ALTER TABLE supplier
  ALTER COLUMN supplier_name TYPE CHAR(100),
  ALTER COLUMN supplier_name SET NOT NULL;

MODIFY MULTIPLE COLUMNS IN TABLE

Syntax

To modify multiple columns in an existing table, the SQL ALTER TABLE syntax is:

For Oracle:

ALTER TABLE table_name
  MODIFY (column_1 column_type,
          column_2 column_type,
          ...
          column_n column_type);

For MySQL and MariaDB:

ALTER TABLE table_name
  MODIFY column_1 column_definition
    [ FIRST | AFTER column_name ],
  MODIFY column_2 column_definition
    [ FIRST | AFTER column_name ],
  ...
;

For PostgreSQL:

ALTER TABLE table_name
  ALTER COLUMN column_name TYPE column_definition,
  ALTER COLUMN column_name TYPE column_definition,
  ...
;

Example

Let's look at an example that uses the ALTER TABLE statement to modify more than one column. In this example, we will modify two columns called supplier_name and city.

For Oracle:

ALTER TABLE supplier
  MODIFY (supplier_name char(100) NOT NULL,
          city char(75));

For MySQL and MariaDB:

ALTER TABLE supplier
  MODIFY supplier_name VARCHAR(100) NOT NULL,
  MODIFY city VARCHAR(75);

For PostgreSQL:

ALTER TABLE supplier
  ALTER COLUMN supplier_name TYPE CHAR(100),
  ALTER COLUMN supplier_name SET NOT NULL,
  ALTER COLUMN city TYPE CHAR(75);

DROP COLUMN IN TABLE

Syntax

To drop a column in an existing table, the SQL ALTER TABLE syntax is:

ALTER TABLE table_name
  DROP COLUMN column_name;

Example

Let's look at an example that drops (ie: deletes) a column from a table.

For example:

ALTER TABLE supplier
  DROP COLUMN supplier_name;

This SQL ALTER TABLE example will drop the column called supplier_name from the table called supplier.

RENAME COLUMN IN TABLE

Syntax

To rename a column in an existing table, the SQL ALTER TABLE syntax is:

For Oracle and PostgreSQL:

ALTER TABLE table_name
  RENAME COLUMN old_name TO new_name;

For SQL Server (using the stored procedure called sp_rename):

sp_rename 'table_name.old_column', 'new_name', 'COLUMN';

For MySQL and MariaDB:

ALTER TABLE table_name
  CHANGE COLUMN old_name TO new_name;

Example

Let's look at an example that renames a column in the supplier table from supplier_name to sname.

For Oracle (9i Rel2 and up) and PostgreSQL:

ALTER TABLE supplier
  RENAME COLUMN supplier_name TO sname;

For SQL Server (using the stored procedure called sp_rename):

sp_rename 'supplier.supplier_name', 'sname', 'COLUMN';

For MySQL and MariaDB:

ALTER TABLE supplier
  CHANGE COLUMN supplier_name sname VARCHAR(100);

In MySQL and MariaDB, you must specify the data type of the column when you rename it.

RENAME TABLE

Syntax

To rename a table, the SQL ALTER TABLE syntax is:

For Oracle, MySQL, MariaDB, PostgreSQL and SQLite:

ALTER TABLE table_name
  RENAME TO new_table_name;

For SQL Server (using the stored procedure called sp_rename):

sp_rename 'table_name', 'new_table_name';

Example

Let's look at an example that renames a table called supplier to the new name vendor.

For Oracle, MySQL, MariaDB, PostgreSQL and SQLite:

ALTER TABLE supplier
  RENAME TO vendor;

For SQL Server (using the stored procedure called sp_rename):

sp_rename 'supplier', 'vendor';