SCHEMAs in TSQL SQL SERVER

SCHEMA:

It is nothing but a logical container Under a database or we can group a set of objects under database by using a SCHEMA.

We can able to Create objects(Tables,views,procedures,functions,triggers etc) under a SCHEMA.

Creating a SCHEMA:

We can Create a schema by using the below syntax

syntax:

CREATE SCHEMA <SCHEMA_name>

Example:

CREATE SCHEMA SALES
CREATE SCHEMA EMPLOYEE

Creating an Object Under SCHEMA:

If we cant to Create an object under SCHEMA,we need to prefex the SCHEMA name before the object name as follows.

CREATE table SALES.TEST
 (
id int,
 name varchar(20)
 )

So we created the table called TEST under the SALES SCHEMA.

SELECT  * FROM TEST
--If  we used the above statement we will get an error that the object is not available,As the SQL server will look for a table under default SCHEMA dbo.So we need to write a Query as below.

SELECT  * FROM SALES.TEST

Like this we can Create any object under this SCHEMA and we can use it with SCHEMA.object Name where ever it requires.

Altering a SCHEMA:
we can Move an object from one SCHEMA to another by following the below syntax.

Syntax:

 ALTER SCHEMA <target_SCHEMA_name>
 transfer <source_SCHEMA_name.objectName>

example:

 ALTER SCHEMA SALES transfer dbo.dept

In the above example we are transfering the table dept from dbo SCHEMA to SALES SCHEMA,so that complete object willmove to SALES SCHEMA.

SELECT  * FROM  DEPT
 --in valid

SELECT  * FROM  SALES.DEPT
 --valid

Example 2:
Creating a view called VIEW1 in dbo SCHEMA as follows

 CREATE view VIEW1
 as
 select top 2 * from books

 SELECT  * FROM VIEW1

Transfering the view from dbo SCHEMA to SALES SCHEMA as folows

ALTER SCHEMA SALES transfer dbo.VIEW1

 SELECT  * FROM VIEW1
--in valid(throws an error)

 SELECT  * FROM SALES.VIEW1

Example 3:
Transfering an object from SALES SCHEMA to dbo SCHEMA(default)

ALTER SCHEMA dbo transfer SALES.TEST

 SELECT  * FROM TEST

 Droping a SCHEMA:

We can Drop the SCHEMA by using the below syntax

syntax:

 DROP SCHEMA <SCHEMA_name>

Example:

 DROP SCHEMA SALES
 --Cannot Drop SCHEMA 'SALES' because it is being referenced by object 'dept'.

NOTE:
 If we want to Drop a scehma we need to Drop all the objects unedr that SCHEMA or transfer all the obects to other scehmas and make the SCHEMA as empty then only we  can Drop a Schema.

I have two objects under the SALES Schema so i am unable to Drop the Schema.

 DROP view SALES.VIEW1
ALTER SCHEMA dbo transfer SALES.dept

I dropped one object under that Schema and trnsfered one object to another Schema and made the Schema empty now we are good to drop a Schema.

DROP SCHEMA SALES

Let me know if you need any more information on this.

Thanks
SQL SRINIVAS