My Sql concepts

Some points to consider when choosing Temporary, Global Temp Tables, between them:

Temporary Tables are real tables so you can do things like CREATE INDEXes, etc. If
you have large amounts of data for which accessing by index will be faster then
temporary tables are a good option.
Table variables can have indexes by using PRIMARY KEY or UNIQUE constraints. (If
you want a non-unique index just include the primary key column as the last column in
the unique constraint. If you don't have a unique column, you can use an identity
column.)
Table variables don't participate in transactions, logging or locking. This means they're
faster as they don't require the overhead, but conversely you don't get those features. So
for instance if you want to ROLLBACK midway through a procedure then table variables
populated during that transaction will still be populated!
Temp tables might result in stored procedures being recompiled, perhaps often. Table
variables will not.
You can create a temp table using SELECT INTO, which can be quicker to write (good
for ad-hoc querying) and may allow you to deal with changing datatypes over time, since
you don't need to define your temp table structure upfront.
You can pass table variables back from functions, enabling you to encapsulate and reuse
logic much easier (eg make a function to split a string into a table of values on some
arbitrary delimiter).
Using Table Variables within user-defined functions enables those functions to be used
more widely (see CREATE FUNCTION documentation for details). If you're writing a
function you should use table variables over temp tables unless there's a compelling need
otherwise.
Both table variables and temp tables are stored in tempdb. This means you should be
aware of issues such as COLLATION problems if your database collation is different to
your server collation; temp tables and table variables will by default inherit the collation
of the server, causing problems if you want to compare data in them with data in your
database.
Global Temp Tables (##tmp) are another type of temp table available to all sessions and
users.

Retrieving SQL Server Identity Column Values

Function

SCOPE_IDENTITY:: Returns the last identity value within the current execution scope.
SCOPE_IDENTITY is recommended for most scenarios.

@@IDENTITY:: Contains the last identity value generated in any table in the current session.
@@IDENTITY can be affected by triggers and may not return the identity value that you expect.

IDENT_CURRENT:: Returns the last identity value generated for a specific table in any session
and any scope.

Default Schema is “dbo.” Or define it
nVarchar takes double the size defined. It supports Unicode

create database Pragya

sp_who2
sp_helptext 'sp_who2'

use mydb
select * from demo1

--------------------------
use Pragya
create Table test1 (i int) --permanent
create Table #test1 (i int) --temp
create Table ##test1 (i int) --global temp
Declare test1(i int)

Create Table test2(i int)

Create Table Customer
(CustomerID INT IDENTITY (1000,1) Not Null
, Name nvarchar(100)
,CreateDateTime datetime
,CreditLimit decimal(12,5)
)
insert into Customer( Name,CreateDateTime, CreditLimit
) values ('test', Getdate(), 1000)

select * from Customer

Alter table customer
Add test nvarchar(200)

Alter table Customer
drop column test

Alter table Customer --not preferred
Add Primary Key (CustomerID)

Create Table CustPhone
(PhoneID int Primary Key, CustomerID int Null, Phone Int)

Alter table CustPhone
drop constraint FKCustomerID

Alter table CustPhone
Add Constraint UniqueName

Create Table Orders
(OrderID INT IDENTITY (1,1) Not Null Check (OrderID between 1 and 1000000)
, OrderDate datetime not null, CustomerID integer Foreign Key references
Customer(CustomerID))

insert into Orders(OrderDate) values ( Getdate())

Sp_help Orders

Four -Part Naming:: Server, Database, Schema, Object Name
A Cartesian join will get you a Cartesian product.
A Cartesian join is when you join every row of one table to every row of another table.
You can also get one by joining every row of a table to every row of itself.

SELECT [CustomerID]
,[AddressID]
,[AddressType]
,[rowguid]
,[ModifiedDate]
FROM [AdventureWorks].[SalesLT].[CustomerAddress]
where CustomerID= '29489'
and AddressID=' 1069'

GO

SELECT [CustomerID]
,[AddressID]
,[AddressType]
,[rowguid]
,[ModifiedDate]
or AddressID=' 1069'

SELECT [CustomerID]
,[AddressID]
,[AddressType]
,[rowguid]
,[ModifiedDate]
or AddressID=' 1069'
and AddressType= 'Main Office'

Click Display Estimated Executed Plan button on top
Retrieve Identity
select IDENT_CURRENT('Pragya')
select SCOPE_IDENTITY()
select @@IDENTITY

insert into Customer(Name, CreateDateTime, CreditLimit) values ('Hello',
GETDATE(), 5000)

sp_help Customer

select * from Customer

--not preferred
-- NON Clustered Primary Key
Alter table Orders
Add constraint PKCustomer1 Primary Key NONCLUSTERED (OrderID)
 Concatenate name
SELECT
[Title]
,[FirstName]
,[MiddleName]
,[LastName],' '+ isNull (Title, '')+ FirstName +LastName As EmpName

FROM [AdventureWorks].[SalesLT].[Customer]

--Self Join
SELECT emp.empid, emp.title, m.title, from emp E
inner join emp M on e.m_id=m.e_id

---Without join
SELECT emp.empid, emp.title, m.title, from emp E,
emp M where e.m_id=m.e_id

Select mgrId, COUNT(empId)
from employee
group by mngrId

-- for null mngr
Select EmpID, MngID, Title from Employee where mngrId=3

begin Tran
set rowcount 100 -- only 100 rows will get effected like top 100
Update employee
set loginId=null

--Alter query is faster than update
Alter table Employee
alter column LoginId nvarchar(256) null

Select mgrId, COUNT(empId), COUNT(LoginID), SUM(LoginID) --operator datatype
must not b varchar
from employee E
group by mngrId

Select mgrId, COUNT(empId), COUNT(isnull(LoginID, 'a'))
from employee E
group by mngrId

----------------------------------------------------
--------Mngr total emp count is >20-------
Select mgrId, COUNT(EmpId)
from Employee E
group by mngrId
having COUNT(empId)>20

-------------Another way---Derived Table-----
Select * from (Select mgrId, COUNT(EmpId) emp
from Employee E
group by mngrId)AA
where emp>20

---UNION---
select *
from
SalesLT.Customer a
inner join SalesLT.SalesOrderHeader CA on a.CustomerID = CA.CustomerID
inner join SalesLT.Address b on CA.AddressID = b.AddressID
where b.StateProvince= 'washington'

--Order byFirstName desc --Cannot use here--At end of query
UNION
select *
from
SalesLT.Customer a
where b.StateProvince= 'Texas'
Order by FirstName asc

---------------EXCEPT-----------------------

select *
from
SalesLT.Customer a
where b.StateProvince= 'washington'
EXCEPT -- same no of column and same datatype
select *
from
SalesLT.Customer a
where b.StateProvince= 'Texas'
Order by FirstName asc

----------Working with Intersect--------HW--------------------
========================
---------UnionAll----------
Create Table t1(i int)
insert into t1
select 1
union
select 2
union select 3

--
select distinct * from t1
select * from t1
union
select * from t1

select * from t1
union all
select * from t1
---
select distinct * from t1
select * from t1 -- Expensive performance
union
select * from t1

select i from t1
group by i
================================================

-------CUrrent Date Time

select GETDATE()
select LEFT('Pragya', 2) -- first 2
select Right('Pragya', 2)
select MONTH(getdate())
select DATEPART(M,getdate())
create table td(dt varchar(10))
Insert into td values('01/01/2011')
select * from td
select dt, CAST(dt as DATE),CAST(dt as datetime) from td

-- first day of month and last day of mnth with date-- HW
DECLARE @Today DATETIME
SELECT @Today = '8/25/2011'
SELECT DATEADD(dd,-(DAY(DATEADD(mm,1,@Today))-1),DATEADD(mm,0,@Today))
-----------------------------------------------------
SELECT DATEADD(dd, -DAY(DATEADD(m,1,@Today)), DATEADD(m,-2,@Today))
Value = 2007-03-31 00:00:00.000

My Sql concepts

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My Sql concepts