Tricky Questions

ORDER OF EXECUTION FOR INTEGRITY CHECK

1.       Identity Insert Check

2.      Nullability constraint

3.      Data type check

4.      Instead of trigger

5.      Primary key

6.      Check constraint

7.      Foreign key

8.     DML Execution (update statements)

9.      After Trigger

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FIND OUT # OF RECORDS FROM A TABLE

1.       SELECT rows FROM sys.sysindexes WHERE id = OBJECT_ID('UserManagement.CISFUser') AND indid < 2

2.      SELECT COUNT(*) FROM UserManagement.CISFUser

3.      SELECT COUNT(1) FROM UserManagement.CISFUser

4.      SP_SPACEUSED 'UserManagement.CISFUser'

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HOW TO CREATE SORTED VIEW

CREATE VIEW vw

AS

SELECT TOP 100 PERCENT * FROM TableName ORDER BY ColumnName

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COUNT(*) Vs. COUNT(ColumnName)

COUNT(*) à total number of rows from a table

COUNT(ColumnName) à total number of rows from a table WHERE ColumnName IS NOT NULL

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DELETE Vs. TRUNCATE

	Delete	Truncate
Speed	Slower	Faster
WHERE	Can be applied	Cannot be applied
IDENTITY	Cannot reset	Will reset
TRIGGER	Will fire	Won’t fire
Transaction Log	Will be logged	Won’t be logged
REFERENTIAL INTEGRITY	If Child table doesn’t have corresponding record from master table then it will allow	Will never ever allow if any referential integrity exists; no matter child table has record or not
Table Variable	Can be deleted	Cannot be truncated
CDC	Will allow	Won’t allow if CDC is enabled on table

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TEMP TABLE Vs. TABLE VARIABLE

	Temp Table	Table variable
Syntax	CREATE TABLE #TEMP (A INT)	DECLARE @TEMP TABLE (A INT)
Storage	Tempdb	Memory
Locking & Logging	Enabled	Disabled (improves performance)
Index	Possible	Not possible
Truncate	Possible	Not possible
Scope	Will be available in nested SP also	Will be limited
Dynamic Query	Will be allowed inside Dynamic Query	Won’t be allowed
When to use	When large number of records are there and which involves search. Index creation will help us	Small number of records are used. Logging and Locking won’t be there so will be faster
Final word	No theory has proved which one is good and which one is not. It all depends on requirement and number of records

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SELECT 3/4. WHAT IT WILL RETURN?

ZERO. If you say SELECT 3.0/4.0 then it will return 0.75

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HOW TO INSERT DESIRED VALUE IN IDENTITY COLUMN?

CREATE TABLE IdentityCheck (A INT IDENTITY(1,1), B VARCHAR(10))

INSERT INTO IdentityCheck (B) VALUES ('A'), ('B')

SET IDENTITY_INSERT IdentityCheck ON

INSERT INTO IdentityCheck (A,B) VALUES (5, 'C')

SET IDENTITY_INSERT IdentityCheck OFF

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HOW TO RESET IDENTITY TO DESIRED VALUE?

DBCC CHECKIDENT(IdentityCheck, 'RESEED',100)

Next value would be 101. Even you can reset to negative values or some already existing values. It won't throw any error but when you try to insert only that time it will check and it will throw error depends on other constraints like PK, Unique, Check etc..

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WHAT ARE THE DEFAULT SYS DATABASE AND THEIR PURPOSE?

MASTER --> It holds the information about all the databases and contains system objects

MSDB --> It contains information about sql agent, job, dts pckg & some replication information

TEMPDB --> It contains temporary SPs and Tables (global & local)

MODEL --> It is template database used in creation of any new database

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UNION Vs. UNION ALL

UNION will give only distinct values and UNION ALL will give all the values

However, output of all below 3 queries will be SAME.

-- Query 1

      SELECT 1

      UNION

      SELECT 1

      UNION ALL

      SELECT 2

-- Query 2

      SELECT 1

      UNION ALL

      SELECT 1

      UNION 

      SELECT 2

-- Query 3

      SELECT 1

      UNION

      SELECT 1

      UNION

      SELECT 2

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DIFFERENT WAYS TO IMPORT DATA

- BCP 

- BULK INSERT

- OPENROWSET
- OPENQUERY
- LINKED SERVER
- OPENDATASOURCE