Find Most executed queries

SELECT TOP 50
QueryState.execution_count
,OBJECT_NAME(objectid)
,query_text = SUBSTRING(
qt.text,
QueryState.statement_start_offset/2,
(CASE WHEN QueryState.statement_end_offset = -1
THEN len(convert(nvarchar(max), qt.text)) * 2
ELSE QueryState.statement_end_offset
END - QueryState.statement_start_offset)/2)
,qt.dbid
,dbname = db_name(qt.dbid)
,qt.objectid
FROM sys.dm_exec_query_stats QueryState
CROSS APPLY sys.dm_exec_sql_text(QueryState.sql_handle) as qt
ORDER BY QueryState.execution_count DESC

Get all queries running against any specific table

/*

Get list of all queries hitting any specific tables

*/

SELECT DISTINCT TOP 100

ProcedureName = OBJECT_SCHEMA_NAME(sqlTxt.objectid) + '.' + OBJECT_NAME(sqlTxt.objectid)

,SQLStatement = SUBSTRING(

sqlTxt.Text

,(QueryState.statement_start_offset/2)+1

,CASE QueryState.statement_end_offset

WHEN -1 THEN DATALENGTH(sqlTxt.text)

ELSE QueryState.statement_end_offset

END - (QueryState.statement_start_offset/2) + 1

)

,DiskReads = QueryState.total_physical_reads --- Disk reads

,MemoryReads = QueryState.total_logical_reads --–Logical Reads are memory reads

,ExecutionCount = QueryState.execution_count --Execution Count

,CPUTime = QueryState.total_worker_time  --CPU Time

,DiskWaitAndCPUTime = QueryState.total_elapsed_time

,MemoryWrites = QueryState.max_logical_writes

,DateCached = QueryState.creation_time

,DatabaseName = DB_Name(sqlTxt.dbid) --Database name

,LastExecutionTime = QueryState.last_execution_time

,cte.*

FROM sys.dm_exec_query_stats AS QueryState

CROSS APPLY sys.dm_exec_sql_text(QueryState.sql_handle) AS sqlTxt

CROSS APPLY sys.dm_sql_referenced_entities(

OBJECT_SCHEMA_NAME(sqlTxt.objectid) + '.' + OBJECT_NAME(sqlTxt.objectid)

, 'OBJECT'

) cte

WHERE sqlTxt.dbid = db_id() --Get detail for current database

AND cte.referenced_schema_name + '.' + cte.referenced_entity_name = 'dbo.tblEmployee'

Missing index with create statements

Missing index :- Scripts will help you to get all the missing index and prepare script for new index.

/*
Description:- This Query will provide you detail of missing indexes on a table and also 
 prepare sql script for new index
*/
SELECT
DISTINCT
   @@SERVERNAME AS [ServerName]
   , DB_NAME() AS [DatabaseName]
   , SCHEMA_NAME([systemObject].[schema_id]) AS [SchemaName]
,[systemObject].Object_ID AS ObjectID
   , [systemObject].[name] AS [ObjectName]
   , CASE [systemObject].[type]
      WHEN 'U' THEN 'Table'
      WHEN 'V' THEN 'View'
      ELSE 'Unknown'
     END AS [ObjectType]
   , [MissingIndexDetail].[equality_columns] AS [EqualityColumns]
   , [MissingIndexDetail].[inequality_columns] AS [InequalityColumns]
   , [MissingIndexDetail].[included_columns] AS [IncludedColumns]
   , [MissingIndexGroupState].[user_seeks] AS [ExpectedIndexSeeksByUserQueries]
   , [MissingIndexGroupState].[user_scans] AS [ExpectedIndexScansByUserQueries]
   , [MissingIndexGroupState].[last_user_seek] AS [ExpectedLastIndexSeekByUserQueries]
   , [MissingIndexGroupState].[last_user_scan] AS [ExpectedLastIndexScanByUserQueries]
   , [MissingIndexGroupState].[avg_total_user_cost] AS [ExpectedAvgUserQueriesCostReduction]
   , [MissingIndexGroupState].[avg_user_impact] AS [ExpectedAvgUserQueriesBenefitPct],
   IndexName='[ix_' + tbl.name + N'_' 
                    + REPLACE(REPLACE(REPLACE(REPLACE(
                        ISNULL(equality_columns,N'')+ 
                        CASE WHEN equality_columns IS NOT NULL AND inequality_columns IS NOT NULL THEN N'_' ELSE N'' END
                        + ISNULL(inequality_columns,''),',','')
                        ,'[',''),']',''),' ','_') 
                    + CASE WHEN included_columns IS NOT NULL THEN N'_includes' ELSE N'' END + N']' ,

     IndexCreateScripts=N'CREATE INDEX [ix_' + tbl.name + N'_' 
                    + REPLACE(REPLACE(REPLACE(REPLACE(
                        ISNULL(equality_columns,N'')+ 
                        CASE WHEN equality_columns IS NOT NULL AND inequality_columns IS NOT NULL THEN N'_' ELSE N'' END
                        + ISNULL(inequality_columns,''),',','')
                        ,'[',''),']',''),' ','_') 
                    + CASE WHEN included_columns IS NOT NULL THEN N'_includes' ELSE N'' END + N'] ON ' 
                    + [statement] + N' (' + ISNULL(equality_columns,N'')
                    + CASE WHEN equality_columns IS NOT NULL AND inequality_columns IS NOT NULL THEN N', ' ELSE N'' END
                    + CASE WHEN inequality_columns IS NOT NULL THEN inequality_columns ELSE N'' END + 
                    ') ' + CASE WHEN included_columns IS NOT NULL THEN N' INCLUDE (' + included_columns + N')' ELSE N'' END
                    + N' WITH (' 
                        + N'FILLFACTOR=80, ONLINE=ON' 
                    + N')'
                    + N';'
FROM 
   [sys].[dm_db_missing_index_details] AS [MissingIndexDetail]
   CROSS APPLY sys.dm_db_missing_index_columns  ([MissingIndexDetail].index_handle)
   LEFT JOIN [sys].[dm_db_missing_index_groups] AS [MissingIndexGroup]
      ON [MissingIndexDetail].[index_handle] = [MissingIndexGroup].[index_handle]
   LEFT JOIN [sys].[dm_db_missing_index_group_stats] AS [MissingIndexGroupState]
      ON [MissingIndexGroup].[index_group_handle] = [MissingIndexGroupState].[group_handle]
   INNER JOIN [sys].[objects] AS [systemObject]
      ON [MissingIndexDetail].[object_id] = [systemObject].[object_id]
inner join sys.databases db on [MissingIndexDetail].database_id=db.database_id
inner join sys.tables tbl on [systemObject].object_id=tbl.object_id
WHERE
   [MissingIndexDetail].[database_id] = DB_ID()  -- Look in the Current Database
   AND [systemObject].[type] IN ('U','V')     -- Look in Tables & Views
   AND [systemObject].[is_ms_shipped] = 0x0   -- Exclude System Generated Objects
   --and( tbl.name like '%Accounting%' or tbl.name like '%treasury%') --Add table name for filter
--and [MissingIndexGroupState].[avg_user_impact]>=50; -- filter impact percentage 


go

How we can determine table column dependencies within a SQL database?

I came a situation during some analysis where i had to figure out all dependency of a column across database. This also required when we do some changes on table columns and wanted to know the impact of such changes. One way is that  we can use SYSCOMMENTS table.  It is a table which contains entries for each views, rules, default, trigger, CHECK constraint, DEFAULT constraint, and stored procedure. The column TEXT in the syscomments table contains the actual code for all these objects, and knowing it you can write a code to check the dependencies. I am explaining different approach.

/* Table Name for which we need to find the dependency of columns.*/

Declare @TableName varchar(max)='tblSupplierRequestOrder'

/* Column name for which we need to find the dependnecy in a database*/

Declare @ColumnName varchar(max)='OrderDate'

select  OBJECT_NAME(k.parent_object_id) as parentTableName

          , c1.name as parentColumn

          , OBJECT_NAME(k.referenced_object_id) as referencedTableName

          , c2.name as referencedColumn

    from    sys.foreign_keys k

            inner join sys.foreign_key_columns f

              on  f.parent_object_id = k.parent_object_id

            inner join sys.columns c1

              on  c1.column_id = f.parent_column_id

              and c1.object_id = k.parent_object_id

            inner join sys.columns c2

              on  c2.column_id = f.referenced_column_id

              and c2.object_id = k.referenced_object_id

    where   c2.name = @ColumnName

    and     OBJECT_NAME(k.referenced_object_id) =@TableName

Column and table constraints

Column and Table Constraints

Constraints can be column constraints or table constraints.

A column constraint is specified as part of a column definition and applies only to that column.

A table constraint is declared independently from a column definition and can apply to more than one column in a table. Table constraints must be used when more than one column must be included in a constraint.

For example, if a table has two or more columns in the primary key, you must use a table constraint to include both columns in the primary key. Consider a table that records events occurring in a system.

A number of different event can occur in different time or same time but assuming no same event occur in same time and same type.

This can be enforced in the table by including both the event_type and event_time columns in a two-column primary key, as shown in the following example.

CREATE TABLE System_process

   (event_typeID   int,

   event_time   datetime,

   event_site   char(50),

   event_desc   char(1024),

CONSTRAINT event_key PRIMARY KEY (event_typeID , event_time) )

What is Constraints in TSQL?

Constraints let you define the way the Database Engine automatically enforces the integrity of a database. Constraints define rules regarding the values allowed in columns and are the standard mechanism for enforcing integrity.Constraints is preferred to using DML Triggers, rules, and defaults. The query optimizer also uses constraint definitions to build high-performance query execution plans.

Types of Constraints.

·         NOT NULL, This specify that column does not access NULL values.

·         CHECK constraints enforce domain integrity by limiting the values that can be put in a column. A check constraint can be Boolean values (True, false or unknown). We can add search condition which will be applied while we do insert or update operation on a column. This also enforce that inserted or updated values must be in range which is specified within check.

CREATE TABLE Employee

   (

   Employee_id     bigint PRIMARY KEY,

   Employee_name   varchar(max),

   Emp_address     varchar(max),

   Emp_basic_pay   money,

   CONSTRAINT chk_id CHECK (Employee_id BETWEEN 100 and 1000000 )

   )

·         UNIQUE constraints enforce the uniqueness of the values in a set of columns. This enforce no two rows in a table can have same value for the columns. Primary keys also enforce uniqueness, but primary keys do not allow NULL as one of the unique values.

·     PRIMARY KEY constraints identify the column or set of columns that have values that uniquely identify a row in a table. No two rows in a table can have the same primary key value. You cannot enter NULL for any column in a primary key.

CREATE TABLE Employee

   (

   Employee_id     bigint PRIMARY KEY,

   Employee_name   varchar(max),

   Emp_address     varchar(max),

‘   Emp_basic_pay   money,

   CONSTRAINT chk_id CHECK (Employee_id BETWEEN 100 and 1000000 )

   )

•          FOREIGN KEY constraints identify and enforce the relationships between tables.

A foreign key in one table points to a candidate key in another table. (A column or combination    of columns that qualify as a primary key value is referred to as a candidate key.)

CREATE TABLE order_part

  (

order_nmbr      int,

part_nmbr      int

             FOREIGN KEY REFERENCES part_sample(part_nmbr)

            ON DELETE NO ACTION,

          qty_ordered      int

);

GO

You cannot insert a row with a foreign key value, except NULL, if there is no candidate key with that value. The ON DELETE clause controls what actions are taken when you try to delete a row to which existing foreign keys point.

 The ON DELETE clause has the following options:

a.  NO ACTION specifies that the deletion fails with an error.

b.  CASCADE specifies that all the rows with foreign keys pointing to the deleted row are also  deleted.

c.  SET NULL specifies that all rows with foreign keys pointing to the deleted row are set to NULL.

d.  SET DEFAULT specifies that all rows with foreign keys pointing to the deleted row are set to their default value

The ON UPDATE clause defines the actions that are taken if you try to update a candidate key value to which existing foreign keys point. This clause also supports the NO ACTION, CASCADE, SET NULL and SET DEFAULT options.