SQL query optimization - sql

Question

I am trying to find out a script that can help me in Data Density of my DBs. the point is I already figure out the query and what I do need but the problem is the query takes for ever. it works find for small DBs, but that doesn't happen a lot.
So I am looking for kind of optimization or any ideas to help me.
the script:
DECLARE Cur CURSOR
FOR
SELECT DB_Name() AS DatabaseName
,s.[name] AS SchemaName
,t.[name] AS TableName
,c.[name] AS ColumnName
,'[' + DB_Name() + ']' + '.[' + s.NAME + '].' + '[' + T.NAME + ']' AS FullQualifiedTableName
,d.[name] AS DataType
FROM sys.schemas s
INNER JOIN sys.tables t ON s.schema_id = t.schema_id
INNER JOIN sys.columns c ON t.object_id = c.object_id
INNER JOIN sys.types d ON c.user_type_id = d.user_type_id
WHERE d.NAME LIKE '%int%'
OR d.NAME LIKE '%float%'
OR d.NAME LIKE '%decimal%'
OR d.NAME LIKE '%numeric%'
OR d.NAME LIKE '%real%'
OR d.NAME LIKE '%money%'
OR d.NAME LIKE '%date%'
OR d.NAME LIKE '%datetime%'
AND is_identity = 0
OPEN Cur
FETCH NEXT
FROM Cur
INTO #DatabaseName
,#SchemaName
,#TableName
,#ColumnName
,#FullyQualifiedTableName
,#DataType
WHILE ##FETCH_STATUS = 0 -- The FETCH statement was successful.
BEGIN
DECLARE #SQL VARCHAR(MAX) = NULL
SET #SQL = ' Select ''' + #DatabaseName + ''' AS DatabaseName, ''' +
#SchemaName + ''' AS TableName,
''' + #TableName + ''' AS SchemaName,
''' + #ColumnName + ''' AS ColumnName,
''' + #DataType + ''' AS ColumnName,
(Select MAX(' + #ColumnName + ') from ' + #FullyQualifiedTableName + ' with (nolock))
AS MaxValue,
(Select MIN(' + #ColumnName + ') from ' + #FullyQualifiedTableName + ' with (nolock))
AS MinValue,
(Select COUNT(*) from ' + #FullyQualifiedTableName + ' with (nolock))
AS CountValue,
(Select COUNT(*) from ' + #FullyQualifiedTableName + ' Where ' + #ColumnName + ' IS NOT NULL )
AS NotNULLCount,
(Select 0 from ' + #FullyQualifiedTableName + ')
AS DataDensity'
PRINT #SQL
The following script will give me the MAX, MIN, COUNT, NotNULLCount and the DATA DENSITY for every and each column form the declared types above. but u can imagine a DB with 70 tables and each table has 30-50 columns....
running this script will take for ever.

Answer 1

You should always try and avoid using cursors, this query will give you a list of select queries that you can copy and paste to get the data that you require. Note also I have removed the sub selects as they are not required:
SELECT 'Select ''' + DB_Name() + ''' AS DatabaseName, ''' + s.Name + ''' AS SchemaName, ''' + t.Name + ''' AS TableName, ''' + c.Name + ''' AS ColumnName, ''' + d.Name + ''' AS ColumnName,' +
'MAX([' + c.Name + ']) AS MaxValue,' +
'MIN([' + c.Name + ']) AS MinValue,' +
'COUNT(*) AS CountValue,' +
'COUNT([' + c.Name + ']) AS NotNullCount,' +
'CAST(COUNT(DISTINCT [' + c.name + ']) AS float) / COUNT([' + C.Name + ']) AS DataDensity ' +
'from [' + DB_Name() + '].[' + s.Name + '].[' + t.name + '] with (nolock)'
FROM sys.schemas s
INNER JOIN sys.tables t ON s.schema_id = t.schema_id
INNER JOIN sys.columns c ON t.object_id = c.object_id
INNER JOIN sys.types d ON c.user_type_id = d.user_type_id
WHERE d.NAME LIKE '%int%'
OR d.NAME LIKE '%float%'
OR d.NAME LIKE '%decimal%'
OR d.NAME LIKE '%numeric%'
OR d.NAME LIKE '%real%'
OR d.NAME LIKE '%money%'
OR d.NAME LIKE '%date%'
OR d.NAME LIKE '%datetime%'
AND is_identity = 0
This will give you a list of select statements in the following form:
Select 'MyDB' AS DatabaseName, 'dbo' AS SchemaName, 'MyTable' AS TableName, 'ID' AS ColumnName, 'int' AS ColumnName,MAX([ID]) AS MaxValue,MIN([ID]) AS MinValue,COUNT(*) AS CountValue,COUNT([ID]) AS NotNullCount,CAST(COUNT(DISTINCT [ID]) AS float) / COUNT([ID]) AS DataDensity from [MyDB].[dbo].[MyTable] with (nolock)
Of course SQL Server stores these sorts of statistics for useful columns, You can find which ones it has be using:
EXEC SP_HELPSTATS 'MyTable', 'ALL'
Then using the list of statistics returned such as:
_WA_Sys_00000014_004FB3FB ID
to get the actual stats using:
DBCC SHOW_STATISTICS('MyTable','_WA_Sys_00000002_004FB3FB')
This will return data like:
Name Updated Rows Rows Sampled Steps Density Average key length String Index Filter Expression Unfiltered Rows
_WA_Sys_00000002_004FB3FB Jan 8 2017 8:01PM 16535 16535 200 0.2493151 4.459389 NO NULL 16535
and
All density Average Length Columns
0.0006038647 4.459389 EffectiveDate
and another rowset showing a histogram of values.
You can automatically generate these DBCC commands using:
SELECT 'DBCC SHOW_STATISTICS([' + OBJECT_NAME(s.object_Id) + '],''' + s.Name + ''')'
FROM sys.stats s
INNER JOIN sys.stats_columns sc
ON s.object_id = sc.object_id AND s.stats_id = sc.stats_id
INNER JOIN sys.columns c
ON sc.object_id = c.object_id AND sc.column_id = c.column_id
WHERE s.Name LIKE '_WA%'
ORDER BY s.stats_id, sc.column_id;