Measure-DbColumn.ps1

<#
.SYNOPSIS
Provides statistics about SQL Server column data.

.INPUTS
Microsoft.SqlServer.Management.Smo.Column to calculate statistics for,
or Microsoft.SqlServer.Management.Smo.Table to select a column from by name.

.OUTPUTS
System.Management.Automation.PSCustomObject that describes the column:

* ColumnName
* SqlType
* NullValues
* IsUnique
* UniqueValues
* MinimumValue
* MaximumValue
* MeanAverage
* ModeAverage
* Variance
* StandardDeviation
* additonal properties, depending on type

.LINK
https://www.powershellgallery.com/packages/SqlServer/

.LINK
https://dbatools.io/

.LINK
https://wikipedia.org/wiki/Windows1252

.EXAMPLE
$table = Get-DbaDbTable SqlServerName -Database DbName -Table TableName; Measure-DbColumn.ps1 $table.Columns['record_id']

ColumnName        : record_id
SqlType           : int
NullValues        : 0
IsUnique          : True
UniqueValues      : 43
MinimumValue      : 2
MaximumValue      : 56
MeanAverage       : 28
ModeAverage       : 28
Variance          : 290.330011074197
StandardDeviation : 17.0390730696889

.EXAMPLE
Get-DbaDbTable SqlServerName -Database DbName -Table TableName |Measure-DbColumn.ps1 surname

ColumnName         : surname
SqlType            : varchar(40)
NullValues         : 0
IsUnique           : False
UniqueValues       : 72281
MinimumValue       :  AARONSON
MaximumValue       : ZYKOWSKI
MostCommonValue    : SMITH
MininumLength      : 1
MaximumLength      : 40
HasLeadingSpaces   : True
HasTrailingSpaces  : False
HasControlChars    : False
HasWindows1252     : False
HasUnicode         : False
HasNonAscii7       : False
HasNonAlphanumeric : True

.EXAMPLE
Get-DbaDbTable '(localdb)\ProjectsV13' -database AdventureWorks2016 -Table Sales.SalesOrderHeader |Measure-DbColumn.ps1 OrderDate

ColumnName      : OrderDate
SqlType         : datetime
Values          : 31465
NullValues      : 0
IsUnique        : False
IsDateOnly      : True
DateOnlyValues  : 31465
DateTimeValues  : 0
UniqueValues    : 1124
MostCommonValue : 03/31/2014 00:00:00
MinimumValue    : 05/31/2011 00:00:00
MaximumValue    : 06/30/2014 00:00:00
ModeAverage     : 03/31/2014 00:00:00
MeanYear        : 2013
ModeYear        : 2013
MeanMonth       : January
ModeMonth       : May
MeanDayOfWeek   : Thursday
ModeDayOfWeek   : Monday
MeanDayOfMonth  : 16
Sunday          : 4444
Monday          : 4875
Tuesday         : 4482
Wednesday       : 4591
Thursday        : 4346
Friday          : 4244
Saturday        : 4483
January         : 2877
Febuary         : 2300
March           : 3144
April           : 2812
May             : 3175
June            : 2189
July            : 2356
August          : 2324
September       : 2300
October         : 2616
November        : 2716
December        : 2656
#>

#Requires -Version 3
#Requires -Module SqlServer
[CmdletBinding(ConfirmImpact='Medium')][OutputType([Management.Automation.PSCustomObject])] Param(
# An SMO column object associated to the database column to examine.
[Parameter(Position=0,Mandatory=$true,ValueFromPipeline=$true,ParameterSetName='Column')]
[Microsoft.SqlServer.Management.Smo.Column] $Column,
# The name of the column to examine in the table associated with the SMO Table object.
[Parameter(Position=0,Mandatory=$true,ParameterSetName='ColumnName')][string] $ColumnName,
# An SMO table object associated to the database to examine.
[Parameter(Position=1,Mandatory=$true,ValueFromPipeline=$true,ParameterSetName='ColumnName')]
[Microsoft.SqlServer.Management.Smo.Table] $Table,
<#
Conditions to be provided as a SQL WHERE clause to filter the column values to examine.
Useful for databases that implement "soft deletes" as specific field values.
#>
[string] $Condition
)
Begin
{
    $SOQ = @'
select '{2}' ColumnName,
       '{3}' SqlType,
'@
    $EOQ = if(!$Condition) {' from [{0}].[{1}];'} else {" from [{0}].[{1}] where $Condition ;"}
    $query = @{
        Numeric = @"
  with TopValues as (
select top 1 with ties [{2}] value, count(*) #
  from [{0}].[{1}]
 group by [{2}]
 order by # desc
),     MedianValue as (
select max(value) value
  from (select top 50 percent [{2}] value from [{0}].[{1}] order by value) a
 union
select min(value)
  from (select top 50 percent [{2}] value from [{0}].[{1}] order by value desc) b
)
$SOQ
       count([{2}]) [Values],
       sum(case when [{2}] is null then 1 else 0 end) NullValues,
       cast(case when count(*) = count(distinct [{2}]) then 1 else 0 end as bit) IsUnique,
       count(distinct [{2}]) UniqueValues,
       min([{2}]) MinimumValue,
       max([{2}]) MaximumValue,
       avg(cast([{2}] as real)) MeanAverage,
       (select avg(cast(value as real)) from MedianValue) MedianAverage,
       (select avg(cast(value as real)) from TopValues) ModeAverage,
       var([{2}]) Variance,
       stdev([{2}]) StandardDeviation
$EOQ
"@
        DateTime = @"
  with TopValues as (
select top 1 [{2}] value, count(*) #
  from [{0}].[{1}]
 group by [{2}]
 order by # desc
),     MedianValue as (
select max(a.value) value
  from (select top 50 percent [{2}] value from [{0}].[{1}] order by value) a
 union
select min(b.value)
  from (select top 50 percent [{2}] value from [{0}].[{1}] order by value desc) b
),     DateOnlyCount as (
select count(*) #
  from [{0}].[{1}]
 where [{2}] = cast([{2}] as date)
),     TopYears as (
select top 1 Year([{2}]) [year], count(*) #
  from [{0}].[{1}]
 group by Year([{2}])
 order by # desc
),     TopMonths as (
select top 1 datename(month,[{2}]) [month], count(*) #
  from [{0}].[{1}]
 group by datename(month,[{2}])
 order by # desc
),     TopDaysOfWeek as (
select top 1 datename(dw,[{2}]) [dayofweek], count(*) #
  from [{0}].[{1}]
 group by datename(dw,[{2}])
 order by # desc
),     TopDays as (
select top 1 Day([{2}]) [day], count(*) #
  from [{0}].[{1}]
 group by Day([{2}])
 order by # desc
)
$SOQ
       count([{2}]) [Values],
       sum(case when [{2}] is null then 1 else 0 end) NullValues,
       cast(case when count(*) = count(distinct [{2}]) then 1 else 0 end as bit) IsUnique,
       cast(case count([{2}]) when (select # from DateOnlyCount) then 1 else 0 end as bit) IsDateOnly,
       (select # from DateOnlyCount) DateOnlyValues,
       count([{2}]) - (select # from DateOnlyCount) DateTimeValues,
       count(distinct [{2}]) UniqueValues,
       (select top 1 value from TopValues) MostCommonValue,
       min([{2}]) MinimumValue,
       max([{2}]) MaximumValue,
       --dateadd(seconds,'1970-01-01',avg(cast(datediff(second,'1970-01-01',[{2}]) as real))) MeanAverage,
       --(select dateadd(seconds,avg([{2}]),'1970-01-01') from TopValues) MedianAverage,
       (select value from TopValues) ModeAverage,
       cast(avg(cast(Year([{2}]) as real)) as int) MeanYear,
       (select [year] from TopYears) ModeYear,
       datename(month,avg(Month([{2}]))) MeanMonth,
       (select [month] from TopMonths) ModeMonth,
       datename(dw,avg(datepart(dw,[{2}]))) MeanDayOfWeek,
       (select [dayofweek] from TopDaysOfWeek) ModeDayOfWeek,
       avg(Day([{2}])) MeanDayOfMonth,
       sum(case datepart(dw,[{2}]) when 1 then 1 end) Sunday,
       sum(case datepart(dw,[{2}]) when 2 then 1 end) Monday,
       sum(case datepart(dw,[{2}]) when 3 then 1 end) Tuesday,
       sum(case datepart(dw,[{2}]) when 4 then 1 end) Wednesday,
       sum(case datepart(dw,[{2}]) when 5 then 1 end) Thursday,
       sum(case datepart(dw,[{2}]) when 6 then 1 end) Friday,
       sum(case datepart(dw,[{2}]) when 7 then 1 end) Saturday,
       sum(case datepart(m,[{2}]) when 1 then 1 end) January,
       sum(case datepart(m,[{2}]) when 2 then 1 end) Febuary,
       sum(case datepart(m,[{2}]) when 3 then 1 end) March,
       sum(case datepart(m,[{2}]) when 4 then 1 end) April,
       sum(case datepart(m,[{2}]) when 5 then 1 end) May,
       sum(case datepart(m,[{2}]) when 6 then 1 end) June,
       sum(case datepart(m,[{2}]) when 7 then 1 end) July,
       sum(case datepart(m,[{2}]) when 8 then 1 end) August,
       sum(case datepart(m,[{2}]) when 9 then 1 end) September,
       sum(case datepart(m,[{2}]) when 10 then 1 end) October,
       sum(case datepart(m,[{2}]) when 11 then 1 end) November,
       sum(case datepart(m,[{2}]) when 12 then 1 end) December
$EOQ
"@
        Temporal = @"
  with TopValues as (
select top 1 [{2}] value, count(*) #
  from [{0}].[{1}]
 group by [{2}]
 order by # desc
)
$SOQ
       count([{2}]) [Values],
       sum(case when [{2}] is null then 1 else 0 end) NullValues,
       cast(case when count(*) = count(distinct [{2}]) then 1 else 0 end as bit) IsUnique,
       count(distinct [{2}]) UniqueValues,
       (select top 1 value from TopValues) MostCommonValue,
       min([{2}]) MinimumValue,
       max([{2}]) MaximumValue
$EOQ
"@
        String = @"
  with TopValues as (
select top 1 [{2}] value, count(*) #
  from [{0}].[{1}]
 group by [{2}]
 order by # desc
)
$SOQ
       count([{2}]) [Values],
       sum(case when [{2}] is null then 1 else 0 end) NullValues,
       cast(case when count(*) = count(distinct [{2}]) then 1 else 0 end as bit) IsUnique,
       count(distinct [{2}]) UniqueValues,
       min([{2}]) MinimumValue,
       max([{2}]) MaximumValue,
       (select top 1 value from TopValues) MostCommonValue,
       min(len([{2}])) MininumLength,
       max(len([{2}])) MaximumLength,
       cast(case when exists (select top 1 * from [{0}].[{1}] where [{2}] <> ltrim([{2}])) then 1 else 0 end as bit) HasLeadingSpaces,
       cast(case when exists (select top 1 * from [{0}].[{1}] where [{2}] <> rtrim([{2}])) then 1 else 0 end as bit) HasTrailingSpaces,
       cast(case when exists (select top 1 * from [{0}].[{1}] where [{2}] like '%'+char(0x09)+'%') then 1 else 0 end as bit) HasTabs,
       cast(case when exists (select top 1 * from [{0}].[{1}] where [{2}]
           like '%[' + char(0x00) + '-' + char(0x1F) + ']%') then 1 else 0 end as bit) HasControlChars,
       cast(case when exists (select top 1 * from [{0}].[{1}] where [{2}]
           like '%[€‚ƒ„…†‡ˆ‰Š‹ŒŽ‘’“”•–—˜™š›œžŸ]%') then 1 else 0 end as bit) HasWindows1252Conflicts,
       cast(case when exists (select top 1 * from [{0}].[{1}] where [{2}] collate SQL_Latin1_General_CP437_BIN
           <> cast([{2}] as varchar(max)) collate SQL_Latin1_General_CP437_BIN) then 1 else 0 end as bit) HasUnicode,
       cast(case when exists (select top 1 * from [{0}].[{1}] where [{2}] collate SQL_Latin1_General_CP437_BIN
           like '%[^' + char(0x00) + '-~]%') then 1 else 0 end as bit) HasNonAscii7,
       cast(case when exists (select top 1 * from [{0}].[{1}] where ltrim(rtrim([{2}])) like '%[^0-9A-Za-z_]%') then 1 else 0 end as bit) HasNonAlphanumeric
$EOQ
"@
        VariableLength = @"
$SOQ
       count([{2}]) [Values],
       sum(case when [{2}] is null then 1 else 0 end) NullValues,
       cast(case when count(*) = count(distinct [{2}]) then 1 else 0 end as bit) IsUnique,
       count(distinct [{2}]) UniqueValues,
       min(len([{2}])) MininumLength,
       max(len([{2}])) MaximumLength
$EOQ
"@
        Other = @"
$SOQ
       count([{2}]) Values,
       sum(case when [{2}] is null then 1 else 0 end) NullValues
$EOQ
"@
    }
    $typeinfo = @{
        bigint           = @('Numeric','{0}')
        binary           = @('VariableLength','{0}({1})')
        bit              = @('Other','{0}')
        char             = @('String','{0}({1})')
        cursor           = @('Other','{0}')
        date             = @('Temporal','{0}')
        datetime         = @('DateTime','{0}')
        datetime2        = @('DateTime','{0}({3})')
        datetimeoffset   = @('DateTime','{0}({3})')
        decimal          = @('Numeric','{0}({2},{3})')
        float            = @('Numeric','{0}')
        geography        = @('Other','{0}')
        geometry         = @('Other','{0}')
        hierarchyid      = @('Other','{0}')
        image            = @('Other','{0}')
        int              = @('Numeric','{0}')
        money            = @('Numeric','{0}')
        nchar            = @('String','{0}({1})')
        ntext            = @('Other','{0}')
        numeric          = @('Numeric','{0}({2},{3})')
        nvarchar         = @('String','{0}({1:0;max})')
        real             = @('Numeric','{0}')
        rowversion       = @('Other','{0}')
        smalldatetime    = @('DateTime','{0}')
        smallint         = @('Numeric','{0}')
        smallmoney       = @('Numeric','{0}')
        sql_variant      = @('VariableLength','{0}')
        table            = @('Other','{0}')
        text             = @('Other','{0}')
        time             = @('Temporal','{0}')
        tinyint          = @('Numeric','{0}')
        uniqueidentifier = @('Other','{0}')
        varbinary        = @('VariableLength','{0}({1:0;max})')
        varchar          = @('String','{0}({1:0;max})')
        xml              = @('VariableLength','{0}')
    }
}
Process
{
	if($Column) {$ColumnName = $Column.Name}
	else
	{
		$Column = $Table.Columns[$ColumnName]
		if(!$Column) {Stop-ThrowError.ps1 "Column '$ColumnName' not found in table '$($Table.Name)'" -Argument ColumnName}
	}
    $datatype = $Column.DataType
    $querytype,$typefmt = $typeinfo[$datatype.Name]
    $table = $Column.Parent
	$fqtn = "$($table.Parent.Parent.Name).$($table.Parent.Name).$($table.Name)"
	$sql = $query[$querytype] -f $table.Schema,$table.Name,$ColumnName,
		($typefmt -f $datatype.Name,$datatype.MaximumLength,$datatype.NumericPrecision,$datatype.NumericScale)
	Write-Verbose "SQL: $sql"
    @{
        Query = $sql
        Database = $table.Parent.Name
        ServerInstance = $table.Parent.Parent.Name
	} |
        where {$PSCmdlet.ShouldProcess("column $fqtn.$ColumnName","query $($table.RowCount) rows")} |
        foreach {Invoke-Sqlcmd @_} |
        ConvertFrom-DataRow.ps1
}