sql server - SQL query optimization -


i trying find out script can me in data density of dbs. point figure out query , need problem query takes ever. works find small dbs, doesn't happen lot. looking kind of optimization or ideas me. script:

declare cur cursor select db_name() databasename ,s.[name] schemaname ,t.[name] tablename ,c.[name] columnname ,'[' + db_name() + ']' + '.[' + s.name + '].' + '[' + t.name + ']' fullqualifiedtablename ,d.[name] datatype 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  d.name '%int%' or d.name '%float%' or d.name '%decimal%' or d.name '%numeric%' or d.name '%real%' or d.name '%money%' or d.name '%date%' or d.name '%datetime%'  , is_identity = 0  open cur  fetch next cur @databasename ,@schemaname ,@tablename ,@columnname ,@fullyqualifiedtablename ,@datatype   while @@fetch_status = 0 -- fetch statement successful. begin declare @sql varchar(max) = null  set @sql = ' select ''' + @databasename + ''' databasename, ''' +  @schemaname + ''' tablename,   ''' + @tablename + ''' schemaname,   ''' + @columnname + ''' columnname,   ''' + @datatype + ''' columnname,    (select max(' + @columnname + ') ' + @fullyqualifiedtablename + ' (nolock))    maxvalue,   (select min(' + @columnname + ') ' + @fullyqualifiedtablename + ' (nolock))    minvalue,   (select count(*) ' + @fullyqualifiedtablename + '   (nolock))    countvalue,   (select count(*) ' + @fullyqualifiedtablename + ' ' + @columnname + ' not null )    notnullcount,   (select 0 ' + @fullyqualifiedtablename + ')    datadensity'  print @sql

the following script give me max, min, count, notnullcount , data density every , each column form declared types above. u can imagine db 70 tables , each table has 30-50 columns.... running script take ever.

you should try , avoid using cursors, query give list of select queries can copy , paste data require. note have removed sub selects not required:

select 'select ''' + db_name()  + ''' databasename, ''' + s.name + ''' schemaname,  ''' + t.name + ''' tablename,  ''' + c.name + ''' columnname,  ''' + d.name + ''' columnname,' +  'max([' + c.name + ']) maxvalue,' +  'min([' + c.name + '])  minvalue,' +  'count(*)  countvalue,' +  'count([' + c.name + '])  notnullcount,' +   'cast(count(distinct [' + c.name + ']) float) / count([' + c.name + '])  datadensity ' +   'from [' +  db_name() + '].[' + s.name + '].[' + t.name + '] (nolock)' 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  d.name '%int%' or d.name '%float%' or d.name '%decimal%' or d.name '%numeric%' or d.name '%real%' or d.name '%money%' or d.name '%date%' or d.name '%datetime%' , is_identity = 0

this give list of select statements in following form:

select 'mydb' databasename, 'dbo' schemaname,  'mytable' tablename,  'id' columnname,  'int' columnname,max([id]) maxvalue,min([id])  minvalue,count(*)  countvalue,count([id])  notnullcount,cast(count(distinct [id]) float) / count([id])  datadensity [mydb].[dbo].[mytable] (nolock)

of course sql server stores these sorts of statistics useful columns, can find ones has using:

exec sp_helpstats 'mytable', 'all'

then using list of statistics returned such as:

_wa_sys_00000014_004fb3fb   id

to actual stats using:

dbcc show_statistics('mytable','_wa_sys_00000002_004fb3fb')

this 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 rowset showing histogram of values.

you can automatically generate these dbcc commands using:

select  'dbcc show_statistics([' + object_name(s.object_id) + '],''' +  s.name + ''')' sys.stats s    inner join sys.stats_columns sc     on s.object_id = sc.object_id , s.stats_id = sc.stats_id   inner join sys.columns c     on sc.object_id = c.object_id , sc.column_id = c.column_id s.name '_wa%' order s.stats_id, sc.column_id;

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