Posts Tagged ‘T-SQL’

Create SQL for Temp Table

Sometimes it is really useful to work with temp tables and to create them up front rather than using ‘Select Into’, but they can be a pain create for a couple of reasons:

  1. The temp table has loads of columns and you really don’t want to sit and type them all in.
  2. You are not aware of the structure of the source data.

The following stored procedure takes the hassle away. Merely select some data (use Select Top(0) for speed) into a temp table that has the desired structure and then execute the stored procedure below to generate the SQL will create the temp table.

Anyway, here’s the code.


Create Procedure dbo.GenerateTempTableSQL
    Given a temp table the sql required to create a new temp table of the same
    structure is generated.
    This is useful during development to select into a temp table and
    then generate the code that could be used to create the temp table.
        The name of the temp table to use as the template the generate the SQL
    @output_temp_table_name [optional: @input_temp_table_name]
        The name of the table that is used in the create table script. If
        left as null, then the @input_temp_table_name will be used.
    @database_collation [optional: current database collation]
        The collation to use for char based columns.
    16-Oct-2015 S.Wilber
    09-Nov-2015 S.Wilber
        Updated to include # in temp table name if it had been ommitted.
    14-Jul-2016 S.Wilber
        Updated to work from temp tables instead of permanent tables
    @input_temp_table_name sysname
   ,@output_temp_table_name sysname = null
   ,@database_collation sysname = null

-- declare constants

-- declare variables
Declare     @sql nvarchar(max)

-- table to store the columns
If Object_ID('tempdb..#temp') Is Not Null Drop Table #temp
Create Table #temp
    column_id int not null
   ,column_name nvarchar(130) null
   ,type_name nvarchar(130) not null
   ,max_length smallint not null
   ,scale tinyint not null
   ,[precision] tinyint not null
   ,is_nullable bit null
   ,collation_name sysname null

-- table to store the generated SQL
Declare     @output_sql table (line_id int identity(1, 1), sql nvarchar(max))
Declare     @object_id int

-- set the output name to be the input name if it is null or blank or whitespace
If NullIf(LTrim(RTrim(@output_temp_table_name)), '') Is Null Set @output_temp_table_name = @input_temp_table_name

-- set the collation if it's not set
If NullIf(LTrim(RTrim(@database_collation)), '') Is Null Set @database_collation = Cast(DatabasePropertyEx(db_name(), 'collation') As nvarchar(128))

-- add a # to the input temp table name if it does not already start with #
If Left(@input_temp_table_name, 1) != '#' Set @input_temp_table_name = '#' + @input_temp_table_name

-- add a # to the output temp table name if it does not already start with #
If Left(@output_temp_table_name, 1) != '#' Set @output_temp_table_name = '#' + @output_temp_table_name

-- get the object id
Select      @object_id = Object_ID('tempdb..' + @input_temp_table_name)

If @object_id Is Null
    RaisError('''%s'' cannot be found.', 11, 1, @input_temp_table_name)

-- generate the sql
Insert      @output_sql (sql)
Select      'If Object_ID(''tempdb..' + @output_temp_table_name + ''') Is Not Null Drop Table ' + @output_temp_table_name

Insert      @output_sql (sql)
Select      'Create Table ' + @output_temp_table_name

Insert      @output_sql (sql)
Select      '('

Insert      #temp (column_id, column_name, type_name, max_length, scale, precision, is_nullable, collation_name)
Select      c.column_id
           ,Case When CharIndex('|' + + '|', @reserved_words) != 0 Then '[' + + ']' Else End As column_name
           ,Case When CharIndex('|' + + '|', @reserved_words) != 0 Then '[' + + ']' Else End As type_name
From        tempdb.sys.objects o
Inner Join  tempdb.sys.schemas s On (s.schema_id = o.schema_id)
Inner Join  tempdb.sys.columns c On (o.object_id = c.object_id)
Inner Join  tempdb.sys.types t On (t.user_type_id = c.user_type_id)
Where       o.object_id = @object_id

Insert      @output_sql (sql)
Select      Case When column_id = 1 Then space(4) Else space(3) + ',' End
          + column_name + ' '
          + type_name
          + Case
                When Lower(type_name) In ('datetimeoffset', 'datetime2', 'time') Then
                    '(' + Cast(IsNull(c.scale, '') As varchar(10)) + ')'
                When Lower(type_name) In ('decimal', 'numeric') Then
                    '(' + Cast(IsNull(c.precision, '') As varchar(3)) + ', ' + Cast(IsNull(c.scale, '') As varchar(10)) + ')'
                When Lower(type_name) In ('varbinary', 'binary') Then
                  + Case
                        When c.max_length = -1 Then
                            Cast(c.max_length As varchar(10))
                  + ')'
                When Lower(type_name) In ('char', 'varchar', 'nchar', 'nvarchar') Then
                  + Case
                        When c.max_length = -1 Then
                        When type_name In ('nchar', 'nvarchar') Then
                            Cast(c.max_length / 2 As varchar(10))
                            Cast(IsNull(c.max_length, '') As varchar(10))
                  + ')'
                  + Case
                        When c.collation_name != @database_collation Then
                            ' Collate ' + c.collation_name
                        Else ''
          + Case
                When c.is_nullable = 0 Then
                    ' not null'
                    ' null'
From        #temp c
Order By    column_id

Insert      @output_sql (sql)
Select      ');'

Select      sql
From        @output_sql
Order By    line_id

T-SQL Strip Invalid Characters

Occasionally I need to strip invalid characters from a string and the requirements are often subtly different, sometimes we want numbers only, other times numbers and decimal points, and maybe only letters.

We’ve probably all had to do this at some point and probably grabbed something off the internet, but I finally took the time to write a more generic and performant version as listed below which allows for a valid character pattern to be passed in.

Create Function dbo.StripInvalidCharacters
    Strips invalid characters from a string. This is useful for cleaning up
    strings such as telephone numbers or human entered values such as
    '10.7 miles'
        The string to strip characters from.
        A search pattern that identifies invalid characters. Some example are:
        - '0-9'    - numbers excluding decimal point
        - '0-9.'   - numbers including decimal point
        - 'a-z'    - letters only
        - 'a-f0-9' - hexadecimal only
    10-May-2016 S.Wilber
    @input varchar(1000)
   ,@valid_character_pattern varchar(100)
Returns varchar(1000)
    While PatIndex('%[^' + @valid_character_pattern + ']%', @input) > 0
        Set @input = Stuff(@input,PatIndex('%[^' + @valid_character_pattern + ']%', @input), 1, '')     

    -- return
    Return @input

Feel free to copy and re-use. If you spot any improvements, please let me know and I’ll update this post.

Clear All Tables Within a Schema

August 11, 2015 Leave a comment

Often as part of an ETL process I want to simply clear out all the table within a schema, e.g. ‘landing’ or ‘etl’.

However, as new tables are added to the schema, the ‘clear out’ code needs to be maintained. In addition, if any referential integrity exists, the tables will need to be cleared in a certain order. Finally, the Truncate Table statement is significantly faster than a simple Delete, but there are restrictions on when it can be used.
All of which led me to create the following stored procedure so that I don’t have to think these concerns again, allowing me time to focus on the core of the ETL work.

Feel free to use/copy/amend as appropriate, but please let me have your comments/updates.

Create Procedure etl.ClearSchemaTables
    Clears down any tables in the target schema.
    Tables are cleared down in referential order using truncate where possible.
        The name of the schema whose tables should be cleared, e.g. 'landing'.
    03-Aug-2015 S.Wilber
    @target_schema_name sysname

Set         NoCount On

-- declare variables
Declare     @object_id int
           ,@table_name sysname
           ,@schema_name sysname
           ,@is_referenced bit
           ,@success bit
           ,@sql nvarchar(max)

If Object_ID('tempdb..#table_dependencies') Is Not Null Drop Table #table_dependencies
Create Table #table_dependencies
    source_object_id int
   ,dependancy_object_id int

-- declare tables
If Object_ID('tempdb..#tables') Is Not Null Drop Table #tables
Create Table #tables
    object_id int
   ,schema_name sysname
   ,table_name sysname
   ,is_referenced bit default(0)
   ,is_processed bit default(0)

-- find all tables in the schema - look for fk references that are not from self
Insert      #tables (object_id, schema_name, table_name, is_referenced)
Select      t.object_id
           ,Case When fk.object_id Is Not Null Then 1 Else 0 End
From        sys.tables t
Inner Join  sys.schemas s On (s.schema_id = t.schema_id)
Left Join   sys.foreign_keys fk On (fk.referenced_object_id = t.object_id and fk.parent_object_id != t.object_id)
Where = @target_schema_name

-- retrieve all interdependancies between batch managed tables.
Insert      #table_dependencies (source_object_id, dependancy_object_id)
Select      fk.parent_object_id
From        sys.foreign_keys fk
Inner Join  #tables s On (s.object_id = fk.parent_object_id)
Inner Join  #tables t On (t.object_id = fk.referenced_object_id)

-- loop through all the tables delete the content, either via a truncate or delete depending on foreign keys
While Exists (Select 1 From #tables Where is_processed = 0)
    -- find the first table where all of the dependant tables have been processed
    Select      @object_id = object_id
               ,@schema_name = schema_name
               ,@table_name = table_name
               ,@is_referenced = is_referenced
    From        #tables sbt
    Where       is_processed = 0
    And         Not Exists
                    Select      1
                    From        #table_dependencies td
                    Inner Join  #tables tbt On (tbt.object_id = td.source_object_id)
                    Where       td.dependancy_object_id = sbt.object_id
                    And         tbt.is_processed = 0

    -- if none found, then raise an error as it seems that we have a circular dependancy that we can't resolve
    If @object_id Is Null
        RaisError ('A table where all dependant tables have been processed cannot be found. This implies that circular dependencies exist. Batch rollback cannot continue.', 11, 0)

    Begin Try
        -- if referenced then we need to perform a delete otherwise we can perform a truncate
        If @is_referenced = 1 
            Set         @sql = 'Delete From [' + @schema_name + '].[' + @table_name + ']'
            Set         @sql = 'Truncate Table [' + @schema_name + '].[' + @table_name + ']'
        -- exeute the sql
        Exec        sp_executesql @stmt = @sql          
    End Try
    Begin Catch
        -- flag as unsuccessful
        Set         @success = 0

        -- declare variables
        Declare         @error_description varchar(2000)
                       ,@error_severity int
                       ,@error_state int

        -- fetch the error details
        Select         @error_description = ERROR_MESSAGE(), @error_severity = ERROR_SEVERITY(), @error_state = ERROR_STATE()

        -- throw the error
        RaisError (@error_description, @error_severity, @error_state) 
    End Catch
    -- update the table to state that that it has been processed
    Update      #tables
    Set         is_processed = 1
    Where       object_id = @object_id

Temporarily Disabling Referential Integrity Constraints on a SQL Table

I recently came across a situation where part of the data processing would put the data temporarily into a non-referential state. In order to accommodate this, without scripting Drop/Create statements which could get out of sync with other development work, I put together the following stored procedure which enables/disables check constraints.

Feel free to use/copy/amend as appropriate, but please let me have your comments/updates.

Create Procedure [etl].[SetCheckContraintsState]
    Enables/Disables any check contraints that reference the target table.
    This is useful for when referenced data is going to be temporarily modified
    in a way that will invalidate any check constraints.
    02-Jun-2015 S.Wilber
    @target_schema_name sysname
   ,@target_table_name sysname
   ,@do_set_enabled bit

-- declare variables
Declare     @constraint_name sysname
           ,@referencing_schema_name sysname
           ,@referencing_table_name sysname
           ,@sql nvarchar(max)

Declare @constraints table
    ConstraintName sysname
   ,ReferencingSchemaName sysname
   ,ReferencingTableName sysname

Insert      @constraints (ConstraintName, ReferencingSchemaName, ReferencingTableName)
Select As ConstraintName
           , As ReferencingSchemaName
           , As ReferencingTableName
From        sys.foreign_keys fk
Inner Join  sys.tables t On (t.object_id = fk.parent_object_id)
Inner Join  sys.schemas sch On (sch.schema_id = t.schema_id)
Where       fk.referenced_object_id = Object_ID(QuoteName(@target_schema_name) + '.' + QuoteName(@target_table_name))

Declare     constraint_cursor Cursor Fast_Forward For
Select      ConstraintName
From        @constraints

Open constraint_cursor
Fetch From constraint_cursor Into @constraint_name, @referencing_schema_name, @referencing_table_name

While @@Fetch_Status = 0
    If @do_set_enabled = 1
        Set @sql = 'Alter Table ' + QuoteName(@referencing_schema_name) + '.' + QuoteName(@referencing_table_name) + ' With Check Check Constraint ' + QuoteName(@constraint_name)
        Set @sql = 'Alter Table ' + QuoteName(@referencing_schema_name) + '.' + QuoteName(@referencing_table_name) + ' NoCheck Constraint ' + QuoteName(@constraint_name)

    Exec sp_executesql @sql

    -- get the next constraint
    Fetch From constraint_cursor Into @constraint_name, @referencing_schema_name, @referencing_table_name

Close constraint_cursor
Deallocate constraint_cursor

Mark Items as Default in Reference Data … and Ensure There is Only One

November 6, 2013 Leave a comment


Often it is convenient to be able to default values in where they are not specified, or to not require items to be specified to make life easier.
For maintainability it is best to mark default values in the data itself, rather than in some code somewhere, and where better than in the source reference table.
By adding a bit column ‘IsDefault’ it is simple to mark a particular record as the default, however it is also easy to mark several items as default by mistake.
But with careful use of a filtered unique index it is possible to apply a constraint such that there can be only one default record as below.


Create Unique NonClustered Index IX_UNIQUE_IS_DEFAULT On MyReferenceTable
	IsDefault Asc
Where (IsDefault=(1))


By filtering, we don’t index the ‘false’ values so that more than one record can be marked as “not the default”, and by making it unique we ensure that we only have a single record marked as default.