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Monday 11 March 2013

SQL Server – Generating PERMUTATIONS using T-Sql

Were you ever asked to generate string Permutations using TSql? I was recently asked to do so, and the logic which I could manage to come up at that point is shared in the below script.

DECLARE @Value AS VARCHAR(20) = 'ABCC' --Mention the text which is to be permuted
DECLARE @NoOfChars AS INT = LEN(@Value)
DECLARE @Permutations TABLE(Value VARCHAR(20)) --Make sure the size of this Value is equal to your input  string length (@Value)
 
;WITH NumTally AS (--Prepare the Tally Table to separate each character of the Value.
  SELECT 1 Num
  UNION ALL
  SELECT 
    Num + 1 
  FROM 
    NumTally 
  WHERE 
    Num < @NoOfChars
),Chars AS ( --Separate the Characters
SELECT
  Num,
  SUBSTRING(@Value,Num,1) Chr
FROM
  NumTally  
)
 
--Persist the Separated characters.
INSERT INTO @Permutations
SELECT Chr FROM Chars
 
--Prepare Permutations
DECLARE @i AS INT = 1
WHILE(@i < @NoOfChars)
BEGIN
 
  --Store the Permutations
  INSERT INTO @Permutations
  SELECT DISTINCT --Add DISTINCT if required else duplicate Permutations will be generated for Repeated  Chars.
    P1.Value + P2.Value
  FROM 
    (SELECT Value FROM @Permutations WHERE LEN(Value) = @i) P1 
  CROSS JOIN 
    (SELECT Value FROM @Permutations WHERE LEN(Value) = 1) P2
  
  --Increment the Counter.      
  SET @i += 1  
  
  --Delete the Incorrect Lengthed Permutations to keep the table size under control.
  DELETE FROM @Permutations WHERE LEN(Value) NOT IN (1,@i)
END
 
--Delete InCorrect Permutations.
SET @i = 1
WHILE(@i <= @NoOfChars)
BEGIN
 
  --Deleting Permutations which has not used "All the Chars of the given Value".
  DELETE 
  FROM 
    @Permutations
  WHERE
    Value NOT LIKE '%' + SUBSTRING(@Value,@i,1) +'%'
  
  --Deleting Permutations which have repeated incorrect character.  
  DELETE 
  FROM 
    @Permutations
  WHERE
    LEN(Value) - LEN(REPLACE(Value,SUBSTRING(@Value,@i,1),'')) != 
    LEN(@Value) - LEN(REPLACE(@Value,SUBSTRING(@Value,@i,1),''))
    
  SET @i += 1  
END
 
--Selecting the generated Permutations. 
SELECT Value FROM @Permutations

Hope, this script helps!


Please share your suggestions if you have any to improve this logic.

Wednesday 6 March 2013

SQL Server – TSql to find Records matching certain criteria in all the tables of a DB.

Generally, we try to find out records matching a certain criteria from a single or few tables. However, there are times when we need to find out records matching a criteria from all the tables of a SQL Database and today I will explain you a simple way to retrieve those records.

Recently, I was asked by my colleague, who was working on a MS Dynamics CRM migration project, to let him know the records which were created after a particular date in the source. So that, he could analyze only those records and strategize the Migration process.

I quickly opened up the SSMS and came up with the below script -

USE <DBName> --Replace this with the actual DBName
Go
 
DECLARE @ColumnName AS VARCHAR(50) = 'CreatedOn' --The name of the column on which you need to put the criteria
DECLARE @Criteria AS VARCHAR(50) = 'CONVERT(DATE,' + @ColumnName + ') >= ''20130225''' -- The Actual criteria/WHERE Clause of the query
 
--The below will list the TSQL Statements which could be copied & executed in a separate query window.
SELECT 
  'IF EXISTS(SELECT 1 FROM ' + T.name + ' WHERE ' + @Criteria + ') ' +
  'SELECT ''' + T.name + ''' TableName, * FROM ' + T.name + ' WHERE ' + @Criteria 
FROM 
  sys.columns C
INNER JOIN sys.tables T
  ON T.object_id = C.object_id   
WHERE 
  C.name = @ColumnName


The above script will list down the SELECT statements which could be copied and executed in a separate query window connecting to the same Database. On execution, you will get the list of records from each table base on the specified criteria.


Hope, this helps!