Tuesday, 25 July 2017

MSSQL - How to clear all caches?

Script to clear all caches? (For example for performance debug)

/*
https://yabele.blogspot.com/2017/07/mssql-how-to-clear-all-caches.html
*/
SET NOCOUNT ON;
GO
CHECKPOINT; 
GO
DBCC DROPCLEANBUFFERS;
DBCC FREESYSTEMCACHE ('ALL');
GO
DECLARE @StartedAt DATETIME2 = GETDATE();
-- Query
PRINT '    Elapsed time: ' + CAST(DATEDIFF(ms, @StartedAt, GETDATE()) AS VarChar(20)) + ' ms';

MSSQL - T-SQL equivalent of VBA VAL() function

There the text of scalar-value function to extract numbers from string and convert to integer:

IF OBJECT_ID(N'dbo.fn_extract_digits') IS NOT NULL
  DROP FUNCTION dbo.fn_extract_digits;
GO

CREATE FUNCTION dbo.fn_extract_digits (@str VARCHAR(MAX))
/*
https://yabele.blogspot.com/2017/07/mssql-t-sql-equivalent-of-vba-val.html
*/
RETURNS INT
AS
BEGIN
  DECLARE
    @newstr VARCHAR(MAX) = '',
    @i INT = 1,
    @chr CHAR(1);

  WHILE @i <= LEN(@str) BEGIN
    SET @chr = SUBSTRING(@str, @i, 1);
    IF @chr BETWEEN '0' AND '9'
      SET @newstr = @newstr + @chr;
    SET @i = @i + 1;
  END;

  RETURN CAST(@newstr AS INT);
END
/*
DECLARE @str VARCHAR(MAX) = '1-23-456';
SELECT Digits = dbo.fn_extract_digits(@str);*/
;

MSSQL - Function to generate empty rows

There the text of inline table-value function to generate a specified count of empty rows:

IF OBJECT_ID(N'dbo.GenerateRows') IS NOT NULL
  DROP FUNCTION dbo.GenerateRows;
GO
CREATE FUNCTION dbo.GenerateRows (@Count INT)
/*
https://yabele.blogspot.com/2017/07/mssql-function-to-generate-empty-rows.html
*/
RETURNS TABLE
AS
RETURN
WITH TenRows AS (
  SELECT * FROM (VALUES (1),(2),(3),(4),(5),(6),(7),(8),(9),(10)) AS T(I)
)
SELECT TOP(@Count)
  I = ROW_NUMBER() OVER(ORDER BY (SELECT 1))
FROM
  TenRows T1 CROSS JOIN TenRows T2 CROSS JOIN TenRows T3 CROSS JOIN TenRows T4 CROSS JOIN TenRows T5
/*
SELECT * FROM dbo.GenerateRows(100);
*/
;

Wednesday, 24 August 2016

MSSQL - How to generate range of Dates

There the text of VIEW to generate range of dates between 1.January 2000 and 31.December next year:

IF OBJECT_ID(N'dbo.calendar_dates') IS NOT NULL
  DROP VIEW  dbo.calendar_dates;
GO
/*
http://yabele.blogspot.de/2016/08/how-to-generate-range-of-dates.html
*/
CREATE VIEW dbo.calendar_dates
AS
WITH
  R10 AS (
    SELECT * FROM (VALUES (1),(2),(3),(4),(5),(6),(7),(8),(9),(10)) AS T(I)
  )
SELECT TOP(DATEDIFF(DAY, '2000-01-01', CAST(YEAR(GETDATE()) + 1 AS CHAR(4)) + '-12-31'))
  date_value = DATEADD(DAY, ROW_NUMBER() OVER(ORDER BY (SELECT 1)), '1999-12-31')
FROM
  R10 T1 CROSS JOIN R10 T2 CROSS JOIN R10 T3 CROSS JOIN R10 T4 CROSS JOIN R10 T5 CROSS JOIN R10 T6
/*
SELECT *
FROM dbo.calendar_dates
ORDER BY date_value;
*/
;

Monday, 17 August 2015

MSSQL - How to replicate to readonly database?

First, I have to apologize, title of article lies - it is unfortunately impossible to set up replication into the READ-ONLY database.
One of the reasons why we want to have the target database read-only, is the need to avoid direct changes of data in it.
For this purpose, we can use another method - Triggers, which prohibit any changes except changes from the replication.

There such trigger:
USE MySourceDB
GO
ALTER TRIGGER dbo.trig_mytable_CheckContext4Changes ON dbo.MyTable
    FOR INSERT, UPDATE, DELETE
    NOT FOR REPLICATION
AS
IF NOT (@@SERVERNAME = 'MySourceServer' AND DB_NAME = 'MySourceDB')
    ROLLBACK;

Very important is this expression: NOT FOR REPLICATION.
On the target database at the same time we have to
- prohibit all direct changes (INSERT/UPDATE/DELETE)
- but allow data changes which are comming from replication
Expression NOT FOR REPLICATION deactivates trigger for changes from replication.

Monday, 10 August 2015

MSSQL - Immediately PRINT big messages - more then 8000 bytes (4000 unicode characters)

Transact-SQL function PRINT has two disadvatages:
- is limited for 8000 bytes - 8000 VARCHAR characters or 4000 NVARCHAR (unicode) characters
- does not send messages immediately to the client, usually user have to wait until the procedure is complete before seeing messages

We can use alternate method - the RAISERROR function, this function can send messages immediately, but is limited for 2047 characters.

There the stored procedure which send any messages immediately to client, also with length more then 2047 (or 8000) characters:
CREATE PROCEDURE [dbo].[sp_print_big_message]
    @message NVARCHAR(MAX)
AS BEGIN

    -- SET NOCOUNT ON to prevent extra log messages
    SET NOCOUNT ON;

    DECLARE
        @CRLF            CHAR(2) = CHAR(13)+CHAR(10),
        @message_len    INT = LEN(@message),
        @i                INT,
        @part            NVARCHAR(2000),
        @part_len        INT;

    IF @message_len <= 2000 BEGIN
        -- Message ist enough short
        RAISERROR (@message, 0,1) WITH NOWAIT;
    END ELSE BEGIN
        -- Message is too long
        SET @i = 1;
        WHILE @i < LEN(@message) BEGIN
            -- Split to parts end send them to client immediately
            SET @part = SUBSTRING(@message, @i, 2000);
            SET @part_len = 2000 - CHARINDEX(CHAR(10) + CHAR(13), REVERSE(@part)) - 1;
            SET @part = CASE @i
                            WHEN 1
                            THEN ''
                            ELSE '/* CRLF ' + CAST(@i AS VARCHAR(20)) + ':'
                                 + CAST(@part_len AS VARCHAR(20)) + ' */' + @CRLF
                        END
                        + REPLACE(SUBSTRING(@message, @i, @part_len), '%', '%%');
            RAISERROR (@part, 0,1) WITH NOWAIT;
            SET @i = @i + @part_len + 2;
        END;
    END;

END;

Usage:
-- Declare long message
DECLARE @LongMessage NVARCHAR(MAX) = '';
-- Fill message with test data
DECLARE @i INT = 1;
WHILE @i < 200 BEGIN
    SET @LongMessage = @LongMessage
                       + CASE @i WHEN 1 THEN '' ELSE CHAR(13) + CHAR(10) END
                       + CAST(@i AS VARCHAR(10))
                       + '. Lorem ipsum dolor sit amet, consectetur adipiscing elit.';
    SET @i = @i + 1;
END;

-- Display length of generated message
DECLARE @len INT = LEN(@LongMessage);
RAISERROR('Message length: %i', 0, 1, @len);

-- Use SP to print long message
EXEC sp_print_big_message @LongMessage;

Monday, 3 August 2015

MSSQL - Convert speсial types to strings or HTML:
  • MONEY to string,
  • DATETIME to string,
  • GUID or UNIQUEIDENTIFIER to string,
  • VARBINARY or BINARY to string,
  • XML to string,
  • TIMESTAMP to string

Most of datatypes is relative simple convert to a string.
For this we can use the CONVERT() or even the CAST() function:
SELECT int_as_string = CONVERT(VARCHAR(20), int_field) FROM MyTable;

SELECT int_as_string = CAST(int_field AS VARCHAR(20))  FROM MyTable;

But for some other datatypes convert is not so simple.
For example for MONEY, DATETIME, UNIQUEIDENTIFIER, BINARY, XML and TIMESTAMP datatypes.

There the script which shows how to convert such datatypes to strings:
USE tempdb;
GO

-- Drop test table if exists
IF OBJECT_ID('test_converts') IS NOT NULL
    DROP TABLE test_converts;
GO

-- Create test table
-- The technique to generate random money value I have used from there:
--     http://yabele.blogspot.de/2013/08/mssql-random-number-generator-with.html
CREATE TABLE test_converts
(
    mon MONEY             NOT NULL DEFAULT RAND(CHECKSUM(NEWID())) * 1000,
    dt DATETIME           NOT NULL DEFAULT GETDATE(),
    guid UNIQUEIDENTIFIER NOT NULL DEFAULT NEWID(),
    bin VARBINARY(MAX)    NOT NULL DEFAULT NEWID(),
    x XML                 NOT NULL,
    ts TIMESTAMP
);
GO

-- Fill test table with 3 records
-- For all columns except "x" (xml) the default values will be used
INSERT INTO test_converts (x)
VALUES
    ('<a b="c"><d/></a>'),
    ('<e f="g"><h/></e>'),
    ('<i j="k"><l/></i>');

-- Show original values
SELECT * FROM test_converts;

-- Convert values to string
SELECT
                          -- Third parameter (0) is default and generates result text
                          -- in "0.00" format
    money_as_string     = CONVERT(VARCHAR(20), mon, 0),
                          -- Third parameter (121) generates result text
                          -- in ODBC-canonical format: "yyyy-MM-dd HH:mm:ss.sss"
    datetime_as_string  = CONVERT(VARCHAR(30), dt, 121),
    guid_as_string      = CONVERT(VARCHAR(36), guid),
                          -- Third parameter (1) generates result text
                          -- in uppercase form with "0x" prefix
    binary_as_string    = CONVERT(VARCHAR(MAX), bin, 1),
    xml_as_string       = CONVERT(VARCHAR(MAX), x),
    timestamp_as_string = CONVERT(VARCHAR(MAX), CONVERT(VARBINARY(MAX), ts), 1)
FROM
    test_converts;

After execution in SSMS (SQL Server Management Studio) we will have these two resultsets:



These techniques could be used for example to convert table-content to HTML.
In case you need convert values to HTML-string some converted string values will be necessary to HTML-encode:
-- Convert values to HTML-string
SELECT
                        -- Third parameter (0) is default and generates result text
                        -- in "0.00" format
    money_as_HTML     = CONVERT(VARCHAR(20), mon, 0),
                        -- Third parameter (121) generates result text
                        -- in ODBC-canonical format: "yyyy-MM-dd HH:mm:ss.sss"
    datetime_as_HTML  = CONVERT(VARCHAR(30), dt, 121),
    guid_as_HTML      = CONVERT(VARCHAR(36), guid),
                        -- Third parameter (1) generates result text
                        -- in uppercase form with "0x" prefix
    binary_as_HTML    = CONVERT(VARCHAR(MAX), bin, 1),
                        -- Convert XML-string to HTML-encoded string
    xml_as_HTML       = REPLACE(REPLACE(REPLACE(
                            CONVERT(VARCHAR(MAX), x)
                        , '&','&amp;'), '<', '&lt;'), '>', '&gt;'),
    timestamp_as_HTML = CONVERT(VARCHAR(MAX), CONVERT(VARBINARY(MAX), ts), 1)
FROM
    test_converts;

Correspondent resultset in SSMS:



See also:
MSSQL - The random number generator with a random initialization (random seed)