SELECT (CASE 'Chaine1' WHEN 'Chaine1' THEN 1 ELSE 0 END) as CHAINE;
SELECT (CASE 'Chaine1' WHEN ' Chaine1' THEN 1 ELSE 0 END) as CHAINE;
SELECT (CASE 'Chaine1' WHEN 'Chaine1 ' THEN 1 ELSE 0 END) as CHAINE;

SELECT (CASE '' WHEN '' THEN 1 ELSE 0 END) as RESULT;
SELECT (CASE '' WHEN ' ' THEN 1 ELSE 0 END) as RESULT;
SELECT (CASE ' ' WHEN '' THEN 1 ELSE 0 END) as RESULT;

SELECT LEN(fieldname) FROM table;

CREATE TABLE TEST (
	[id] [int] NOT NULL ,
	[text] [nvarchar] (50) NOT NULL 
) ON [PRIMARY]
GO

ALTER TABLE [TEST] WITH NOCHECK ADD 
	CONSTRAINT [PK_TEST] PRIMARY KEY  CLUSTERED 
	(
		[id]
	)  ON [PRIMARY] 
GO

CREATE  UNIQUE  INDEX [IX_TEST] ON [TEST]([text]) ON [PRIMARY]
GO

/* Insert with a trailing space *:
INSERT INTO TEST (id, text)
VALUES     (1, 'a ')
GO
INSERT INTO TEST (id, text)
VALUES     (1, 'b')
GO
/* Then SELECT with like */
SELECT     *
FROM         TEST
WHERE     text LIKE 'a'
 /* Returns nothing */
SELECT     *
FROM         TEST
WHERE     text LIKE 'a '
/* Returns 1, 'a ' */
SELECT     *
FROM         TEST
WHERE     text LIKE '_ '
/* Returns 1, 'a ' */
SELECT     *
FROM         TEST
WHERE     text LIKE '% '
/* returns 1,'a ' */
GO

SELECT LEN(fieldname) FROM table;

CREATE TABLE TEST (
	[id] [int] NOT NULL ,
	[text] [nvarchar] (50) NOT NULL 
) ON [PRIMARY]
GO

ALTER TABLE [TEST] WITH NOCHECK ADD 
	CONSTRAINT [PK_TEST] PRIMARY KEY  CLUSTERED 
	(
		[id]
	)  ON [PRIMARY] 
GO

CREATE  UNIQUE  INDEX [IX_TEST] ON [TEST]([text]) ON [PRIMARY]
GO

/* Insert with a trailing space *:
INSERT INTO TEST (id, text)
VALUES     (1, 'a ')
GO
INSERT INTO TEST (id, text)
VALUES     (1, 'b')
GO
/* Then SELECT with like */
SELECT     *
FROM         TEST
WHERE     text LIKE 'a'
 /* Returns nothing */
SELECT     *
FROM         TEST
WHERE     text LIKE 'a '
/* Returns 1, 'a ' */
SELECT     *
FROM         TEST
WHERE     text LIKE '_ '
/* Returns 1, 'a ' */
SELECT     *
FROM         TEST
WHERE     text LIKE '% '
/* returns 1,'a ' */
GO

len('a')
len('a ')
len('a         ')

len(' a')
is 2.