Keywords ALL/SOME/ANY

Compares a scalar value with a single-column set of values. SOME and ANY are equivalent.

Here is the example:

CREATE TABLE T1
(ID int) ;
GO
INSERT T1 VALUES (1) ;
INSERT T1 VALUES (2) ;
INSERT T1 VALUES (3) ;
INSERT T1 VALUES (4) ;

it will return "TRUE", because 3 less than some vaules in table.

IF 3 < SOME (SELECT ID FROM T1)
PRINT 'TRUE' 
ELSE
PRINT 'FALSE' ;

it will return "FALSE", because 3 no less than all vaules in table.

IF 3 < ALL (SELECT ID FROM T1)
PRINT 'TRUE' 
ELSE
PRINT 'FALSE' ;

 in some statements

CREATE TABLE #M1(C1 INT)
INSERT #M1
SELECT 2 UNION 
SELECT 3 UNION 
SELECT 4  

CREATE TABLE #M2(C1 INT)
INSERT #M2
SELECT 1 UNION 
SELECT 2 UNION 
SELECT 5 
--意思是 #M1.C1里面的哪些值不等于 #M2.C1全部值里面的一些值，有点绕，比如：#M1.C1里面的 2 不等于 #M2.C1 全部值里面的一些值（比如不等于1和5），所以2会被查询出来
SELECT * FROM #M1 WHERE C1 <> SOME(SELECT C1 FROM #M2)
SELECT * FROM #M1 WHERE C1 = SOME(SELECT C1 FROM #M2)
--下面只有2是不等于#M2里面所有值的,其实这里的 "<> all" = "not in"

SELECT * FROM #M1 WHERE C1 <> all(SELECT C1 FROM #M2)
--同理，下面是空
SELECT * FROM #M1 WHERE C1 = all(SELECT C1 FROM #M2)