sql server 返回计算表达式的函数

下面为您介绍一个SQL中返回计算表达式的函数，该函数可以计算加、减、乘、除，但是不能算幂，供您参考，希望对您学习SQL中的函数能有有所帮助。

CREATE FUNCTION [dbo].[GetExp](@pstrExpress AS VARCHAR(8000))
RETURNS DECIMAL(18,6) AS
BEGIN
DECLARE @i INT,@j INT 
DECLARE @c1 CHAR(1),@c2 CHAR(1),@c VARCHAR(100)
DECLARE @v1 DECIMAL(18,6),@v2 DECIMAL(18,6),@v DECIMAL(18,6)
DECLARE @t TABLE(ID INT IDENTITY(1,1),s VARCHAR(100))
DECLARE @s TABLE(ID INT IDENTITY(1,1),s VARCHAR(100))
DECLARE @sv TABLE(ID INT IDENTITY(1,1),v DECIMAL(18,6))

SET @pstrExpress = REPLACE(@pstrExpress,' ','')
SELECT @i = 0,@j = LEN(@pstrExpress),@c2 = '',@c = ''
WHILE @i<@j
BEGIN
 SELECT @c1 = @c2,@i = @i+1
 SELECT @c2 = SUBSTRING(@pstrExpress,@i,1)
 IF CHARINDEX(@c2,'.0123456789') > 0 or (@c2 = '-' and @c1 IN('','*','-','+','/','('))
 BEGIN   SELECT @c = @c + @c2   CONTINUE  END
 IF @c <> ''  BEGIN INSERT @t(s)  SELECT @c SELECT @c = '' END
 IF CHARINDEX(@c2,')')>0
 BEGIN 
   INSERT @t(s)  SELECT s FROM @s WHERE ID > ISNULL((SELECT MAX(ID) FROM @s WHERE s IN('(')),0) ORDER BY ID DESC
   DELETE @s WHERE ID >= ISNULL((SELECT MAX(ID) FROM @s WHERE s IN('(')),0) 
   CONTINUE
 END
 IF CHARINDEX(@c2,'+-)')>0
 BEGIN 
   INSERT @t(s)  SELECT s FROM @s WHERE ID > ISNULL((SELECT MAX(ID) FROM @s WHERE s IN('(')),0) ORDER BY ID DESC
   DELETE @s WHERE ID > ISNULL((SELECT MAX(ID) FROM @s WHERE s IN('(')),0) 
   IF @c2 <> ')' INSERT @s(s) SELECT @c2
   CONTINUE
 END
 IF CHARINDEX(@c2,'*/')>0
 BEGIN 
   INSERT @t(s)  SELECT s FROM @s WHERE ID > ISNULL((SELECT MAX(ID) FROM @s WHERE s IN('(','+','-')),0) ORDER BY ID DESC
   DELETE @s WHERE ID > ISNULL((SELECT MAX(ID) FROM @s WHERE s IN('(','+','-')),0) 
   INSERT  @s SELECT @c2
   CONTINUE
 END
 IF CHARINDEX(@c2,'(')>0 INSERT  @s SELECT @c2
END
IF @c <> '' INSERT @t(s) SELECT @c
INSERT @t(s)  SELECT s FROM @s ORDER BY ID DESC
SELECT @i = 0,@j = MAX(ID) FROM @t 
WHILE @i < @j
BEGIN 
 SELECT @i = @i + 1
 SELECT @c = s FROM @t WHERE ID = @i
 IF @c = '(' CONTINUE
 IF @c NOT IN('*','-','+','/')  BEGIN  INSERT @sv(v) SELECT CONVERT(float,@c) CONTINUE END
 SELECT @v2 = v FROM @sv  DELETE @sv  WHERE ID = (SELECT MAX(ID) FROM @sv)
 SELECT @v1 = v FROM @sv  DELETE @sv  WHERE ID = (SELECT MAX(ID) FROM @sv)
 SELECT @v = CASE @c WHEN '+' THEN @v1 + @v2 WHEN '-' THEN @v1 - @v2
                     WHEN '*' THEN @v1 * @v2 WHEN '/' THEN @v1 / @v2 END
 INSERT @sv(v) SELECT @v
END
SELECT @v = v FROM @sv
RETURN @v
END