SQL 8115 Arithmetic overflow error converting numeric to data type numeric

Question

I obtain on my SQL Server 2005 an error

Server: Msg 8115, 
Arithmetic overflow error converting numeric to data type numeric.

When I try to insert a value = X(DECIMAL(3,2)) * Y(INT)
in a column MYCOLUMN typed DECIMAL (10,3)

How to workaround this problem?

UPDATE

some code bellow to understand the situation

-- ============================================================
--   Table : GP_WGENTH
-- ============================================================
CREATE TABLE #GP_WGENTH
(
     KEYINTERNAL                     CHAR(32)              NOT NULL,
     KEYHOUR                         INT                   NOT NULL,
     FIRM                            CHAR(5)               NOT NULL,
     CENTRE                          CHAR(2)               NOT NULL,
     SERVICE                         CHAR(6)               NOT NULL,
     AGENT                           CHAR(5)               NOT NULL,
     VERSION                         VARCHAR(3)            NOT NULL,
     DATE_ROULEMENT                  DATETIME              NOT NULL,
     SERVICEINSTANCE                 SMALLINT              NOT NULL,
     TYPEHOUR                        CHAR(9)               NOT NULL,
     QUANTITEFIXE                    DECIMAL(12,2)         NULL    ,
     TYPECMP                         INT                   NULL    ,
     PERCENTCALC                     DECIMAL(3,2)          NULL    
)
-- ============================================================
--   Table : GP_WGENSVCTH
-- ============================================================
CREATE TABLE #GP_WGENSVCTH
(
    KEYINTERNAL                     CHAR(32)              NOT NULL,
    KEYHOUR                         INT                   NOT NULL,
    FIRM                            CHAR(5)               NOT NULL,
    CENTRE                          CHAR(2)               NOT NULL,
    SERVICE                         CHAR(6)               NOT NULL,
    AGENT                           CHAR(5)               NOT NULL,
    VERSION                         VARCHAR(3)            NOT NULL,
    DATE_ROULEMENT                  DATETIME              NOT NULL,
    SERVICEINSTANCE                 SMALLINT              NOT NULL,
    TYPEHOUR                        CHAR(9)               NOT NULL,
    VALUE                           DECIMAL(10,3)         NOT NULL
)
GO

INSERT INTO #GP_WGENSVCTH 
            (KEYINTERNAL, 
             KEYHOUR, 
             FIRM, 
             CENTRE, 
             SERVICE, 
             AGENT, 
             VERSION, 
             DATE_ROULEMENT, 
             SERVICEINSTANCE, 
             TYPEHOUR, 
             VALUE) 
SELECT WTH.KEYINTERNAL, 
       WTH.KEYHOUR, 
       WTH.FIRM, 
       WTH.CENTRE, 
       WTH.SERVICE, 
       WTH.AGENT, 
       WTH.VERSION, 
       WTH.DATE_ROULEMENT, 
       WTH.SERVICEINSTANCE, 
       WTH.TYPEHOUR, 
       WTH.PERCENTCALC * SUM(SC.LENGTH) -- !!! BOOOM !!!!!!!!! HERE
FROM   #GP_WGENTH WTH 
       INNER JOIN GP_SERVICE_HABILLAGE_COMPONENT SC 
               ON WTH.FIRM = SC.FIRM 
                  AND WTH.CENTRE = SC.CENTRE 
                  AND WTH.SERVICE = SC.SERVICE 
                  AND WTH.VERSION = SC.VERSION 
                  AND WTH.TYPECMP = SC.TYPECMP 
WHERE  WTH.KEYINTERNAL = 'august 23 2012  10:45:21:027PM     ' 
       AND SC.LENGTH IS NOT NULL 
GROUP  BY WTH.KEYINTERNAL, 
          WTH.KEYHOUR, 
          WTH.FIRM, 
          WTH.CENTRE, 
          WTH.SERVICE, 
          WTH.AGENT, 
          WTH.VERSION, 
          WTH.DATE_ROULEMENT, 
          WTH.SERVICEINSTANCE, 
          WTH.TYPEHOUR, 
          WTH.PERCENTCALC 

Answer 1

The rules for the necessary scale, precision and length are well covered in MSDN documentation.

Decimal is just a scaled integer, so let's look at an example with no decimal point.

For example X DECIMAL(3, 0) and Y DECIMAL(3, 0) where X = 100 and Y = 100, X * Y = 10000 which will not fit in DECIMAL(3, 0), and requires DECIMAL(5, 0). In fact, 999 * 999 = 998001 which would require DECIMAL(6, 0).

So trying to insert the result of multiplying two decimal columns will only fit if the destination column has a capacity at least as great as that indicated by the formulas in the MSDN table for the different operations.