Mamta Satoor wrote:
Dan, I looked at the SQL 2002 foundation specification.
TRIM, UPPER, LOWER, SUBSTRING functions are covered in Section 6.29
<string value function> and it says that these functions will get the
collation of their operand. For instance, Syntax Rule (4b) says this
for SUBSTRING function "The character set and collation of the
<character substring function> are those of DTCVE." DTCVE is the
declared type of the <character value expression>. Same thing is
implied for UPPER and LOWER functions (Syntax Rule 8), TRIM function
(Syntax Rule 11).
I am not too clear on what happens when CAST is used. SQL spec
discusses this in section 6.12 <cast specification> and says in Syntax
Rule 10) that "The declared type collation of the <cast specification>
is the character set collation of the character set of TD and its
collation derivation is implicit." So for the eg case CAST(charC1 as
VARCHAR(30)), what will be the collation of VARHCHAR(30) value? Is
Derby's character set's collation is UCS_BASIC? If so, then will the
CAST value (if casted to one of the character datatypes) always have
collation of UCS_BASIC no matter if charC1 has UCS_BASIC /
TERRITORY_BASED collation?
Hi Mamta,
You've probably seen this in section 6.1: as part of the CAST, you can
specify the collation you want. E.g.:
CAST englishColumn as VARCHAR(300) COLLATE germanCollation
Regards,
-Rick
As for concatenation, Section 9.3 Data types of results of
aggregations has Sytax Rules 2)All of the data types shall be
comparable. I take that to mean that
userChar1WithTerritoryBasedCollation can't be concatenated with
systemChar1 because systemChar1 has UCS_BASIC collation. But if the
datatypes are comparable, then the result of concatenation will have
the collation type of the operands.
I hope I covered it all. Looking forward to feedback,
Mamta
On 3/19/07, *Daniel John Debrunner* <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> wrote:
Mamta Satoor wrote:
> Hi Dan,
>
> You asked about how collation will be set for character
expressions like
> string literal, cast to character type of a character
expression, trim,
> concationation etc.
>
> DTD will have an attribute called collation type and in 10.3, the
> possible values for it will be -1 meaning UNKNOWN collation, 0
meaning
> UCS_BASIC and 1 meaning TERRITORY_BASED. By default, DTD's will
have the
> collation type set to UNKNOWN. If the DTD is for a user table's CHAR
> column, then DTD's collation will be set to
TERRIOTRY_BASED/UCS_BASIC
> depending on what was requested at database create time in the
jdbc url.
> This setting of collation will be done by
DTD.setCollationType(int). If
> the DTD is for a SYS schema table's CHAR column, then DTD's
collation
> will be set to UCS_BASIC.
>
> I think there is a DTD associated with all the character expressions
> like string literal, cast to character type of a character
expression,
> trim, concationation etc. And since the default collation type is
> UNKNOWN, these character expressions will have their collation
type as
> UNKNOWN until they actually get used in a collation method. When
they
> get used in a collation method, their collation type will be
determined
> by the context in which they are. ie if the other operand of the
> collation method has UCS_BASIC associated with them, then the
character
> expression's collation type in DTD will get set to UCS_BASIC and
similar
> logic if the other operand had TERRITORY_BASED collation type
associated
> with it.
>
> I hope this answers your question. I will include this
information on
> the wiki page for DERBY-1478 so that everything is tracked in one
> central location.
I'm not sure it's a simple as that. Consider this expression:
TRIM(x) < 'eee'
If x is a user column then I would expect the collation to be
performed
using the collation for user columns, but if x was a system column I
would expect it to be performed using UCS_BASIC. I think it would be
much like nullability, the nullability of some operation of x is
dependent on the nullability of x, hence the collation of some
operation
of x would be dependent on the collation of x.
Though of course, maybe the SQL standard defines it differently, it
would be good to know if it's defined by the standard or left as
implementation defined.
Dan.
