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http://issues.apache.org/jira/browse/DERBY-1306?page=comments#action_12449042 ]
Christian d'Heureuse commented on DERBY-1306:
---------------------------------------------
I found the following comment within
org.apache.derby.impl.sql.compile.ConcatenationOperatorNode:
/* If either the left or right operands are non-string, non-bit types,
* then we generate an implicit cast to VARCHAR.
*/
The concatenation operator probably worked in the documented way in a previous
Derby version.
The statement
VALUES CAST(123 AS VARCHAR(10));
Produces the same error:
Cannot convert types 'INTEGER' to 'VARCHAR'.
The statement
VALUES CAST(123 AS CHAR(10));
works (but produces trailing blanks).
This is correct according to the documentation of CAST (see also DERBY-1804).
But it's a bit strange that conversions from INTEGER to CHAR and even from
VARCHAR to INTEGER are allowed, but the conversion from INTEGER to VARCHAR is
not allowed.
I don't understand why the conversion from INTEGER to VARCHAR is not supported.
The class org.apache.derby.iapi.types.SQLVarchar inherits the setValue(int)
method from SQLChar and there is nothing special about it:
public void setValue(int theValue) throws StandardException
{
setValue(Integer.toString(theValue));
}
Even DATE and TIME values can be converted to VARCHAR, so why not INTEGER?
Another issue:
Why does the JavaDoc of the ConcatenationOperatorNode class say: "This node
represents a concatenation comparison operator"? The concatenation operator is
not a comparison operator.
> Support more than just varchar with vertical bars on query
> ----------------------------------------------------------
>
> Key: DERBY-1306
> URL: http://issues.apache.org/jira/browse/DERBY-1306
> Project: Derby
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 10.1.2.1
> Environment: Relevant for this? Windows XP
> Reporter: Bill Robertson
>
> I'm not sure if this is ij or derby proper, but the concat operator || should
> work for just about any data type. Derby is zero maintenance, but data
> rarely is, and a good sql interface is important. Often it's very convenient
> to write a query that generates other sql statements and that's difficult w/o
> concatination.
> e.g. create a table with a timestamp column, assume that the column name is
> originated.
> Try the following query:
> ij> select month(originated) || '-' || year(originated) from review;
> get the following error:
> ERROR 42846: Cannot convert types 'INTEGER' to 'VARCHAR'.
> The conversion to a string should pretty much work all the time unless the
> operand is some sort of blob type.
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