[Firebird-devel] [ firebird-Bugs-412417 ] altering from CHAR to VARCHAR

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Bugs item #412417, was updated on 2001-03-30 01:12
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Category: Data Types/On-Disk Struc(ODS)
Group: None
Status: Open
Priority: 5
Submitted By: Dmitri Kouzmenko (kdv)
Assigned to: Nobody/Anonymous (nobody)
Summary: altering from CHAR to VARCHAR

Initial Comment:
Altering CHAR to VARCHAR column adds 2 bytes to field length.

How to reproduce:

CREATE TABLE TEST( N CHAR(40));

then

ALTER TABLE TEST ALTER N TYPE VARCHAR(40);

after that RDB$FIELD_LENGTH will be 42, not 40 as it should be.
RDB$CHARACTER_LENGTH is Ok, i.e. it stays 40 after ALTER.

The '40' is not a magic number - same addition of 2 bytes will be for any altering
from char to varchar. For example, altering char(40) to varchar(50) will give
the resulting varchar field 52 characters length.

Tested with FireBird 0.9.4 for Windows (NT 4.0 SP6a workstation). Dialect 3 database.

p.s. real varchar storage size is 2 bytes greater than char. But, column length definition
(RDB$FIELD_LENGTH) does not store physical field lenght - it stores column length.
So, altering char to varchar must keep the same column size.

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