Hello,

I found the following result from a sample
(the VARCHAR(10) column is CHARSET UNICODE_FSS)

Database MetaData (interclient)

type COLUMN_SIZE DECIMAL_DIGITS

VARCHAR(10) 30 0
INTEGER 10 0
DECIMAL(11,2) 19 2
DECIMAL(5,4) 10 4
DATE 10 0
TIME 8 0
TIMESTAMP 19 0

ResultSet MetaData (interclient)

type getColumnDisplaySize getPrecision getScale

VARCHAR(10) 10 10 0
INTEGER 11 10 0
DECIMAL(11,2) 22 19 2
DECIMAL(5,4) 13 10 4
DATE 10 10 0
TIME 8 8 0
TIMESTAMP 19 19 0

Database MetaData (firebirdsql)

type COLUMN_SIZE DECIMAL_DIGITS

VARCHAR(10) 30 0
INTEGER 4 0
DECIMAL(11,2) 11 2
DECIMAL(5,4) 5 4
DATE 4 0
TIME 4 0
TIMESTAMP 8 0

ResultSet MetaData (firebirdsql)

type getColumnDisplaySize getPrecision getScale

VARCHAR(10) 30 30 0
INTEGER 4 4 0
DECIMAL(11,2) 8 8 2
DECIMAL(5,4) 4 4 4
DATE 10 4 0
TIME 4 4 0
TIMESTAMP 8 8 0

Then I read the API documentation, and find the result

Database MetaData
* COLUMN_SIZE int => column size. For char or date types this is the
maximum number of characters, for numeric or decimal types this is
precision.
* BUFFER_LENGTH is not used.
* DECIMAL_DIGITS int => the number of fractional digits

ResultSet MetaData
* getColumnDisplaySize() => the normal maximum width in characters
* getPrecison() => the number of decimal digits
* getScale() => the number of digits to right of the decimal point

So, I have the following comment:
* VARCHAR(10) - In terms of COLUMN_SIZE, it should be 10 (characters).
In terms of buffer size, as it is defined as CHARSET UNICODE_FSS, in
Firebird, it is stored in UTF8, so the maximum allowd size is 30 (bytes)
Depend on the fonts, display size may be 20 (for most
caes of double-byte characters)
* INTEGER - the maximum value is 2147483648. So it is 10 digits width,
but in case of precision, COLUMN_SIZE should be 9 (decimal digits)
while display size is 11 characters (10 + 1 for sign)
firebirdsql is wrong, as 4 (bytes) is the buffer size but
not the precision or display size
* DECIMAL(11,2) - COLUMN_SIZE should be 11 (precision), display size
should be 13 (11 + 1 for sign + 1 for decimal point). If it is stored
as double, buffer size is 8 (bytes)
interclient returns miserable figure.
firebirdsql is right for database metadata, but wrong
for resultset metadata.
* DECIMAL(5,4) - COLUMN_SIZE should be 5 (precision), display size
should be 7 (5 + 1 for sign + 1 for decimal point). If it is stored
as float, buffer size is 4 (bytes)
interclient returns miserable figure.
firebirdsql is right for database metadata, but wrong
for resultset metadata.
* DATE - the ISO format for SQL date is YYYY-MM-DD. So COLUMN_SIZE and
display size is 10. The buffer size in bytes depends on database
implmentation.
* TIME - the ISO format for SQL time is HH:MM:SS. So COLUMN_SIZE and
display size is 8. The buffer size in bytes depends on database
implementation.
* TIMESTAMP - the ISO format for SQL timestamp is
YYYY-MM-DD.HH:MM:SS.SSSSSS. So COLUMN_SIZE and display size is 26.
The buffer size in bytes depends on database implementation.

Display size, precision, scale, and number of bytes for data items are
the fundamental of computer data processing.
Be careful, in terms of UNICODE, or multi-byte characters, the number
of characters and number of bytes is different.

So the result should be as follows

Database MetaData

type COLUMN_SIZE DECIMAL_DIGITS BUFFER_LENGTH

VARCHAR(10) 10 0 30
INTEGER 9 0 4
DECIMAL(11,2) 11 2 8 (if stored as dobule)
DECIMAL(5,4) 5 4 4 (if stored as float)
DATE 10 0 10 (if stored as character), 8
(if stored as long)
TIME 8 0 8 (if stored as character or long)
TIMESTAMP 26 0 26 (if stored as character), 8
(if stored as long)

ResultSet MetaData

type getColumnDisplaySize getPrecision getScale

VARCHAR(10) 20 10 0
INTEGER 11 9 0
DECIMAL(11,2) 13 11 2
DECIMAL(5,4) 7 5 4
DATE 10 10 0
TIME 8 8 0
TIMESTAMP 26 26 0

BUFFER_LENGTH depends on internal representation of the data, so it is
vendor dependent.
But COLUMN_SIZE, DECIMAL_DIGITS, getColumnDisplaySize, getPrecision,
getScale (I think) should be vendor independent, and consistent with
the value used in CREATE TABLE.
Please check if interclient and firebirdsql returns incorrect value.
And a patch is appreciated.

Thanks

CN