How can I get the table description (fields and types) from Firebird with dbExpress - delphi

Question

I have written a tool for displaying database structures using the GetTableNames and GetFieldNames methods of TSQLConnection. How can I get the types of each field name similar to the following list (which is part of the DDL required to build the table)?
TABLE: ARTICLES
ID INTEGER NOT NULL
PRINTED SMALLINT DEFAULT 0
ACADEMIC SMALLINT
RELEVANCE SMALLINT
SOURCE VARCHAR(64) CHARACTER SET WIN1251 COLLATE WIN1251
NAME VARCHAR(128) CHARACTER SET WIN1251 COLLATE WIN1251
FILENAME VARCHAR(128) CHARACTER SET WIN1251 COLLATE WIN1251
NOTES VARCHAR(2048) CHARACTER SET WIN1251 COLLATE WIN1251

Answer 1

This is incomplete (because I've never used Firebird array data types) and not much tested but perhaps it will give you a good starting point:
SELECT
RF.RDB$FIELD_NAME FIELD_NAME,
CASE F.RDB$FIELD_TYPE
WHEN 7 THEN
CASE F.RDB$FIELD_SUB_TYPE
WHEN 0 THEN 'SMALLINT'
WHEN 1 THEN 'NUMERIC(' || F.RDB$FIELD_PRECISION || ', ' || (-F.RDB$FIELD_SCALE) || ')'
WHEN 2 THEN 'DECIMAL'
END
WHEN 8 THEN
CASE F.RDB$FIELD_SUB_TYPE
WHEN 0 THEN 'INTEGER'
WHEN 1 THEN 'NUMERIC(' || F.RDB$FIELD_PRECISION || ', ' || (-F.RDB$FIELD_SCALE) || ')'
WHEN 2 THEN 'DECIMAL'
END
WHEN 9 THEN 'QUAD'
WHEN 10 THEN 'FLOAT'
WHEN 12 THEN 'DATE'
WHEN 13 THEN 'TIME'
WHEN 14 THEN 'CHAR(' || (TRUNC(F.RDB$FIELD_LENGTH / CH.RDB$BYTES_PER_CHARACTER)) || ') '
WHEN 16 THEN
CASE F.RDB$FIELD_SUB_TYPE
WHEN 0 THEN 'BIGINT'
WHEN 1 THEN 'NUMERIC(' || F.RDB$FIELD_PRECISION || ', ' || (-F.RDB$FIELD_SCALE) || ')'
WHEN 2 THEN 'DECIMAL'
END
WHEN 27 THEN 'DOUBLE'
WHEN 35 THEN 'TIMESTAMP'
WHEN 37 THEN 'VARCHAR(' || (TRUNC(F.RDB$FIELD_LENGTH / CH.RDB$BYTES_PER_CHARACTER)) || ')'
WHEN 40 THEN 'CSTRING' || (TRUNC(F.RDB$FIELD_LENGTH / CH.RDB$BYTES_PER_CHARACTER)) || ')'
WHEN 45 THEN 'BLOB_ID'
WHEN 261 THEN 'BLOB SUB_TYPE ' || F.RDB$FIELD_SUB_TYPE
ELSE 'RDB$FIELD_TYPE: ' || F.RDB$FIELD_TYPE || '?'
END FIELD_TYPE,
IIF(COALESCE(RF.RDB$NULL_FLAG, 0) = 0, NULL, 'NOT NULL') FIELD_NULL,
CH.RDB$CHARACTER_SET_NAME FIELD_CHARSET,
DCO.RDB$COLLATION_NAME FIELD_COLLATION,
COALESCE(RF.RDB$DEFAULT_SOURCE, F.RDB$DEFAULT_SOURCE) FIELD_DEFAULT,
F.RDB$VALIDATION_SOURCE FIELD_CHECK,
RF.RDB$DESCRIPTION FIELD_DESCRIPTION
FROM RDB$RELATION_FIELDS RF
JOIN RDB$FIELDS F ON (F.RDB$FIELD_NAME = RF.RDB$FIELD_SOURCE)
LEFT OUTER JOIN RDB$CHARACTER_SETS CH ON (CH.RDB$CHARACTER_SET_ID = F.RDB$CHARACTER_SET_ID)
LEFT OUTER JOIN RDB$COLLATIONS DCO ON ((DCO.RDB$COLLATION_ID = F.RDB$COLLATION_ID) AND (DCO.RDB$CHARACTER_SET_ID = F.RDB$CHARACTER_SET_ID))
WHERE (RF.RDB$RELATION_NAME = :TABLE_NAME) AND (COALESCE(RF.RDB$SYSTEM_FLAG, 0) = 0)
ORDER BY RF.RDB$FIELD_POSITION;

Answer 2

Use direct access to RDB$ tables. For example:
SELECT * FROM rdb$relations
will give you a list of all tables in a database.
SELECT
*
FROM
rdb$relation_fields rf JOIN rdb$fields f
ON f.rdb$field_name = rf.rdb$field_source
WHERE
rf.rdb$relation_name = :RN
will result in a list of all fields of given table
with information of field type. Param RN is a name of the table.
Using information from RDB$tables one can easily construct DDL
statement. The query below gives you a hint how to do it:
SELECT
TRIM(rf.rdb$field_name) || ' ' ||
IIF(rdb$field_source LIKE 'RDB$%',
DECODE(f.rdb$field_type,
8, 'INTEGER',
12, 'DATE',
37, 'VARCHAR',
14, 'CHAR',
7, 'SMALLINT'),
TRIM(rdb$field_source)) ||
IIF((rdb$field_source LIKE 'RDB$%') AND (f.rdb$field_type IN (37, 14)),
'(' || f.rdb$field_length || ')',
'') ||
IIF((f.rdb$null_flag = 1) OR (rf.rdb$null_flag = 1),
' NOT NULL', '')
FROM
rdb$relation_fields rf JOIN rdb$fields f
ON f.rdb$field_name = rf.rdb$field_source
WHERE
rf.rdb$relation_name = '<put_your_table_name_here>'

Answer 3

Using the link which TLama provided, I found my own solution, which is somewhat similar to the above solutions, but simpler.
SELECT R.RDB$FIELD_NAME AS field_name,
CASE F.RDB$FIELD_TYPE
WHEN 7 THEN 'SMALLINT'
WHEN 8 THEN 'INTEGER'
WHEN 9 THEN 'QUAD'
WHEN 10 THEN 'FLOAT'
WHEN 11 THEN 'D_FLOAT'
WHEN 12 THEN 'DATE'
WHEN 13 THEN 'TIME'
WHEN 14 THEN 'CHAR'
WHEN 16 THEN 'INT64'
WHEN 27 THEN 'DOUBLE'
WHEN 35 THEN 'TIMESTAMP'
WHEN 37 THEN 'VARCHAR'
WHEN 40 THEN 'CSTRING'
WHEN 261 THEN 'BLOB'
ELSE 'UNKNOWN'
END AS field_type,
F.RDB$FIELD_LENGTH AS field_length,
CSET.RDB$CHARACTER_SET_NAME AS field_charset
FROM RDB$RELATION_FIELDS R
LEFT JOIN RDB$FIELDS F ON R.RDB$FIELD_SOURCE = F.RDB$FIELD_NAME
LEFT JOIN RDB$CHARACTER_SETS CSET ON F.RDB$CHARACTER_SET_ID = CSET.RDB$CHARACTER_SET_ID
WHERE R.RDB$RELATION_NAME= :p1
ORDER BY R.RDB$FIELD_POSITION
p1 is the table name which is passed as a parameter to the query.
In context, I have a treeview which has as its nodes the table names of a given database; for each node, the child nodes are the fields along with their definitions.
sqlcon.GetTableNames (dbTables); // sqlcon is the TSQLConnection
tv.items.Clear;
for i:= 1 to dbTables.count do
begin
node:= tv.items.Add (nil, dbTables[i - 1]);
with qFields do // the above query
begin
params[0].asstring:= dbTables[i - 1];
open;
while not eof do
begin
tv.items.addchild (node, trim (fieldbyname ('field_name').asstring) + ', ' +
trim (fieldbyname ('field_type').asstring) + ', ' +
fieldbyname ('field_length').asstring + ', ' +
fieldbyname ('field_charset').asstring);
next
end;
close
end
end;
Here is a screenshot of the program in action. I realise that the format is not the same as the DDL which I quoted, but it's obvious what each field means (at least to me, and this is a program for my private use).

Answer 4

I made a litle change to the first option to support computed by fields, add field_position and made a view to make more easy.
CREATE VIEW TABLES (
TABLE_NAME,
FIELD_NAME,
FIELD_POSITION,
FIELD_TYPE,
FIELD_NULL,
FIELD_CHARSET,
FIELD_COLLATION,
FIELD_DEFAULT,
FIELD_CHECK,
FIELD_DESCRIPTION
)
AS
SELECT
RF.RDB$RELATION_NAME,
RF.RDB$FIELD_NAME FIELD_NAME,
RF.RDB$FIELD_POSITION FIELD_POSITION,
CASE F.RDB$FIELD_TYPE
WHEN 7 THEN
CASE F.RDB$FIELD_SUB_TYPE
WHEN 0 THEN 'SMALLINT'
WHEN 1 THEN 'NUMERIC(' || F.RDB$FIELD_PRECISION || ', ' || (-F.RDB$FIELD_SCALE) || ')'
WHEN 2 THEN 'DECIMAL'
END
WHEN 8 THEN
CASE F.RDB$FIELD_SUB_TYPE
WHEN 0 THEN 'INTEGER'
WHEN 1 THEN 'NUMERIC(' || F.RDB$FIELD_PRECISION || ', ' || (-F.RDB$FIELD_SCALE) || ')'
WHEN 2 THEN 'DECIMAL'
END
WHEN 9 THEN 'QUAD'
WHEN 10 THEN 'FLOAT'
WHEN 12 THEN 'DATE'
WHEN 13 THEN 'TIME'
WHEN 14 THEN 'CHAR(' || (TRUNC(F.RDB$FIELD_LENGTH / CH.RDB$BYTES_PER_CHARACTER)) || ') '
WHEN 16 THEN
CASE F.RDB$FIELD_SUB_TYPE
WHEN 0 THEN 'BIGINT'
WHEN 1 THEN 'NUMERIC(' || F.RDB$FIELD_PRECISION || ', ' || (-F.RDB$FIELD_SCALE) || ')'
WHEN 2 THEN 'DECIMAL'
END
WHEN 27 THEN 'DOUBLE'
WHEN 35 THEN 'TIMESTAMP'
WHEN 37 THEN
IIF (COALESCE(f.RDB$COMPUTED_SOURCE,'')<>'',
'COMPUTED BY ' || CAST(f.RDB$COMPUTED_SOURCE AS VARCHAR(250)),
'VARCHAR(' || (TRUNC(F.RDB$FIELD_LENGTH / CH.RDB$BYTES_PER_CHARACTER)) || ')')
WHEN 40 THEN 'CSTRING' || (TRUNC(F.RDB$FIELD_LENGTH / CH.RDB$BYTES_PER_CHARACTER)) || ')'
WHEN 45 THEN 'BLOB_ID'
WHEN 261 THEN 'BLOB SUB_TYPE ' || F.RDB$FIELD_SUB_TYPE
ELSE 'RDB$FIELD_TYPE: ' || F.RDB$FIELD_TYPE || '?'
END FIELD_TYPE,
IIF(COALESCE(RF.RDB$NULL_FLAG, 0) = 0, NULL, 'NOT NULL') FIELD_NULL,
CH.RDB$CHARACTER_SET_NAME FIELD_CHARSET,
DCO.RDB$COLLATION_NAME FIELD_COLLATION,
COALESCE(RF.RDB$DEFAULT_SOURCE, F.RDB$DEFAULT_SOURCE) FIELD_DEFAULT,
F.RDB$VALIDATION_SOURCE FIELD_CHECK,
RF.RDB$DESCRIPTION FIELD_DESCRIPTION
FROM RDB$RELATION_FIELDS RF
JOIN RDB$FIELDS F ON (F.RDB$FIELD_NAME = RF.RDB$FIELD_SOURCE)
LEFT OUTER JOIN RDB$CHARACTER_SETS CH ON (CH.RDB$CHARACTER_SET_ID = F.RDB$CHARACTER_SET_ID)
LEFT OUTER JOIN RDB$COLLATIONS DCO ON ((DCO.RDB$COLLATION_ID = F.RDB$COLLATION_ID) AND (DCO.RDB$CHARACTER_SET_ID = F.RDB$CHARACTER_SET_ID))
WHERE (COALESCE(RF.RDB$SYSTEM_FLAG, 0) = 0)
ORDER BY RF.RDB$FIELD_POSITION
;