How do I test if a table exists in Interbase? - delphi

Question

I have just recently started using Interbase, and I need to verify if the database has a table, how do I check in Interbase if a table exists in the database?

Answer 1

For IBX there are at least these ways disponible:
1. Using SQL query
You can query the RDB$RELATIONS system table in which you filter by the RDB$RELATION_NAME column. For example this query returns 1 when table called MyTable exists in the database:
SELECT 1 FROM RDB$RELATIONS
WHERE RDB$RELATION_NAME = 'MyTable'
With IBX on client side you can write for instance this:
function TableExists(Database: TIBDatabase; const TableName: string): Boolean;
var
Query: TIBSQL;
begin
Query := TIBSQL.Create(Database);
try
Query.SQL.Text := 'SELECT 1 FROM RDB$RELATIONS WHERE RDB$RELATION_NAME = ?';
Query.Params[0].AsString := TableName;
Query.ExecQuery;
{ RecordCount reports only visited records, so it should be either 0 or 1 now }
Result := Query.RecordCount > 0;
finally
Query.Free;
end;
end;
This version is case sensitive and is efficient when you need to determine if table exists from code only ocassionally (for checking frequently I would cache the list of all table names returned by the GetTableNames method and query just such list).
2. Using TIBDatabase.GetTableNames method
The TIBDatabase class is able to list all the table names by the GetTableNames method. In the returned string list collection you can then verify if the name exists by the IndexOf method. For example:
function TableExists(Database: TIBDatabase; const TableName: string): Boolean;
var
Tables: TStrings;
begin
Tables := TStringList.Create;
try
Database.GetTableNames(Tables, True);
Result := Tables.IndexOf(TableName) <> -1;
finally
Tables.Free;
end;
end;
This version is case insensitive (so long you won't change the default value of the CaseSensitive property of the returned collection) and is naturally not as efficient as the first way for single or ocassional use because this one fetches the whole table name collection from server to client. But the GetTableNames method itself can be useful for frequent use if you cache the returned collection.
3. Using TIBExtract class
The TIBExtract IBX class is intended for fetching metadata. Unfortunately it't not so efficient and easy to use for just checking whether certain table exists in database because it can fetch either list of all tables, or details of the table itself. So I leave this option without example.