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Firebird Interview Questions & Answers - Learning Mode

Firebird Interview Questions & Answers - Learning Mode

Firebird is a relational database offering many ANSI SQL standard features that runs on Linux, Windows, and a variety of Unix platforms. Firebird offers excellent concurrency, high performance, and powerful language support for stored procedures and triggers. Firebird is an open source SQL relational database management system that runs on Linux, Microsoft Windows, Mac OS X and a variety of Unix. The database forked from Borland's open source edition of InterBase in 2000, but since Firebird 1.5 the code has been largely rewritten. Initial release‎: ‎2000.

Try Firebird Interview Questions & Answers - Exam Mode

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Firebird Interview Questions & Answers - Learning Mode
Try Firebird Interview Questions & Answers - Exam Mode
Question: How to deactivate triggers?

Answer: You can use these SQL commands:


Most tools have options to activate and deactivate all triggers for a table. For example, in FlameRobin, open the properties screen for a table, click on Triggers at top and then Activate or Deactivate All Triggers options at the bottom of the page. Source:
Question: How to select a random record from a table?

Answer: There is no such feature in Firebird, but you can use some tricks. The following example requires that you have a unique integer column (primary key is usually used):

SELECT ...field_list...
FROM table t1
WHERE conditions
ORDER BY (t1.int_col + seed)*4294967291-((t1.int_col + seed)*4294967291/49157)*49157;

If you just need one random record, limit the result set using FIRST or ROWS clause. This query will give consistent records for the same seed. If you wish to be complet Source:
Question: How to use events with ZeBeDee, SSH or stunnel?

Answer: You have to use SuperServer, set up RemoteAuxPort setting in firebird.conf and create two tunnels (one for data, other for events). Source:
Question: How to configure events with firewall?

Answer: If firewall is on client, you don't have to do anything special. If firewall is on the server, you need to set RemoteAuxPort setting in Firebird.conf file and forward traffic from firewall to that port. Source:
Question: How to stop SuperServer service on Linux using only Firebird tools?

Answer: The server is started and stopped by 'fbmgr' executable from 'bin' directory of your Firebird installation. It is called 'ibmgr' in Firebird 1.0. To start the server type:

/opt/firebird/bin/fbmgr -start

To start the server with Guardian (Guardian watches the server and restarts it if it crashes) type:

/opt/firebird/bin/fbmgr -start -forever

To stop a running server, type:

/opt/firebird/bin/fbmgr -shut -user SYSDBA -pass *****

To f Source:
Question: How to specify transaction or query timeout?

Answer: In order to keep the server low reasonable, you might want to limit the time a single query can consume. Firebird does not support this directly yet (there are plans for Firebird 3.0).

However, you could periodically query the monitoring tables (Firebird 2.1 and above) to detect and cancel long running queries. You can do:


Look for those having MON$STATE set to 1.

Please note that your database needs to be at least ODS 11.1, i.e. created Source:
Question: How to do replication of Firebird databases?

Answer: Firebird does not offer replication out-of-the-box, you need to use some 3rd party tools. Those external tools add specific triggers that log all the changes in database and replicate to other databases.
Question: Is there an example how to configure UdfAccess setting in firebird.conf?

Answer: Well, there's one right there in the firebird.conf, but perhaps it isn't obvious enough. Here are the basic settings ('None' to disallow UDFs completely and 'Full' to allow them anywhere) which you probably understood yourself:

UdfAccess = None
UdfAccess = Full

And here is that tricky Restrict setting:

UdfAccess = Restrict C:somedirectory

For multiple directories, use something like this:

UdfAccess = Restrict C:somedirectory;C:someoth Source:
Question: How to create a database from my program?

Answer: Firebird doesn't provide a way to create database using SQL. You need to either use the Services API, or external tool. As API for database creation is often not available in libraries, you can call Firebird's isql tool to do it for you.

Let's first do it manually. Run the isql, and then type:

SQL>CREATE DATABASE 'C:dbasesdatabase.fdb' user 'SYSDBA' password 'masterkey';

That's it. Database is created. Type exit; to leave isql.< Source:
Question: Why does reading require write privileges on database file?

Answer: In order to run the SELECT statmement, it still needs to start a transaction.

If you wish to build a read-only database to place on some read-only media like CD or DVD ROM, you can do it with:

gfix -mode read_only database.fdb

...or within your favorite administration tool. It is also available via ServicesAPI, so you may do it from your application as well. Please note that you can only make this change while preparing the database, because the read-only flag needs to be wr Source:
Question: How to migrate Paradox, dBase or FoxPro database to Firebird?

Answer: The easiest way is to download the freeware IBDataPump by CleverComponents. It will extract the metadata from Paradox/dBase/FoxPro database, create all the tables in a Firebird database and then copy all the data. You'll probably have a ready-to-go Firebird database in less than one hour. Source:
Question: How to tell Firebird to only accept conections from XYZ host or network?

Answer: This isn't really a thing you should be configuring in Firebird. There is a RemoteBindAddress setting in firebird.conf which configures on which interfaces/addresses the Firebird listens but that's all. You should really use your system's firewall to set this up.

Beside firewall, if you use Classic on Linux, you can use xinetd or inetd access control files /etc/hosts.allow and /etc/hosts.deny. With xinetd you can also edit the xinetd configuration file for Firebird service, wh Source:
Question: How to repair a corrupt Firebird database?

Answer: Here's a short step-by-step walkthrough:

* disconnect users and disable incoming connections to the database
* make a copy of database file (or two copies) and work on that
* use GFIX with -v option to validate the database file
* use GFIX with -v and -f to do full validation

If problem is not too serious, you can try to backup the broken db and restore under a new name:

* use GFIX -mend to prepare corrupt database for backup
* use GBAK -b -g to backup the da Source:
Question: How to detect applications and users that hold transactions open too long?

Answer: To do this, you need Firebird 2.1 or a higher version. First, run gstat tool (from your Firebird installation's bin directory), and you'll get an output like this:

gstat -h faqs.gdb

Database "faqs.gdb"
Database header page information:
Flags 0
Checksum 12345
Generation 919
Page size 4096
ODS version 11.1
Oldest transaction 812
Oldest active 813
Oldest snapshot 813
Next transaction 814

Now, connect to that database and query the MON$TRANS Source:
Question: How to debug stored procedures?

Answer: Firebird still doesn't offer hooks for stored procedure debugging yet. Here are some common workarounds:

* You can log values of your variables and trace the execution via external tables. External tables are not a subject of transaction control, so the trace won't be lost if transaction is rolled back.

* You can turn your non-selectable stored procedure into selectable and run it with 'SELECT * FROM' instead of 'EXECUTE PROCEDURE' in order to trace the exec Source:
Question: How to determine who is and change the owner of database?

Answer: Use the following query:


Please note that in order to change the owner, it is not enough (or even advisable) to change this column only, as many other metadata fields are involved (there are multiple tables which have this field and SQL privileges need to be updated as well). There is a handy tool by Thomas Steinmaurer that can do this automatically, but you'll have to e-mail Source:
Question: How to lock records in a table?

Answer: While there shouldn't be many reasons to do this in MGA database system like Firebird, there are ways to do it.

One is to use a dummy update for all the records you wish to lock. Many developers do this by accident and get the deadlocks. Example that locks employee 8:

-- start transaction
update employee set emp_no = emp_no where emp_no = 8;
update employee set ... where emp_no = 8;
-- end transaction

A more elegant way is to use the SELECT ... WITH L Source:
Question: What is command for supporting foreign key in Firebird?

Answer: Lets do it by example:

create table Master_A( mst_1 integer not null primary key,
mst_2 varchar(10));

create table slave_of_a(slv_1 integer not null, primary key,
mst_1 integer);

alter table slave_of_a add constraint FK_2_MST foreign key (mst_1) references Master_A(mst_1);

Is the same command that sql92 supports.

alter table table_name add constraint constraint_name foreign key (field1,field2,...) references
master_table(field1,field2...,); Source:
Question: How to load a file into database column?

Answer: While some other database systems might have an SQL function for this, with Firebird you need an application. Datatype that holds binary files is called BLOB, and you should use sub_type zero, as sub_type one is for text-only data. Let's create a table to hold the file. We'll have a filename column and a blob column containing the file itself:

file_name VARCHAR(200),
file_data BLOB SUB_TYPE 0

The blobs are loaded via parametrized query:
< Source:
Question: Is there a way to detect whether fbclient.dll or fbembed.dll is loaded?

Answer: There are some ways to detect it:

- check the size of DLL file

- if you are using different versions of Firebird (for example 1.5.4 and 2.0.1, you can query the server version via Services API)

You should understand that fbembed can be used as a regular Firebird client. Checking whether embedded or fbclient is loaded for licensing or similar needs is really not useful. You could use the connection string as guide, but super server can establish direct local connections witho Source:

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