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Working with databases

Connection strings
Connecting to an existing database
Creating a database using isql
Firebird SQL

In this part of the manual you will learn:

In as much as remote connections are involved, we will use the recommended TCP/IP protocol.

Connection strings

If you want to connect to a database or create one you have to supply, amongst other things, a connection string to the client application (or, if you are a programmer, to the routines you are calling). A connection string uniquely identifies the location of the database on your computer, local network, or even the Internet.

Local connection strings

An explicit local connection string consists of the path + filename specification in the native format of the filesystem used on the server machine, for example

  • on a Linux or other Unix-like server:


  • on a Windows server:


Many clients also allow relative path strings (e.g. “..\examples\empbuild\employee.fdb”) but you should use these with caution, as it's not always obvious how they will be expanded. Getting an error message is annoying enough, but applying changes to another database than you thought you were connected to may be disastrous.

Instead of a file path, the local connection string may also be a database alias that is defined in aliases.conf, as mentioned earlier. The format of the alias depends only on how it's defined in the aliases file, not on the server filesystem. Examples are:

  • zappa

  • blackjack.fdb

  • poker

Upon receiving a local connection string, the Firebird client will first attempt to make a direct, embedded connection to the database file, bypassing authentication but respecting the SQL privileges and restrictions of the supplied user and/or role name. That is, if the Engine12 provider is enabled in firebird.conf or databases.conf – which it is by default. If the database file exists but the connection fails because the client process doesn't have the required access privileges to the file, a client-server connection is attempted (by the Loopback provider), in this order:

  1. Using TCP/IP via localhost;

  2. On Windows: using WNET (NetBEUI), aka Named Pipes, on the local machine;

  3. On Windows: using XNET (shared memory) on the local machine.

You can force Firebird to use a certain protocol (and skip the embedded connection attempt) by prepending the protocol in URL style:

  • inet://zappa (TCP/IP connection using an alias on the local machine)

  • inet:///opt/firebird/examples/citylife.fdb (TCP/IP connection using an absolute path on the local Posix machine – notice the extra slash for the root dir)

  • inet://C:\Work\Databases\Drills.fdb (TCP/IP connection using an absolute path on the local Windows machine)

  • wnet://doggybase (NetBEUI – named pipes – connection using an alias on the local Windows machine)

  • wnet://D:\Fun\Games.fdb (NetBEUI – named pipes – connection using an absolute path on the local Windows machine)

  • xnet://security.db (XNET connection using an alias on the local Windows machine)

  • xnet://C:\Programmas\Firebird\Firebird_3_0\security3.fdb (XNET connection using the full path on the local Windows machine)


If your XNET connections fail, it may be because the local protocol isn't working properly on your machine. If you're running Windows Vista, 2003 or XP with terminal services enabled, this can often be fixed by setting IpcName to Global\FIREBIRD in the configuration file firebird.conf (don't forget to uncomment the parameter and restart the server).

If setting IpcName doesn't help and you don't get the local protocol enabled, you can usually work around the problem by using inet://, wnet://, or putting “localhost:” before your database paths or aliases, thus turning them into TCP/IP connection strings (discussed below).

TCP/IP connection strings

A TCP/IP connection string consists of:

  1. a server name or IP address

  2. an optional slash (“/”) plus port number or service name

  3. a colon (“:”)

  4. either the absolute path + filename on the server machine, or an alias defined on the server machine.


  • On Linux/Unix:




  • On Windows:




Notice how the aliased connection strings don't give any clue about the server OS. And they don't have to, either: you talk to a Linux Firebird server just like you talk to a Windows Firebird server. In fact, specifying an explicit database path is one of the rare occasions where you have to be aware of the difference.

NetBEUI connection strings

A NetBEUI (named pipes) connection string consists of:

  1. two backslashes (“\\”)

  2. a server name or IP address

  3. an optional at sign (“@”) plus port number or service name

  4. another backslash (“\”)

  5. either the absolute path + filename on the server machine, or an alias defined on the server machine.


  • On Windows, the exact same databases as in the TCP/IP examples:





URL-style connection strings

Local URL-style connection strings have already been introduced.

A remote URL-style connection string consists of:

  1. a protocol name (inet or wnet) followed by a colon and two slashes (“://”)

  2. a server name or IP address

  3. an optional colon (“:”) plus port number or service name

  4. a slash (“/”)

  5. either the absolute path + filename on the server machine, or an alias defined on the server machine.


  • On Linux/Unix:





  • On Windows:





Since XNET is a purely local protocol, you can't have remote connection strings starting with xnet://.

Third-party programs

Please be aware that some third-party client programs may have different requirements for the composition of connection strings. Refer to their documentation or online help to find out.

Connecting to an existing database

A sample database named employee.fdb is located in the examples/empbuild subdirectory of your Firebird installation. It is also reachable under its alias employee. You can use this database to “try your wings”.

If you move or copy the sample database, be sure to place it on a hard disk that is physically attached to your server machine. Shares, mapped drives or (on Unix) mounted SMB (Samba) file systems will not work. The same rule applies to any databases that you create or use.

Connecting to a Firebird database requires – implicit or explicit – authentication. In order to work with objects inside the database, such as tables, views and functions, you (i.e. the Firebird user you're logged in as) need explicit permissions on those objects, unless you own them (you own an object if you have created it) or if you're connected as user SYSDBA or with the role RDB$ADMIN. In the example database employee.fdb, sufficient permissions have been granted to PUBLIC (i.e. anybody who cares to connect) to enable you to view and modify data to your heart's content.

For simplicity here, we will look at authenticating as SYSDBA using the password masterkey. Also, to keep the lines in the examples from running off the right edge, we will work with local databases and use aliases wherever possible. Of course everything you'll learn in these sections can also be applied to remote databases, simply by supplying a full TCP/IP connection string.

Connecting with isql

Firebird ships with a text-mode client named isql (Interactive SQL utility). You can use it in several ways to connect to a database. One of them, shown below, is to start it in interactive mode. Go to the directory where the Firebird tools reside (see Default disk locations if necessary) and type isql (Windows) or ./isql (Linux) at the command prompt.

[In the following examples, ↵ means “hit Enter”]

Use CONNECT or CREATE DATABASE to specify a database
SQL>connect xnet://employee user sysdba password masterkey;↵


  • In isql, every SQL statement must end with a semicolon. If you hit Enter and the line doesn't end with a semicolon, isql assumes that the statement continues on the next line and the prompt will change from SQL> to CON>. This enables you to split long statements over multiple lines. If you hit Enter after your statement and you've forgotten the semicolon, just type it after the CON> prompt on the next line and press Enter again.

  • If the connection string doesn't start with a host or protocol name, a direct serverless connection to the database is attempted. This may fail if your OS login doesn't have sufficient access rights to the database file. In that case, connect to localhost:path-or-alias or specify a protocol like xnet:// (Windows only) or inet://. Then the server process (usually running as user firebird on Posix or LocalSystem on Windows) will open the file. On the other hand, network-style connections may fail if a user created the database in direct-access mode and the server doesn't have enough access rights.


You can optionally enclose the path, the user name and/or the password in single (') or double (") quotes. If the path contains spaces, quoting is mandatory. Case-sensitive user names (created like this: create user "Jantje" password ...) and user names with spaces, international characters or other “funny stuff” also need to be double-quoted.

At this point, isql will inform you that you are connected:

Database: xnet://employee, User: SYSDBA

You can now continue to play about with the employee database. With isql you can query data, get information about the metadata, create database objects, run data definition scripts and much more.

To get back to the OS command prompt, type:


You can also type EXIT instead of QUIT, the difference being that EXIT will first commit any open transactions, making your modifications permanent.

Connecting with a GUI client

Some GUI client tools take charge of composing the CONNECT string for you, using server, path (or alias), user name and password information that you type into prompting fields. Supply the various elements as described in the preceding topic.


  • It is also quite common for such tools to expect the entire server + path/alias as a single connection string – just like isql does.

  • Remember that file names and commands on Linux and other Unix-like platforms are case-sensitive.

Creating a database using isql

There is more than one way to create a database with isql. Here, we will look at one simple way to create a database interactively – although, for your serious database definition work, you should create and maintain your metadata objects using data definition scripts.

Starting isql

To create a database interactively using the isql command shell, type isql (Windows) or ./isql (Linux) at the command prompt in the directory where the Firebird tools are.

[In the following examples, ↵ means “hit Enter”]

Use CONNECT or CREATE DATABASE to specify a database


Now you can create your new database interactively. Let's suppose that you want to create a database named test.fdb and store it in a directory named data on your D drive:

SQL>create database 'D:\data\test.fdb' page_size 8192↵
CON>user 'sysdba' password 'masterkey';↵


  • In the CREATE DATABASE statement it is mandatory to place quote characters (single or double) around path and password. This is different from the CONNECT statement. Quoting the user name is optional, unless it is case-sensitive or contains spaces, international characters or any other character that is not allowed in an unquoted identifier.

  • If the connection string doesn't start with a host or protocol name, creation of the database file is attempted with your OS login as the owner. This may or may not be what you want (think of access rights if you want others to be able to connect). If you prepend localhost: or a protocol to the path or alias, the server process will create and own the file.

The database will be created and, after a few moments, the SQL prompt will reappear. You are now connected to the new database and can proceed to create some test objects in it.

But to verify that there really is a database there, let's first type in this query:

SQL>select * from rdb$relations;↵

Although you haven't created any tables yet, the screen will fill up with a large amount of data! This query selects all of the rows in the system table RDB$RELATIONS, where Firebird stores the metadata for tables. An “empty” database is not really empty: it contains a number of system tables and other objects. The system tables will grow as you add more user objects to your database.

To get back to the command prompt type QUIT or EXIT, as explained in the section on connecting.

Creating a database as a non-privileged user

In Firebird 3, if you try to create a database other than in embedded mode as someone who is not a Firebird admin (i.e. SYSDBA or an account with equal rights), you may be in for a surprise:

SQL>create database 'xnet://D:\data\mydb.fdb' user 'john' password 'lennon';↵
Statement failed, SQLSTATE = 28000
no permission for CREATE access to DATABASE D:\DATA\MYDB.FDB

Non-admin users must explicitly be granted the right to create databases by a Firebird admin:

SQL>grant create database to user john;↵

After that, they can create databases.

Notice that with a serverless connection, i.e. without specifying a host name or protocol before the database name (and Engine12 enabled!), Firebird won't deny any CREATE DATABASE statement. It will only fail if the client process doesn't have sufficient rights in the directory where the database is to be created.

Firebird SQL

Every database management system has its own idiosyncrasies in the ways it implements SQL. Firebird adheres to the SQL standard more rigorously than most other RDBMSes. Developers migrating from products that are less standards-compliant often wrongly suppose that Firebird is quirky, whereas many of its apparent quirks are not quirky at all.

Division of an integer by an integer

Firebird accords with the SQL standard by truncating the result (quotient) of an integer/integer calculation to the next lower integer. This can have bizarre results unless you are aware of it.

For example, this calculation is correct in SQL:

1 / 3 = 0

If you are upgrading from an RDBMS which resolves integer/integer division to a float quotient, you will need to alter any affected expressions to use a float or scaled numeric type for either dividend, divisor, or both.

For example, the calculation above could be modified thus in order to produce a non-zero result:

1.000 / 3 = 0.333

Things to know about strings

String delimiter symbol

Strings in Firebird are delimited by a pair of single quote (apostrophe) symbols: 'I am a string' (ASCII code 39, not 96). If you used earlier versions of Firebird's relative, InterBase®, you might recall that double and single quotes were interchangeable as string delimiters. Double quotes cannot be used as string delimiters in Firebird SQL statements.

Apostrophes in strings

If you need to use an apostrophe inside a Firebird string, you can “escape” the apostrophe character by preceding it with another apostrophe.

For example, this string will give an error:

'Joe's Emporium'

because the parser encounters the apostrophe and interprets the string as 'Joe' followed by some unknown keywords. To make it a legal string, double the apostrophe character:

'Joe''s Emporium'

Notice that this is TWO single quotes, not one double-quote.

Concatenation of strings

The concatenation symbol in SQL is two “pipe” symbols (ASCII 124, in a pair with no space between). In SQL, the “+” symbol is an arithmetic operator and it will cause an error if you attempt to use it for concatenating strings. The following expression prefixes a character column value with the string “Reported by: ”:

'Reported by: ' || LastName

Firebird will raise an error if the result of a string concatenation exceeds the maximum (var)char size of 32 Kb. If only the potential result – based on variable or field size – is too long you'll get a warning, but the operation will be completed successfully. (In pre-2.0 Firebird, this too would cause an error and halt execution.)

See also the section below, Expressions involving NULL, about concatenating in expressions involving NULL.

Double-quoted identifiers

Before the SQL-92 standard, it was not legal to have object names (identifiers) in a database that duplicated keywords in the language, were case-sensitive or contained spaces. SQL-92 introduced a single new standard to make any of them legal, provided that the identifiers were defined within pairs of double-quote symbols (ASCII 34) and were always referred to using double-quote delimiters.

The purpose of this “gift” was to make it easier to migrate metadata from non-standard RDBMSes to standards-compliant ones. The down-side is that, if you choose to define an identifier in double quotes, its case-sensitivity and the enforced double-quoting will remain mandatory.

Firebird does permit a slight relaxation under a very limited set of conditions. If the identifier which was defined in double-quotes:

  1. was defined as all upper-case,

  2. is not a keyword, and

  3. does not contain any spaces,

...then it can be used in SQL unquoted and case-insensitively. (But as soon as you put double-quotes around it, you must match the case again!)


Don't get too smart with this! For instance, if you have tables "TESTTABLE" and "TestTable", both defined within double-quotes, and you issue the command:

SQL>select * from TestTable; will get the records from "TESTTABLE", not "TestTable"!

Unless you have a compelling reason to define quoted identifiers, it is recommended that you avoid them. Firebird happily accepts a mix of quoted and unquoted identifiers – so there is no problem including that keyword which you inherited from a legacy database, if you need to.


Some database admin tools enforce double-quoting of all identifiers by default. Try to choose a tool which makes double-quoting optional.

Expressions involving NULL

In SQL, NULL is not a value. It is a condition, or state, of a data item, in which its value is unknown. Because it is unknown, NULL cannot behave like a value. When you try to perform arithmetic on NULL, or involve it with values in other expressions, the result of the operation will almost always be NULL. It is not zero or blank or an “empty string” and it does not behave like any of these values.

Below are some examples of the types of surprises you will get if you try to perform calculations and comparisons with NULL.

The following expressions all return NULL:

  • 1 + 2 + 3 + NULL

  • not (NULL)

  • 'Home ' || 'sweet ' || NULL

You might have expected 6 from the first expression and “Home sweet ” from the third, but as we just said, NULL is not like the number 0 or an empty string – it's far more destructive!

The following expression:

  • FirstName || ' ' || LastName

will return NULL if either FirstName or LastName is NULL. Otherwise it will nicely concatenate the two names with a space in between – even if any one of the variables is an empty string.


Think of NULL as UNKNOWN and these strange results suddenly start to make sense! If the value of Number is unknown, the outcome of '1 + 2 + 3 + Number' is also unknown (and therefore NULL). If the content of MyString is unknown, then so is 'MyString || YourString' (even if YourString is non-NULL). Etcetera.

Now let's examine some PSQL (Procedural SQL) examples with if-constructs:

  • if (a = b) then
      MyVariable = 'Equal';
      MyVariable = 'Not equal';

    After executing this code, MyVariable will be 'Not equal' if both a and b are NULL. The reason is that 'a = b' yields NULL if at least one of them is NULL. If the test expression of an “if” statement is NULL, it behaves like false: the 'then' block is skipped, and the 'else' block executed.


    Although the expression may behave like false in this case, it's still NULL. If you try to invert it using not(), what you get is another NULL – not “true”.

  • if (a <> b) then
      MyVariable = 'Not equal';
      MyVariable = 'Equal';

    Here, MyVariable will be 'Equal' if a is NULL and b isn't, or vice versa. The explanation is analogous to that of the previous example.

The DISTINCT keyword comes to the rescue!

Firebird 2 and above implement a new use of the DISTINCT keyword allowing you to perform (in)equality tests that take NULL into account. The semantics are as follows:

  • Two expressions are DISTINCT if they have different values or if one is NULL and the other isn't;

  • They are NOT DISTINCT if they have the same value or if they are both NULL.

Notice that if neither operand is NULL, DISTINCT works exactly like the “<>” operator, and NOT DISTINCT like the “=” operator.

DISTINCT and NOT DISTINCT always return true or false, never NULL.

Using DISTINCT, you can rewrite the first PSQL example as follows:

if (a is not distinct from b) then
  MyVariable = 'Equal';
  MyVariable = 'Not equal';

And the second as:

if (a is distinct from b) then
  MyVariable = 'Not equal';
  MyVariable = 'Equal';

These versions will give you the results that a normal (i.e. not SQL-brainwashed) human being would expect, whether there are NULLs involved or not.

More about NULLs

A lot more information about NULL behaviour can be found in the Firebird Null Guide, at these locations:

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