|Firebird Documentation Index → Firebird 2.5 Quick Start → Working with databases|
In this part of the manual you will learn:
how to connect to an existing database,
how to create a database,
and some things you should know about Firebird SQL.
In as much as remote connections are involved, we will use the recommended TCP/IP protocol.
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.
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
them 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:
If your local 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
Global\FIREBIRD in the configuration file
firebird.conf (don't forget to uncomment the parameter and restart
IpcName doesn't help and you don't get the local
protocol enabled, you can always work around the problem by putting
localhost:” before your database paths or aliases, thus
turning them into TCP/IP connection strings (discussed below).
A TCP/IP connection string consists of:
a server name or IP address
a colon (“
either the absolute path + filename on the server machine, or an alias defined on the server machine.
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.
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) filesystems will not work. The same rule applies to any databases that you create or use.
Connecting to a Firebird database requires the user to authenticate with a user name and
a valid password. In order to work with objects inside the database – such as tables, views,
etc. – you also 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 SYSDBA. In the example database
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 relative paths. 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.
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
bin subdirectory of your Firebird installation and type
isql (Windows) or ./isql (Linux) at the command
[In the following examples, ↵ means “hit Enter”]
C:\Program Files\Firebird\Firebird_2_5\bin>isql↵ Use CONNECT or CREATE DATABASE to specify a database SQL>CONNECT ..\examples\empbuild\employee.fdb 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
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
If you run a (Super)Classic Server on Linux, a fast, direct local connection is
attempted if the database path does not start with a hostname. This may fail if your
Linux login doesn't have sufficient access rights to the database file. In that case,
the server process (usually running as user
firebird) will open the file. On the other hand,
network-style connections may fail if a user created the database in Classic local
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.
At this point, isql will inform you that you are connected:
Database: ..\examples\empbuild\employee.fdb, User: sysdba SQL>
You can now continue to play about with the
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 command prompt, type:
You can also type
EXIT instead of
difference being that
EXIT will first commit any open transactions,
making your modifications permanent.
GUI client tools usually 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. Use the elements as described in the preceding topic.
It is 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-ish” platforms are case-sensitive.
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.
To create a database interactively using the isql command
shell, get to a command prompt in Firebird's
subdirectory and type isql (Windows) or ./isql
[In the following examples, ↵ means “hit Enter”]
C:\Program Files\Firebird\Firebird_2_5\bin>isql↵ 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
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, username and password. This is different from the CONNECT statement.
If you run a (Super)Classic Server on Linux and you don't start the database
path with a hostname, creation of the database file is attempted with your Linux 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: to the path, the server process (usually
running as user
firebird) 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
EXIT, as explained in the section on connecting.
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.
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
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.
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:
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:
Notice that this is TWO single quotes, not one double-quote.
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
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:
was defined as all upper-case,
is not a keyword, and
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;
...you will get the records from "TESTTABLE", not "TestTable"!
Unless you have a compelling reason to define quoted identifiers, it is usually 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.
NULL is not a value. It is a condition, or
state, of a data item, in which its value is unknown. Because it is
NULL cannot behave like a value. When you try to perform
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
Below are some examples of the types of surprises you will get if you try to perform
calculations and comparisons with
The following expressions all return
1 + 2 + 3 +
'Home ' || 'sweet ' ||
You might have expected 6 from the first expression and “
” 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
NULL if either
NULL. Otherwise it will nicely
concatenate the two names with a space in between – even if any one of the variables is an
UNKNOWN and these strange
results suddenly start to make sense! If the value of
unknown, the outcome of '
1 + 2 + 3 + Number' is also unknown (and
NULL). If the content of
unknown, then so is '
MyString || YourString' (even if
YourString is non-
Now let's examine some PSQL (Procedural SQL) examples with
if (a = b) then MyVariable = 'Equal'; else MyVariable = 'Not equal';
After executing this code,
MyVariable will be
equal' if both
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
then' block is skipped, and the '
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 “
if (a <> b) then MyVariable = 'Not equal'; else MyVariable = 'Equal';
MyVariable will be
b isn't, or
vice versa. The explanation is analogous to that of the previous example.
Firebird 2 and above implement a new use of the DISTINCT
keyword allowing you to perform (in)equality tests that take
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
Notice that if neither operand is
DISTINCT works exactly like the
<>” operator, and NOT DISTINCT
like the “
DISTINCT and NOT DISTINCT always return
Using DISTINCT, you can rewrite the first PSQL example as follows:
if (a is not distinct from b) then MyVariable = 'Equal'; else MyVariable = 'Not equal';
And the second as:
if (a is distinct from b) then MyVariable = 'Not equal'; else 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
A lot more information about
NULL behaviour can be found in the
Firebird Null Guide, at these locations:
|Firebird Documentation Index → Firebird 2.5 Quick Start → Working with databases|