Working with databases

Connecting to the sample database
Creating a database using isql
Firebird SQL

Connecting to the sample database

In the examples subdirectory of your Firebird installation is a sample database named employee.fdb. You can use this database to “try your wings”.

Server name and path

If you move the sample database, be sure you move it to 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.

There are two elements to a TCP/IP connection string: the server name and the disk/filesystem path. Its format is as follows:

For a Linux server:

servername:/filesystem-path/database-file

Example on a Linux or other Posix server named serverxyz:

serverxyz:/opt/interbase/examples/employee.fdb
For a Windows server:

servername:DriveLetter:\filesystem-path\database-file

Windows example:

serverxyz:C:\Program Files\Firebird\examples\employee.fdb

The CONNECT statement

Connecting to a Firebird database requires the user to authenticate using a user name and a valid password. Any user other than SYSDBA, root (on Posix systems), or Administrator (on Windows systems, if Firebird runs as this user) needs also to have permissions to objects inside a database. For simplicity here, we will look at authenticating as SYSDBA using the password masterkey.

Using isql

There are several different ways to connect to a database using isql. One way is to start isql in its interactive shell. Go to the bin subdirectory of your Firebird installation and, at that prompt, type the command isql (on Linux: ./isql) [↵ means “hit Enter”]:

C:\Program Files\Firebird\Firebird_1_5\bin>isql↵
Use CONNECT or CREATE DATABASE to specify a database
SQL>CONNECT "C:\Program Files\Firebird\Firebird_1_5\examples\employee.fdb"↵
CON>user 'SYSDBA' password 'masterkey';↵

Important

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 spread long statements over multiple lines. If you hit Enter after your statement and you've forgotten the semicolon, just type it on the empty line after the CON> prompt and press Enter again.
If you run 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, connect to localhost:/<path>. Then the server process (with Firebird 1.5 usually running as 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.
If you run Classic Server on Windows, you must specify a hostname (which may be localhost) plus a full path, or the connection will fail.

Note

Although single quote symbols are the “norm” for delimiting strings in Firebird, double quote symbols were used with the database path string in the above example. This is sometimes necessary with some of the command-line utilities where the path string contains spaces. Single quotes should work for paths that do not contain spaces.

The quotes around “SYSDBA” and “masterkey” are optional, by the way. Database paths without spaces also don't need to be quoted.

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

DATABASE "C:\Program Files\Firebird\Firebird_1_5\examples\employee.fdb",
User: sysdba
SQL>

You can now continue to play about with the employee.fdb database. The characters isql stand for interactive SQL [utility]. You can use it for querying data, getting information about the metadata, creating database objects, running data definition scripts and much more.

To get back to the command prompt type

SQL>QUIT;↵

For more information about isql, see Using Firebird, Chapter 10: Interactive SQL Utility (isql).

Using a GUI client

GUI client tools usually take charge of composing the CONNECT string for you, using server, path, user name and password information that you type into prompting fields. Use the elements as described in the preceding topic.

Note

It is quite common for such tools to expect the entire server + path as a single string
Remember that file names and commands on Linux and other Posix command shells are case-sensitive

Creating a database using isql

There is more than one way to create a database using 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. There is a complete chapter in the Using Firebird manual discussing this topic.

Starting isql

To create a database interactively using the isql command shell, get to a command prompt in Firebird's bin subdirectory and type isql (Windows) or ./isql (Linux):

C:\Program Files\Firebird\Firebird_1_5\bin>isql↵
Use CONNECT or CREATE DATABASE to specify a database

The CREATE DATABASE statement

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';↵

Important

In the CREATE DATABASE statement the quotes around path string, username, and password are mandatory. This is different from the CONNECT statement.
If you run 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 (with Firebird 1.5 usually running as firebird) will create and own the file.
If you run Classic Server on Windows, you must specify a hostname (which may be localhost) plus a full path, or the creation will fail.

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.

To verify that there really is a database there, type in this query:

SQL>SELECT * FROM RDB$RELATIONS;↵

The screen will fill up with a large amount of data! This query selects all of the rows in the system table where Firebird stores the metadata for tables. An “empty” database is not empty – it contains a database which will become populated with metadata as you begin creating objects in your database.

To get back to the command prompt type

SQL>QUIT;↵

For more information about isql, see Using Firebird, Chapter 10: Interactive SQL Utility (isql).

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 any other RDBMS except possibly its “cousin”, InterBase®. 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 a 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 this 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 characters “Reported by: ”:

'Reported by: ' || LastName

Take care with concatenations. Be aware that Firebird will raise an error if your expression attempts to concatenate two or more char or varchar columns whose potential combined lengths would exceed the maximum length limit for a char or a varchar (32 Kb).

See also the note 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 RDBMSs 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!)

Warning

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.

Warning

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.

So – here are some examples of the types of surprises you will get if you try to perform calculations and comparisons with NULL:

1 + 2 + 3 + NULL = NULL
not (NULL) = NULL
'Home ' || 'sweet ' || NULL = NULL
```
if (a = b) then
  MyVariable = 'Equal';
else
  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.

Warning

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';
else
  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.
```
FirstName || ' ' || LastName
```
will return NULL if either FirstName or LastName is NULL.

Tip

Think of NULL as UNKNOWN and all 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.

More about `NULL`s

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