. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5.1.2. With a NULL test expression. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . where A + B + C is not null delete from Phonebook where PhoneNum is null Do not use “… = NULL” to test for nullness. This syntax is illegal in Firebird versions up to 1.5.n, and gives the wrong result ProcessThis(88, 'Apes', Null) Remember: • You cannot — and should not — use the comparison operator ‘=’ to test if something is NULL… • …but you can — and often must — use the assignment operator ‘=’ to set something

host IP address and database path. For example: connect '[2014:1234::5]:test'; connect '[2014:1234::5]/3049:/srv/firebird/test.fdb';  For consistency, square brackets can be optionally used around database using the alias rather than a full path: $ /opt/firebird/bin/isql my_employee Database: test, User: sysdba SQL> Alternatively, a remote connection would be made as follows, specifying the server MON$DATABASE_NAME from mon$database; MON$DATABASE_NAME ================================= /data/databases/firebird/test.fdb Chapter 8. Connecting To A Database 17 Chapter 9. Creating A Database To create a database

базы данных. Синтаксис: DROP DOMAIN name; Пример: DROP DOMAIN Test_Domain; См. также: DROP DOMAIN. 58 Глава 3 Общие элементы языка В этой CASE Синтаксис: CASE <test-expr> WHEN THEN [WHEN THEN ...] [ELSE ] END При использовании этого варианта <test-expr> сравнивается с ветвь ELSE отсутствует, возвращается значение NULL. Совпадение эквивалентно оператору «=», т.е. если <test-expr> имеет значение NULL, то он не соответствует ни одному из , даже тем, которые имеют значение

compare): set *sqldata to the supplied value and *sqlind to 0 (for NOT NULL) Second parameter (NULL test): set sqldata to null (null pointer, not SQL NULL) and *sqlind to 0 (for NOT NULL) User has left DROP DOMAIN name  Any user connected to the database can delete a domain. Example DROP DOMAIN Test_Domain See also DROP DOMAIN in the Data Definition Language (DDL) section. Chapter 3. Data Types expressions that are used to extract and operate on assertions about data and the predicates that test the truth of those assertions. 4.1. Expressions SQL expressions provide formal methods for evaluating

2 3 2. Test for TRUE value SELECT * FROM TBOOL WHERE BVAL; ID BVAL ============ ======= 1 3. Test for FALSE value SELECT * FROM TBOOL WHERE WHERE BVAL IS FALSE; ID BVAL ============ ======= 2 4. Test for UNKNOWN value SELECT * FROM TBOOL WHERE BVAL IS UNKNOWN; ID BVAL ============ ======= compare): set *sqldata to the supplied value and *sqlind to 0 (for NOT NULL) Second parameter (NULL test): set sqldata to null (null pointer, not SQL NULL) and *sqlind to 0 (for NOT NULL) User has left

même résultat que l'exemple précédent, n'est ce pas? Après tout, nous avons inversé l'expression de test et interverti les clauses then et else. Et de fait, tant qu'aucune variable est NULL, les deux codes proposé que pour insister sur le fait que not(NULL) est NULL. Donc, dans les situations où l'expression testée est NULL, not() n'inverse pas le résultat . Tester si quelque chose est NULL Puisque NULL peut quelque chose est NULL avant de l'utiliser dans une expression. La plupart du temps, on pense que le test le plus indiqué serait if (A = NULL) then... et de fait certains systèmes de gestion de base de

Простой CASE Синтаксис: CASE <test-expr> WHEN THEN result [WHEN THEN result ...] [ELSE defaultresult] END При использовании этого варианта <test-expr> сравнивается с 1, отсутствует, возвращается значение NULL. Совпадение эквивалентно оператору «=», т.е. если <test-expr> имеет значение NULL, то он не соответствует ни одному из , даже тем, которые имеют значение синтаксисом начиная с Firebird 2.0. Синтаксис: CREATE SEQUENCE sequence-name Пример: CREATE SEQUENCE SEQ_TEST Поскольку по своему функционалу последовательности и генераторы аналогичны (Примечание переводчика:

they all should be — you are strongly advised to take your backup files and use them to create a test restore of a database either on the same server or even better, on a different one. Only by doing restore.test At this point, the restore has worked and has overwritten the previous database known as employee.restore.test. The actual location of the database for the database employee.restore.test is is defined in the aliases.conf file in /opt/firebird on the server. In this test, it resolves to /opt/firebird/databases/employee.restore.fdb. For further proof of reliability, the application

deploy to user sites will be determined by comparing the per- formance of one with another in your test lab. You don't have to do anything to a database in order to make it work under a different server well. Winsock2 Firebird requires WinSock2. All Win32 platforms should have this, except for Win95. A test for the Winsock2 library is made during install. If it is not found the install will fail. To find firebird user, run the following script: $cd /opt/firebird/bin $./createAliasDB.sh test.fdb /var/firebird/test.fdb (Usage is: createAliasDB.sh ) 3. As an alternative

2 3 2. Test auf Wert TRUE SELECT * FROM TBOOL WHERE BVAL; ID BVAL ============ ======= 1 3. Test auf Wert FALSE SELECT * FROM TBOOL WHERE WHERE BVAL IS FALSE; ID BVAL ============ ======= 2 4. Test auf Wert UNKNOWN SELECT * FROM TBOOL WHERE BVAL IS UNKNOWN; ID BVAL ============ ======= Chapter setze *sqldata auf den angegebenen Wert und *sqlind auf 0 (für NOT NULL) Zweiter Parameter (NULL Test): setze sqldata auf null (Nullzeiger, nicht SQL NULL) und *sqlind auf 0 (für NOT NULL) Der Benutzer