Difference between revisions of "Portable SQL/Common/DBMS Differences"
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Revision as of 16:40, 4 September 2006
Contents
Differences between implementations
Identifiers
Parts of this table are originally from "Building Truly Portable Database Applications in PHP": Column Name Case
| Database | Length | Allowed | Case | Notes |
|---|---|---|---|---|
| Firebird | 31 | L,D (?) | upper | case preserved with double quotes (") |
| MySQL | 64 | L,NL,D,_,$ | preserved | |
| Oracle | 30 | L,NL,D,_,$,# | upper | Info, max. DB name length is 8 |
| PostgreSQL | 63 | L,NL,D,_,$ | lower | case preserved with double quotes (") |
| SQL Server | 127 | L,NL,D,_,$,@,# | preserved | Info |
| SQLite | 255 | L,NL,D,_ | preserved | |
| Sybase ASE | 131 | L,NL,D,_,$,@,# | preserved | max. DB and Cursor name length is 28 |
Explanation of allowed symbols:
- L = Letters
- NL = Non-latin letters
- D = Digits
In general, all identifiers must start with a letter or non-latin letter; digits and other symbols as first characters are often not allowed or change their meaning.
Since OpenDBX 1.1.4 the use of double quotes (") for identifiers (table and column names) is suggested. This complies to ANSI standards and is the only way to use reserved words and prevent clashes in the future if language constructs are extended by the database vendors.
NULL in column definition
This table is originally from "Building Truly Portable Database Applications in PHP": NULL
| Database | Default value | Definition allowed | Notes |
|---|---|---|---|
| Firebird | NULL | no | |
| MySQL | NULL | yes | |
| Oracle | NULL | yes | Empty strings considered NULL |
| PostgreSQL | NULL | yes | |
| SQL Server | NOT NULL | yes | |
| SQLite | NULL | yes | |
| Sybase ASE | NOT NULL | yes |
The "Definition allowed" column indicates if specifying NULL in table column definitions is allowed for CREATE TABLE statements - NOT NULL is always allowed. If "yes", the following statement doesn't generate an error:
CREATE TABLE mytable ( id INTEGER NULL )
Quotes and numeric values
MS SQL Server and Sybase ASE doesn't allow single quotes (') around numeric values (integer and floating point values), for example
INSERT INTO table (floatval,string) VALUES ('-3.14','some text')
generates an error when using these servers. They only accept
INSERT INTO table (floatval,string) VALUES (-3.14,'some text')
This gets tricky if the values are supplied by a user. You must validate the input to be sure it is a numeric value and you can't use the escape() function. Otherwise, if you don't look at the input, your application will be vulnerable to SQL injection and you will be in deep trouble.
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