*** DRAFT ***

SQLite C Interface

Function Flags

#define SQLITE_DETERMINISTIC    0x000000800
#define SQLITE_DIRECTONLY       0x000080000
#define SQLITE_SUBTYPE          0x000100000
#define SQLITE_INNOCUOUS        0x000200000
#define SQLITE_RESULT_SUBTYPE   0x001000000

These constants may be ORed together with the preferred text encoding as the fourth argument to sqlite3_create_function(), sqlite3_create_function16(), or sqlite3_create_function_v2().

The SQLITE_DETERMINISTIC flag means that the new function always gives the same output when the input parameters are the same. The abs() function is deterministic, for example, but randomblob() is not. Functions must be deterministic in order to be used in certain contexts such as with the WHERE clause of partial indexes or in generated columns. SQLite might also optimize deterministic functions by factoring them out of inner loops.

The SQLITE_DIRECTONLY flag means that the function may only be invoked from top-level SQL, and cannot be used in VIEWs or TRIGGERs nor in schema structures such as CHECK constraints, DEFAULT clauses, expression indexes, partial indexes, or generated columns.

The SQLITE_DIRECTONLY flag is recommended for any application-defined SQL function that has side-effects or that could potentially leak sensitive information. This will prevent attacks in which an application is tricked into using a database file that has had its schema surreptitiously modified to invoke the application-defined function in ways that are harmful.

Some people say it is good practice to set SQLITE_DIRECTONLY on all application-defined SQL functions, regardless of whether or not they are security sensitive, as doing so prevents those functions from being used inside of the database schema, and thus ensures that the database can be inspected and modified using generic tools (such as the CLI) that do not have access to the application-defined functions.

The SQLITE_INNOCUOUS flag means that the function is unlikely to cause problems even if misused. An innocuous function should have no side effects and should not depend on any values other than its input parameters. The abs() function is an example of an innocuous function. The load_extension() SQL function is not innocuous because of its side effects.

SQLITE_INNOCUOUS is similar to SQLITE_DETERMINISTIC, but is not exactly the same. The random() function is an example of a function that is innocuous but not deterministic.

Some heightened security settings (SQLITE_DBCONFIG_TRUSTED_SCHEMA and PRAGMA trusted_schema=OFF) disable the use of SQL functions inside views and triggers and in schema structures such as CHECK constraints, DEFAULT clauses, expression indexes, partial indexes, and generated columns unless the function is tagged with SQLITE_INNOCUOUS. Most built-in functions are innocuous. Developers are advised to avoid using the SQLITE_INNOCUOUS flag for application-defined functions unless the function has been carefully audited and found to be free of potentially security-adverse side-effects and information-leaks.

The SQLITE_SUBTYPE flag indicates to SQLite that a function might call sqlite3_value_subtype() to inspect the sub-types of its arguments. This flag instructs SQLite to omit some corner-case optimizations that might disrupt the operation of the sqlite3_value_subtype() function, causing it to return zero rather than the correct subtype(). SQL functions that invokes sqlite3_value_subtype() should have this property. If the SQLITE_SUBTYPE property is omitted, then the return value from sqlite3_value_subtype() might sometimes be zero even though a non-zero subtype was specified by the function argument expression.

The SQLITE_RESULT_SUBTYPE flag indicates to SQLite that a function might call sqlite3_result_subtype() to cause a sub-type to be associated with its result. Every function that invokes sqlite3_result_subtype() should have this property. If it does not, then the call to sqlite3_result_subtype() might become a no-op if the function is used as term in an expression index. On the other hand, SQL functions that never invoke sqlite3_result_subtype() should avoid setting this property, as the purpose of this property is to disable certain optimizations that are incompatible with subtypes.

See also lists of Objects, Constants, and Functions.