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Internal functions and directives

Internal functions

The following built-in functions return NULL if at least one argument is NULL:

• CAST()
• EXTRACT()
• GEN_ID()
• SUBSTRING()
• UPPER()
• LOWER()
• BIT_LENGTH()
• CHAR[ACTER]_LENGTH()
• OCTET_LENGTH()
• TRIM()

Notes • In 1.0.0, EXTRACT from a NULL date would crash the server. Fixed in 1.0.2. • If the first argument to GEN_ID is a valid generator name and the second argument is NULL, the named generator keeps its current value. • In versions up to and including 2.0, SUBSTRING results are sometimes returned as "false emptystrings". These strings are in fact NULL, but are described by the server as non-nullable. Therefore, most clients show them as empty strings. See the bugs list for a detailed description.

FIRST, SKIP and ROWS

The following two directives crash a Firebird 1.5.n or lower server if given a NULL argument. In Firebird 2, they treat NULL as the value 0:

• FIRST
• SKIP

This new Firebird 2 directive returns an empty set if any argument is NULL:

• ROWS

Side note: ROWS complies with the SQL standard. In new code, use ROWS, not FIRST and SKIP.

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