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Internal functions and directives

Internal functions
FIRST, SKIP and ROWS

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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