问题：

[多选] Which four statements correctly describe functions that are available in SQL? （）

A . INSTR returns the numeric position of a named character.
B . NVL2 returns the first non-null expression in the expression list.
C . TRUNCATE rounds the column, expression, or value to n decimal places.
D . DECODE translates an expression after comparing it to each search value.
E . TRIM trims the heading or trailing characters (or both) from a character string.
F . NVL compares two expressions and returns null if they are equal, or the first expression if they are not equal.
G . NULLIF compares two expressions and returns null if they are equal, or the first expression if they are not equal.