SQL functions built into Oracle Database can indeed perform tasks such as displaying a date in a nondefault format, finding the number of characters in an expression, and substituting a character string in a text expression with a specified string. These tasks are handled using various built-in functions like TO_CHAR for date formatting, LENGTH for finding the number of characters, and REPLACE for substituting strings. Combining more than two columns or expressions into a single column in the output is not typically done using a single function, as the CONCAT function in Oracle is limited to two parameters, though it can be achieved using the concatenation operator ||.