Conditional expression functions

Function	Support	Notes
`COALESCE`	Supported
`GREATEST`	Supported
`IFF`	Supported
`IFNULL`	Supported
`LEAST`	Supported
`NOT`	Supported
`NULLIFZERO`	Supported
`NULLIF`	Supported
`NVL2`	Supported
`NVL`	Supported
`ZEROIFNULL`	Supported
`DECODE`	With limitations	Available for some argument types only.
`BOOLAND`, `BOOLNOT`, `BOOLOR`, `BOOLXOR`, `EQUAL_NULL`, `GREATEST_IGNORE_NULLS`, `LEAST_IGNORE_NULLS`, `REGR_VALX`, `REGR_VALY`	Not supported