I_S tables don't tell that the stored function is AGGREGATE

INFORMATION_SCHEMA.ROUTINES does not tell whether a particular storage function is aggregate or not.

How can we show it? Let's also think how it can be extended to work for window functions later. Options are:

new ROUTINE_TYPE

The standard defines it as

ROUTINE_TYPE INFORMATION_SCHEMA.CHARACTER_DATA NOT NULL

    CHECK ( ROUTINE_TYPE IN ( 'PROCEDURE', 'FUNCTION', 'INSTANCE METHOD', 'STATIC METHOD', 'CONSTRUCTOR METHOD' ) ),

we can add 'AGGREGATE FUNCTION' to the list. And 'WINDOW FUNCTION' later.

new field IS_AGGREGATE

the standard ROUTINE table has many fields like

IS_DETERMINISTIC INFORMATION_SCHEMA.YES_OR_NO,

IS_NULL_CALL INFORMATION_SCHEMA.YES_OR_NO,

IS_USER_DEFINED_CAST INFORMATION_SCHEMA.YES_OR_NO,

IS_IMPLICITLY_INVOCABLE INFORMATION_SCHEMA.YES_OR_NO,

so IS_AGGREGATE would be quite in line with that. Window functions, though, will need yet another column.

new field FUNCTION_KIND (or something like that)

the standard ROUTINE table has numerous ENUM-like fields (e.g. ROUTINE_TYPE). Another ENUM-like field with values ENUM('NORMAL', 'AGGREGATE') will not look too strange. 'WINDOW' can later be added easily.