MAPCONTAINSKEY
Determines whether a VMap contains a virtual column (key). This scalar function returns true (t
), if the virtual column exists, or false (f
) if it does not. Determining that a key exists before calling maplookup()
lets you distinguish between NULL returns. The maplookup()
function uses for both a non-existent key and an existing key with a NULL value.
Syntax
MAPCONTAINSKEY(VMap_data, 'virtual_column_name')
Arguments
VMap_data |
Any VMap data. The VMap can exist as:
|
virtual_column_name |
The name of the key to check. |
Examples
This example shows how to use the mapcontainskey()
functions with maplookup()
. View the results returned from both functions. Check whether the empty fields that maplookup()
returns indicate a NULL
value for the row (t) or no value (f
):
You can use mapcontainskey( ) to determine that a key exists before calling maplookup(). The maplookup() function uses both NULL returns and existing keys with NULL values to indicate a non-existent key.
=> SELECT MAPLOOKUP(__raw__, 'user.location'), MAPCONTAINSKEY(__raw__, 'user.location') FROM darkdata ORDER BY 1; maplookup | mapcontainskey -----------+---------------- | t | t | t | t Chile | t Narnia | t Uptown.. | t chicago | t | f | f | f | f
(12 rows)