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:

  • The __raw__ column of a flex table
  • Data returned from a map function such as MAPLOOKUP
  • Other database content
virtual-column-name

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)

See Also