flex-keys-columns.md

Column Description
KEY_NAME The name of the virtual column (key). Keys larger than 65,000 bytes are truncated.
FREQUENCY The number of times the key occurs in the VMap.
DATA_TYPE_GUESS Estimate of the data type for the key based on the non-null values found in the VMap. The function determines the type of each non-string value, depending on the length of the key, and whether the key includes nested maps. If the EnableBetterFlexTypeGuessing configuration parameter is 0 (OFF), this function instead treats all flex table keys as string types ([LONG] VARCHAR or [LONG] VARBINARY).