cf(uid)

Function name Description
cf(uid) Returns a relation which lists all custom fields for the given UID.
Parameter name Description
uid The UID (account or subscription ID) for which you wish to retrieve the custom fields.
This function returns all custom fields for a given UID.
Note: Note that cf(uid) returns a relation - that is, it works like an SQL table rather than an SQL column. The cf(uid) function can therefore be used anywhere a table might be used. This also means that you will see strange results if you try to use cf(uid) as a column in a query.
To list all of the custom fields on an account:
SELECT * FROM cf(uid('2142420815')) ORDER BY custom_field;
    custom_field   |      value
 ------------------+------------------
 usn               | 2142420815
 companyName       |
 contactNameTitle  | Mr
 contactNameFamily | Keating
 contactNameGiven  | Paul
 creationDate      | 2012-05-07
Because cf(uid) is a relation, you can order the results any way you like:
SELECT * FROM cf(uid('2142420815')) ORDER BY custom_field;
       custom_field         |           value
 ---------------------------+---------------------------
 billingAddressCountry      | Australia
 billingAddressPostcode     | 3546
 billingAddressState        | VIC
 billingAddressStreetName   | First
 billingAddressStreetNumber | 33
You can join the results with any other table, including the custom_fields table:
SELECT name, value FROM cf(uid('2142420815')) JOIN custom_fields ON (custom_fields.code = custom_field);
          name         |         value
 ----------------------+----------------------
 Billing Country       | Australia
 Billing Postcode      | 3546
 Billing State         | VIC
 Billing Street Name   | First
 Billing Street Number | 33
 Billing Street Type   | ST
 Billing Suburb        | Wellville