For a compound WHERE clause, ABL builds a logic tree and evaluates index usage on either side of the OR. In general, if all selection criteria on both sides of the OR include matches—equality, range, or sort—on successive, leading components of two non-unique indexes, ABL uses both indexes:

Sample WHERE clause Indexes used 
WHERE Customer.Comments CONTAINS "to*" 
   OR Customer.Name = "Carlin"
 Comments

Name

 
WHERE Name > "Beaudette"
   OR Country > "Zambia"
 Name

Country-Post

In addition, if one side of the OR includes a CONTAINS clause (that is, it uses a word index), ABL uses the word index and then a second index to satisfy the other side of the OR: 

WHERE Comments CONTAINS "credit"
   OR Postal-Code > "01000"
 Comments

Cust-Num

In this example, the right side of the OR includes a range match, but Postal-Code is the second component of the County-Post index, so the match is not active. ABL uses the primary index to satisfy this piece of the query and, as always, uses the word index to satisfy a CONTAINS clause as shown in this example:

WHERE Comments CONTAINS "credit"
   OR Postal-Code < "01000" 
   BY Sales-Rep
 Comments

Sales-Rep

If the selection criteria do not support multiple index usage, see the General rules for choosing a single index.

Note: If any expression on either side of the OR does not use an index or all its components, ABL must scan all records using the primary index.