Selecting Data

Example 1. Where Clause Pushdown

In this example, the SQL query generated by DataDirect XQuery® returns only the rows that are actually needed for the XQuery.

XQuery (with Where clause)

for $h in collection('HOLDINGS')/HOLDINGS
where $h/SHARES < 10000
return $h/USERID  

XQuery (with predicate)

for $h in collection('HOLDINGS')/HOLDINGS[SHARES < 10000]
return $h/USERID

Generated SQL (for both forms of the XQuery)

SELECT ALL
  nrm4."USERID" AS RACOL1
FROM
  "PEPPINO"."HOLDINGS" nrm4
WHERE
  nrm4."SHARES" < 10000

Example 2. Column Pushdown

The SQL query generated by DataDirect XQuery® retrieves only the columns that are actually needed for the XQuery.

XQuery

for $u in collection('USERS')/USERS
return <user>{$u/FIRSTNAME,$u/LASTNAME}</user>

Generated SQL

SELECT ALL
  nrm5."FIRSTNAME" AS RACOL1,
  nrm5."LASTNAME" AS RACOL2
FROM
  "PEPPINO"."USERS" nrm5