ODBC and JDBC Guide

Chapter 7 | Supported standards 38
The following example is not valid because the data types of the column expressions are different
(SALARY from EMP has a different data type than LAST_NAME from RAISES). This example has
the same number of column expressions in each SELECT statement, but the expressions are not
in the same order by data type.
SELECT last_name, salary FROM emp UNION SELECT salary, last_name FROM raises
ORDER BY clause
The ORDER BY clause indicates how the records are to be sorted. The format is:
ORDER BY {sort_expression [DESC | ASC]}, ...
sort_expression can be field names, expressions, or the positional number of the column
expression to use. The default is to perform an ascending (ASC) sort.
For example, to sort by last_name then by first_name, you could use either of the following
SELECT statements:
SELECT emp_id, last_name, first_name FROM emp ORDER BY last_name, first_name
or
SELECT emp_id, last_name, first_name FROM emp ORDER BY 2,3
In the second example, last_name is the second column expression following SELECT, so ORDER
BY 2 sorts by
last_name.
FOR UPDATE clause
The FOR UPDATE clause locks records for Positioned Updates or Positioned Deletes via SQL
cursors. The format is:
FOR UPDATE [OF column_expressions]
column_expressions is a list of field names in the database table that you intend to update,
separated by a comma.
column_expressions is optional, and is ignored.
Example
The following example returns all records in the employee database that have a SALARY field
value of more than $20,000. When each record is fetched, it is locked. If the record is updated or
deleted, the lock is held until you commit the change. Otherwise, the lock is released when you
fetch the next record.
SELECT * FROM emp WHERE salary > 20000
FOR UPDATE OF last_name, first_name, salary