ODBC and JDBC Guide

Chapter 7 | Supported standards 42
The SELECT statement is a query that returns values for each column_name value specified in the
column name list. Using a SELECT statement instead of a list of value expressions lets you select
a set of rows from one table and insert it into another table using a single INSERT statement.
Here's an example of an INSERT statement that uses a SELECT statement:
INSERT INTO emp1 (first_name, last_name, emp_id, dept, salary)
SELECT first_name, last_name, emp_id, dept, salary from emp
WHERE dept = ‘D050’
In this type of INSERT statement, the number of columns to be inserted must match the number
of columns in the SELECT statement. The list of columns to be inserted must correspond to the
columns in the SELECT statement just as it would to a list of value expressions in the other type
of INSERT statement. For example, the first column inserted corresponds to the first column
selected; the second inserted to the second, and so on.
The size and data type of these corresponding columns must be compatible. Each column in the
SELECT list should have a data type that the ODBC or JDBC client driver accepts on a regular
INSERT/UPDATE of the corresponding column in the INSERT list. Values are truncated when the
size of the value in the SELECT list column is greater than the size of the corresponding INSERT
list column.
The SELECT statement is evaluated before any values are inserted.
UPDATE statement
Use the UPDATE statement to change records in a database table. The format of the UPDATE
statement is:
UPDATE table_name SET column_name = expr, ... [ WHERE { conditions } ]
column_name is the name of a column whose value is to be changed. Several columns can be
changed in one statement.
expr is the new value for the column.
Usually the expressions are constant values for the columns (but they can also be a subquery).
You must enclose character string values in pairs of single quotation marks ('). To include a single
quotation mark in a character string value enclosed by single quotation marks, use two single
quotation marks together (for example, 'Don''t').
Subqueries must be enclosed in parentheses.
The WHERE clause is any valid clause. It determines which records are updated.
Examples
An example of an UPDATE statement on the Employee table is:
UPDATE emp SET salary=32000, exempt=1 WHERE emp_id = 'E10001'
The UPDATE statement changes every record that meets the conditions in the WHERE clause. In
this case the salary and exempt status are changed for all employees having the employee ID
E10001. Because employee IDs are unique in the Employee table, only one record is updated.
Here's an example using a subquery:
UPDATE emp SET salary = (SELECT avg(salary) from emp) WHERE emp_id = 'E10001'