Existing rows (or records) are changed in the database using the UPDATE statement.

NULL values can be utilized using the NULL keyword without any quotes. Since NULL is a special keyword you do not need to enclose it in single quotes, doing so will cause it be read as a string-literal.

The update statement is made up by selecting the table to update, the search condition that identifies which rows you want to update, and the column=value of each column you wish to change.

Example 9.30. Basic Update Statement

A table can be updated using:

update demo.dba.employees e
  set username = 'thing'
  where email_address = 'thing@thingdom.com'
  ;

Example 9.31. Update from Select

It is possible to update one table based on a select from another table. Ensure that the selection is properly conditioned to update.

update demo.dba.employees e
        set username = (select U_NAME from DB.DBA.SYS_USERS u where u.U_EMAIL = e.email_address)
        ;