9.18. UPDATE Statement
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) ;