SQL Update is a command or updating a data record. SQL Update query is part of the SQL standard that is implemented by all product vendors. Thus, the concept applies uniformly across all RDBMS products. Typically, in an RDBMS based database, data is organized as rows and columns. Each row of data has fields in columns that are related. One row of data is called a record. SQL Update is a means of updating a field within a record in the database. The syntax of SQL Update command provides for specifying the particular piece of data into a database table.
The following is the syntax for the SQL Update command. The words in capitals are the keywords that must be used as is. The text strings within quote marks in the syntax of SQL Update query indicated need to be filled by actual parameter values for pinpointing the specific items to be updated.
UPDATE [table name]
SET [column name1]= ‘column value1′
WHERE [a particular column name]=’existing value of the column’
This above syntax of SQL Update specifies a specific table name on which data updates are to be made. The SET keyword lets the user specify the new values to be created in the given fields/columns of the table. The WHERE keyword specifies the existing value of a keyword so that the particular record can be pinpointed. In the absence of the WHERE keyword in the SQL UPDATE syntax, all the records will get updated. Let us follow this with an example so that the exact meaning is very apparent.
A phone book is something every one of us use. If a typical phonebook was implemented in an RDBMS a table “PhoneDirectory” could look something like the table indicated below.
A simple table like this could be updated manually. When the phone book is large, for example, the public phone book for the organization, updating will need database support. One of the most common changes that can happen is that the person may have switched over to another company. His or her work phone or home phone could change. SQL UPDATE statement provides the means to make a change to the database, specifically to a particular record in the database.
For the sake of illustrating the use of the SQL UPDATE, let us assume Robert Halden has been transferred to a different city where the ABC, Inc. has an office. In such a case both his work and home phones would change. SQL UPDATE command for making these desired changes would look like the following.
SET WorkPhonenumber=’397-478-2294′, HomePhoneNumber=’397-225-8325′
WHERE ContactName=’Robert Halden’
This SQL UPDATE statement chooses the right table in a database and substitutes the work and home phone numbers of a specific record where the contact name is Robert Halden. The update happens in just one record that is required to be updated. If some particular column value(s) for all records were to be updated, dropping the WHERE clause of the SQL UPDATE command would do the job. The SET clause will specify the column and the value to be set in the complete database.