Combining Insert and Update SQL Logic

*Note that this example is using MSSQL with an Identity set to generate the primary key automatically.

An all too common process developers go through when building database driven web applications is creating logic to INSERT a record when one doesn’t exist, and UPDATE a record when one does exist.

This often leads to conditional logic within your application (inside a Service layer perhaps) and then running one of 2 SQL statements depending on the existance of a primary key value which may be coming from a form or URL.

You would more than likely have separate methods for INSERTING and UPDATING, but for the sake of simplicity these will be together:

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<cfif len(form.myPrimaryKey)>

  <!--- there is a primary key meaning a record exists, UPDATE --->
  <cfquery name="qSetData" datasource="dsn">
      UPDATE  myTable
      SET     field1 = '#trim(form.field1)#'
              , field2 = '#trim(form.field1)#'
      WHERE   myPrimaryKey = #form.myPrimaryKey#
  </cfquery>

<cfelse>
  
<!--- there is no primary key meaning a record doesn't exists, INSERT a new row --->
 <cfquery name="qCreateData" datasource="dsn">
     INSERT INTO myTable (field1, field2)
     VALUES              ('#trim(form.field1)#', '#trim(form.field1)#')
  </cfquery>

</cfif>

That’s it, this approach is a nice way to start examining you DAO’s.

Another way to achieve this is by using a stored procedure (there are many, many positive reasons for using a stored procedure. See here and here for more information).

Using a stored procedure can be cleaner as you just need the one piece of code in your application leaving the rest of the logic to be handled in the database.

The following example is for scenarios where you don’t pass a primary key value, the will pass null=”true” to the stored procedure. This is how the SQL will know to run an INSERT statement.

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<cfscript>
  //as there is no value here an INSERT statement will be run
  myPrimaryKey = "";
  firstName = "Michael";
  lastName = "Sharman";
  email = "michael@wherever.com";
  age = "31";
</cfscript>

<cfstoredproc datasource="dsn" procedure="setUser">
  <cfprocparam cfsqltype="CF_SQL_INTEGER" null="#NOT len(trim(myPrimaryKey))#" value="#myPrimaryKey#" />
  <cfprocparam cfsqltype="CF_SQL_VARCHAR" null="false" value="#firstName#" />
  <cfprocparam cfsqltype="CF_SQL_VARCHAR" null="false" value="#lastName#" />
  <cfprocparam cfsqltype="CF_SQL_VARCHAR" null="false" value="#email#" />      
  <cfprocparam cfsqltype="CF_SQL_INTEGER" null="#age#" value="#age#" />
</cfstoredproc>

On the other hand if I have a primary key value, the will pass the value (with null=”false”) and my stored procedure will run an UPDATE.

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<cfscript>
  //as there is a value here an UPDATE statement will be run
  myPrimaryKey = "13";
  firstName = "Michael";
  lastName = "Sharman";
  email = "michael@wherever.com";
  age = "31";
</cfscript>

<cfstoredproc datasource="dsn" procedure="setUser">
  <cfprocparam cfsqltype="CF_SQL_INTEGER" null="#NOT len(trim(myPrimaryKey))#" value="#myPrimaryKey#" />
  <cfprocparam cfsqltype="CF_SQL_VARCHAR" null="false" value="#firstName#" />
  <cfprocparam cfsqltype="CF_SQL_VARCHAR" null="false" value="#lastName#" />
  <cfprocparam cfsqltype="CF_SQL_VARCHAR" null="false" value="#email#" />      
  <cfprocparam cfsqltype="CF_SQL_INTEGER" null="#age#" value="#age#" />
</cfstoredproc>

You can see that the only change was that in the second example myPrimaryKey actually had a value.

And now for the simple stored procedure. Note I’m setting a default value of null for the @myPrimaryKey parameter, this is how the stored procedure can handle both scenarios. You can of course set default values for all of your parameters.

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CREATE PROCEDURE setUser
(
@myPrimaryKey int = null
,@firstName varchar(50)
,@lastName varchar(50)
,@email varchar(50)
, @age int
)
AS

IF (@myPrimaryKey Is Null)
BEGIN
  --no record exists so run an INSERT statement
  INSERT INTO myTable(FirstName, LastName, Email, Age)
  VALUES      (@firstName, @lastName, @email, @age)
END
ELSE
BEGIN
  --we have a record, run an UPDATE
  UPDATE  myTable
  SET     firstName = @firstName
          , lastName = @lastName
          , email = @email
          , age = @age
  WHERE   myPrimaryKey = @myPrimaryKey
END
GO

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