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Comparison Operators in SOQL:    

Using of this comparison operator we will compare the values in where Condition.

Operator	Description
=	Equals (Using of the Equals We will compare two different values) Return true if both values compare.
!=	Not Equals (Using of the Not Equals We will compare two Different values) Return true if both values not compare.
<	Less than
<=	Less than or equal
>	Greater than
>=	Less than or equal
>	Greater than
>=	Greater than or equal
IN	In
NOT IN	Not in (WHERE clause)
INCLUDES EXCLUDES	Applies to multi-select picklists

Some Examples on SOQL:      

I want display all the accounts in a Table ? What we need to do?                  

Page:

 <apex:page controller="SOQLDemo" sidebar="false">

     <apex:form >

         <apex:pageBlock title="SOQL Demo">

             <apex:pageBlockSection title="SOQL Demo" columns="1">

                 <apex:pageBlockTable value="{!Accountdata}" var="s">

                     <apex:column value="{!s.Name}"/>

                     <apex:column value="{!s.ID}"/>

                     <apex:column value="{!s.Phone}"/>

                 </apex:pageBlockTable>       

             </apex:pageBlockSection>

         </apex:pageBlock>        

     </apex:form>

</apex:page> 

Class:

public class SOQLDemo

{   

    public  list<Account> Accounts{get;set;}

    Public list<Account> getAccountdata()

    {

        Accounts = [select id,Name,phone from Account];

        return Accounts ;        } }

SOQL Joins & Soql Locking statements:

Using of the SOQL Joins we will retrieve the data from their related object.

Example:

Q1. I want to write a query on Child object and we need to retrieve their related Parent records?

              Select id,Name,Phone,Email,Account.Name from contact

We are writing query on Parent object and we are retrieving the records from their related Parent.

Q2. I want to write a query on Parent object and we need to retrieve their related child records?

                Select id,Name,(select id,Name from contact) from Account

Here we are retrieving the Account their related contacts.

SOQL Locking Statement:

Using of the SOQL Update statement we will lock the SObject records in Salesforce. While a sObject record is locked, no other client or user is allowed to make updates either through code or the Salesforce user interface. The lock gets released when the transaction completes.

Syntax: Select id,Name,Phone from Account where Name=’IBM’ For Update;

During this transaction we cannot edit these IBM records using Data management Tools are UI.

Important Points on SOQL Update:

•       While the records are locked by a client, the locking client can modify their field values in the database in the same transaction.
• Other clients have to wait until the transaction completes and the records are no longer locked before being able to update the same records. Other clients can still query the same records while they’re locked
•   We cannot specify the Order by if you are using SOQL update statement.
•   The Apex runtime engine locks not only the parent sObject record but all child records as well. So if you lock the parent object records all the associate child records also got locked.   Syntax:

                Select Field1, Field 2, Field 3 --- from Object FOR Update

Example Code:

Public class SOQLlocking

{

                Public list<Account> getAccountRecords()

{

list<Account> AccountRecords = [select id,Name,Phone from Account where Name Like     ‘%Karthik Training%’ FOR Update];

return AccountRecords;

}

}

In the above Code I lock all the Karthik Training records, while this transaction  any user try to change the record user will notify with the error.

Once the transaction completed then we will update this records also.

 SOQL Interview questions:

     1. What is SOQL?

SOQL stands for Salesforce object query language, using of the SOQL we will retrieve the data from single object and related object.

Ex: if we want to retrieve the data from Account object,

    Select id,Name,Phone  from Account

      2. What are the Governor limits of SOQL?

We will write maximum of 100 SOQL, using of one SOQl we will retrieve 50000 records.

Total number of SOQL queries issued for Batch Apex and future methods is 200

3   3.  What is the return type for SOQL queries?

Soql will return Integer datatype, List of Sobject and Single subject.