SOQL
using string literals
Literal strings must be enclosed in single quotation marks. double quotation marks are reserved for enclosing attribute values, and must be escaped in strings. Use the “\” character to escape strings.
lock record using SOQL so that it cannot be modified by other user
we will need “FOR UPDATE” clause of SOQL. Account[] accts = [SELECT Id FROM Account LIMIT 2 FOR UPDATE];
SOQL statement can be used to get all records even from recycle bin
We will need “ALL Rows” clause of SOQL. SELECT COUNT() FROM Contact WHERE AccountId = a.Id ALL ROWS