SOQL Query – How to Replace a SOQL Query with a String

Lets say you have the following strings.

String1 = 'myString/myPattern/someString'
String2 = 'newString'

You can append your new string just before the required pattern like this.

String newString = 
    String1.substring(0, String1.indexOf('/myPattern')) +
    String2 + 
    String1.substring(String1.indexOf('/myPattern'), String1.length());

But make sure your pattern is not repeated in the String1, because you might end up replacing just the first occurrence.

    DateTime dt = DateTime.now();
    String formattedDt = dt.format('yyyy-MM-dd\'T\'hh:mm:ss\'Z\'');

Update: Another option is to use SOQL dynamic binding, no formatting required.

    DateTime dt = DateTime.now();
    String query = 'SELECT Id FROM User WHERE  SystemModstamp > :dt '
    List<SObject> results = Database.query(query);