title: Cannot insert duplicate key row in object with unique index The duplicate key value SQL Server
body: <p>I'm getting this error:</p>
  
  <blockquote>
    <p>Cannot insert duplicate key row in object 'dbo.CLIENT' with unique
    index 'CLIENT_idx_A'. The duplicate key value is (14441828, 1).</p>
  </blockquote>
  
  <p>When I checked, the indexes, it's created like this:</p>
  
  <pre><code>CREATE UNIQUE NONCLUSTERED INDEX [CLIENT_idx_A] ON [dbo].[CLIENT] 
  (
       [SOURCE_SYSTEM_CLIENT_ID] ASC,
       [SOURCE_SYSTEM_ID] ASC
  )
       WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE  = OFF,
             SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF,
             DROP_EXISTING = OFF, ONLINE = OFF,
             ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON)
  ON [PRIMARY]
  </code></pre>
  
  <p>Actually, I want to update one value in <code>SOURCE_SYSTEM_CLIENT_ID</code> and my <code>SOURCE_SYSTEM_ID</code> is 1 for all the <code>SOURCE_SYSTEM_CLIENT_ID</code> that I want to update. So I think, its encountering duplicate. How can I solve this? </p>