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SELECT * INTO

We can create a table with the select command as well. General syntax to create a table with the select command is : 

      SELECT * 
       INTO <YourNewTable>
      FROM <YourTable>

While using "SELECT * INTO " command we should keep following concepts in mind.
  1. Identity Columns
    1. if using simple select operation, new table will inherit the Identity property
    2. New table will not inherit the Identity property for following cases
      1. Identity columns are listed more than one time in select list
      2. Using multiple select operations with UNION or UNION ALL clause
      3. Identity column is a part of an expression
    3. If identity column is required in destination table but not available in source result-set you can define your own identity function e.g. 

      -- -- Step 1. Create a table "Table_1" with identity column (ID)
-- CREATE TABLE TABLE_1 (ID INT IDENTITY(1,1) PRIMARY KEY, Name VARCHAR(20))

-- -- Step2. Insert some records
--INSERT INTO table_1(Name) values ('Ram'), ('Shyam'), ('Sohan')

---- Step3. (ERROR) Create new table "Table_2" suing "SELECT INTO" statement
---- (try adding your own Id identity )
---- IT WILL GIVE AN ERROR AS "ID" Column in Source table is already AN IDENTITY COLUMN

--SELECT IDENTITY(INT, 1,1) AS MyIdentityId
-- , ID AS ExistingId
-- , Name
--INTO Table_2
--FROM table_1

---- Step4. (SUCCESS) Create new table "Table_2" using "SELECT INTO" statement
---- try using your own identity column, with expression (cast function) in existing ID column
---- It will successfully get executed with new table "Table_2" having "MyIdentityId" as an Identity column

--SELECT IDENTITY(INT, 1,1) AS MyIdentityId
-- , CAST(ID AS int) AS ExistingId
-- , Name
--INTO Table_2
--FROM table_1

  2. Indexes, constraints & triggers will not get transferred from the source table to destination table If it's required you've to create it explicitly.

  3. Order by clause doesn't guarantee the data will get inserted in the same order

  4. If we're using any expression in select statement (e.g. some computation), it doesn't create the computed column into the destination table instead exact data will get inserted


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