sql select unique values from column code example

Example 1: how to select unique element in sql

DISTINCT
- select distinct * from employees; ==> 
  retrieves any row if it has at
  least a single unique column.

- select distinct first_name from employees; ==> 
      retrieves unique names
     from table. (removes duplicates)
     
- select distinct count(*) from employees;
     retrieve number of unique rows
     if any row has at least a single unique data.

Example 2: select only unique values from and to current table

INSERT INTO Table2(Id) SELECT DISTINCT Id FROM Table1 WHERE Id NOT IN(SELECT Id FROM Table2);

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Sql Example

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