Answers for "sqlserver unique constraint by query"

SQL
7

constraint unique sql

ALTER TABLE table_name ADD CONSTRAINT cst_name UNIQUE (col_name); 
ALTER TABLE table_name ADD CONSTRAINT cst_name UNIQUE (col1, col2); -- Multiple
ALTER TABLE table_name ADD col_name NUMBER UNIQUE;				  	-- New field
Posted by: Guest on July-03-2021
0

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.
Posted by: Guest on January-28-2021

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