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 fieldconstraint 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 fieldunique 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.Copyright © 2021 Codeinu
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