make column unique in mysql code example
Example 1: mysql query unique column
SELECT DISTINCT(column_name) FROM your_table_name;
#You can select distinct values for one or more columns. The column names has to be separated with comma.
SELECT DISTINCT column_name_1, column_name_2 FROM your_table_name;
Example 2: mysql set field unique
ALTER TABLE mytbl ADD UNIQUE (columnName);
Example 3: mysql alter table set column unique
ALTER TABLE contacts
ADD CONSTRAINT contacts_unique UNIQUE (reference_number);