make email or tel row in table a UNIQUE constraint

[jdzine92]

This will prevent duplicate records of the same customer. Assigning by oid is not enough to prevent this from happening.

[jdzine92]

The following illustrates how to define a UNIQUE constraint for multiple columns: (email/tel)
See: https://www.sqlitetutorial.net/sqlite-unique-constraint/

CREATE TABLE table_name(
...,
UNIQUE(column_name1,column_name2,...)
);