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MERGE INTO targetTable t USING sourceTable s ON t.PKID = s.PKID WHEN MATCHED AND NOT EXISTS ( SELECT s.ColumnA, s.ColumnB, s.ColumnC INTERSECT SELECT t.ColumnA, t.ColumnB, s.ColumnC ) THEN UPDATE SET t.Colum...

Suppose we want to know how many users have the same name. Let us create table users as follows: create table users( id int primary key auto_increment, name varchar(8), count int, unique key name(name) ); Now, we just discovered a new user named Joe and would like to take hi...

Suppose we want to know how many users have the same name. Let us create table users as follows: create table users( id serial, name varchar(8) unique, count int ); Now, we just discovered a new user named Joe and would like to take him into account. To achieve that, we need to d...