Sql updating primary key value
If a table has a primary key defined on any field(s), then you cannot have two records having the same value of that field(s).
Note − You would use these concepts while creating database tables.
When rows are combined duplicate rows are eliminated.In simple terms, joins combine data into new columns.If two tables are joined together, then the data from the first table is shown in one set of column alongside the second table’s column in the same row. If two tables are “unioned” together, then the data from the first table is in one set of rows, and the data from the second table in another set. Each row in the result contains columns from BOTH table A and B.You would like to create a master list of name and birth days sorted by date. It is one of the most common forms of join and is used when you need to match rows from two tables.To do this you can use a union to first combine the rows into a single result and then sort them. Rows that match remain in the result, those that don’t are rejected.