Database Administration Questions

A search engine is a set of programs which enables users to search documents and files ihe world wide web.

Common search engines are Google, Yahoo, Bing,...

Venus planet is known as the Morning Star or the Evening Star.

A candidate key is a column, or set of columns, in a table that can uniquely identify any database record without referring to any other data. Each table may have one or more candidate keys, but one candidate key is unique, and it is called the primary key.

I am History.

Yes, history refers to all the past, but we can create history in the presentand it cannot be polluted in the future.

The three major amendments that were passed shortly after the Civil War are the reconstruction amendments that were the 13th, 14th, and 15th amendments.

The 13th Amendment abolished slavery,

The 14th granted African American citizenship and equal protection before the law, (and)

The 15th Amendment attempted to secure the right to vote for newly freed slaves. 

The difference between Union and Union all is that Union all will not eliminate duplicate rows, instead it just pulls all rows from all tables fitting your query specifics and combines them into a table. A UNION statement effectively does a SELECT DISTINCT on the results set.

Foreign keys are the columns of a table that points to the primary key of another table. They act as a cross-reference between tables.

In detail : A Foreign key is a field (or collection of fields) in one table that uniquely identifies a row of another table or the same table. In simpler words, the foreign key is defined in a second table, but it refers to the primary key or a unique key in the first table.