1. Union
select id from t_book;
select id from t_bookType;
select id from t_book union select id from t_bookType;

2. Union all
select id from t_book union all select id from t_bookType;

3. Alias
select * from t_book tb where tb.id>=3;
select tb.id, tb.bookName from t_book tb where tb.id>=3;
select tb.id, tb.bookName Book_Name from t_book tb where tb.id>=3;
select tb.id, tb.bookName as Book_Name from t_book tb where tb.id>=3;


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