Make a web site - Books on Tape 5557076654 HarperCollins Publishers 246118318 Fawcett
Books on Tape 5557076654 HarperCollins Publishers 246118318 Fawcett Books 449208133 Berkley Publishing Group 9999999999 In this example, missing entries of both publishers and editions are replaced with NULL values. . Self Join Aself join simply joins a table to itself, and is commonly used with a table containing a hierarchy of records (a denormalized one-to-many relationship). Aself join does not require any explicit syntax other than including the same table in the FROM clause twice, as in the following example: SELECT P.NAME AS PARENT, C.NAME FROM SUBJECT P JOIN SUBJECT C ON (C.PARENT_ID = P.SUBJECT_ID); PARENT NAME —————- ——————— Non-Fiction Self Help Non-Fiction Esoteric Non-Fiction Metaphysics Non-Fiction Computers Fiction Science Fiction Fiction Fantasy Fiction Drama Fiction Whodunnit Fiction Suspense Fiction Literature Literature Poetry Literature Victorian Literature Shakespearian Literature Modern American Literature 19th Century American Nested Queries A nested query is a query containing other subqueries or queries contained within other queries. It is important to note that use of the term nested means that a query can be nested within a query, within a query, and so on more or less ad infinitum, or as much as your patience and willingness to deal with complexity allows. Some databases use the IN set operator to nest one query within another, where one value is checked for membership in a list of values. The following query finds all authors, where each author has a publication, each publication has an edition, and each edition has a publisher: SELECT * FROM AUTHOR WHERE AUTHOR_ID IN (SELECT AUTHOR_ID FROM PUBLICATION WHERE PUBLICATION_ID IN (SELECT PUBLICATION_ID FROM EDITION WHERE PUBLISHER_ID IN (SELECT PUBLISHER_ID FROM PUBLISHER))); AUTHOR_ID NAME ———- ——————– 2 James Blish 3 Isaac Azimov 4 Larry Niven 6 William Shakespeare 141 Reading and Writing Data with SQL
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