James Blish (Web site management) Isaac Azimov Larry Niven Jerry Pournelle
Friday, August 31st, 2007James Blish Isaac Azimov Larry Niven Jerry Pournelle William Shakespeare Kurt Vonnegut Execute an expression on a single field of the AUTHOR table, returning a small section of the author s name: SELECT AUTHOR_ID, SUBSTR(NAME,1,10) FROM AUTHOR; AUTHOR_ID SUBSTR(NAM ———- ———- 1 Orson Scot 2 James Blis 3 Isaac Azim 4 Larry Nive 5 Jerry Pour 6 William Sh 7 Kurt Vonne Execute an expression, but this time involving more than a single field: SELECT E.ISBN, (E.LIST_PRICE * R.RANK) + R.INGRAM_UNITS FROM EDITION E JOIN RANK R ON (R.ISBN = E.ISBN); ISBN (E.LIST_PRICE*R.RANK)+R.INGRAM_UNITS ———- ———————————— 198711905 46072.5 345308999 9728 345336275 11860 345438353 24200 553278398 14430 553293362 7985 553293370 14815 553293389 8370 893402095 14026.5 1585670081 34600 5557076654 37632.5 Use aliases as substitutes for table names: SELECT A.NAME, P.TITLE, E.ISBN FROM AUTHOR A JOIN PUBLICATION P USING (AUTHOR_ID) Retrieving specific field names is very slightly more efficient than retrieving all fields using the * character. The * character requires the added overhead of metadata interpretation lookups into the metadata dictionary to find the fields in the table. In highly concurrent, very busy databases, continual data dictionary lookups can stress out database concurrency handling capacity. 128 Chapter 5
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