Re: select distnct limitations

"Ken Quirici" <kquirici_at_yahoo.com> a écrit dans le message de news: 3a5a1979-c420-4952-973f-d937cb7f7bc4_at_googlegroups.com...
| I'm somewhat confused by the Oracle 12c documentation on SELECT DISTINCT.
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| Specifically this extract:
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| "When you specify DISTINCT or UNIQUE, the total number of bytes in all select list expressions is limited to the size of a data
block minus some overhead. This size is specified by the initialization parameter DB_BLOCK_SIZE."
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| which is in the SQL User's Guide and Reference under SELECT.
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| I'm assuming it means you add up all the number of characters in the TEXT of the SQL statement in the DISTINCT list:
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| so "select distinct col1, col2, col3, col1+col3 ..."
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| has 21 bytes in its "select list expressions", which is less than most DB_BLOCK_SIZE values. This interpretation makes the
restriction on DISTINCT like the restriction on the ORDER BY list to 255 expressions, only more obscure.
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| Is this what the quoted extract above means? Or does it mean the total #bytes in each row of data retrieved must be a bit less
than DB_BLOCK_SIZE?

It is the size of the data in each row not the size of the text.

Regards
Michel Received on Thu Jun 12 2014 - 21:56:42 CEST