Re: 7.2. Table Expressions suggestion about NATURAL JOIN
От | Grzegorz Szpetkowski |
---|---|
Тема | Re: 7.2. Table Expressions suggestion about NATURAL JOIN |
Дата | |
Msg-id | BANLkTine881x0Jb8NeO38baToKhZ3HHybA@mail.gmail.com обсуждение исходный текст |
Ответ на | 7.2. Table Expressions suggestion about NATURAL JOIN (Grzegorz Szpetkowski <gszpetkowski@gmail.com>) |
Список | pgsql-docs |
2011/5/18 Grzegorz Szpetkowski <gszpetkowski@gmail.com>: > http://www.postgresql.org/docs/9.0/static/queries-table-expressions.html > http://www.postgresql.org/docs/9.0/static/sql-select.html > > Respectively: > > "Finally, NATURAL is a shorthand form of USING: it forms a USING list > consisting of all column names that appear in both input tables. As > with USING, these columns appear only once in the output table." > > and > > "NATURAL is shorthand for a USING list that mentions all columns in > the two tables that have the same names." > > To make that comprehensive you can add something like: "Note that if > there is no any "shared" column between tables, then NATURAL JOIN acts > like ON TRUE (that is, tables are cross-joined)", because it's not > obvious. > > thanks & regards, > greg szpetkowski > My mistake "NATURAL JOIN", better is to just write "NATURAL". thanks & regards, greg szpetkowski
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