On Fri, Aug 18, 2017 at 10:47:37PM +0200, Peter J. Holzer wrote: > On 2017-08-18 06:37:15 -0500, Justin Pryzby wrote: > > On Fri, Aug 18, 2017 at 01:01:45PM +0200, Rob Audenaerde wrote: > > > I don't understand why this query: > > > > > > select count(base.*) from mytable base; > > > > > > does return multiple rows. > > > > > > select count(1) from mytable base; > > > > > > returns the proper count. > > > > > > There is a column with the name 'count'. > > > > > > Can anyone please explain this behaviour? > > > > https://www.postgresql.org/docs/9.6/static/sql-expressions.html#SQL-EXPRESSIONS-FUNCTION-CALLS > > https://www.postgresql.org/docs/9.6/static/rowtypes.html#ROWTYPES-USAGE > > Maybe I overlooked it, but I don't see anything in those pages which > explains why «count» is parsed as a column name in the first example and > as a function name in the second. > > Nor do I see what «count(base.*)» is supposed to mean. It seems to be > completely equivalent to just writing «count», but the part in > parentheses is not ignored: It has to be either the table name or the > table name followed by «.*». Everything else I tried either led to a > syntax error or to «count» being recognized as a function. So apparently > columnname open-parenthesis tablename closed-parenthesis is a specific > syntactic construct, but I can't find it documented anywhere. | Another special syntactical behavior associated with composite values is that |we can use functional notation for extracting a field of a composite value. The |simple way to explain this is that the notations field(table) and table.field |are interchangeable. For example, these queries are equivalent: | Tip: Because of this behavior, it's unwise to give a function that takes a |single composite-type argument the same name as any of the fields of that |composite type. If there is ambiguity, the field-name interpretation will be |preferred, so that such a function could not be called without tricks. One way |to force the function interpretation is to schema-qualify the function name, |that is, write schema.func(compositevalue). pryzbyj=# select base.count from s91 base; count ------- 1 2 3 (3 rows) pryzbyj=# select pg_catalog.count(base.*) from s91 base; count | 3 -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
