Re: [HACKERS] Index expression syntax

[Konstantin Knizhnik]

On 29.09.2017 11:03, Marko Tiikkaja wrote:
On Fri, Sep 29, 2017 at 9:31 AM, Konstantin Knizhnik 
> wrote:


I wonder why syntax error is produced in this case:

postgres=# create index metaindex on foo using
gin(to_tsvector('english', x)||to_tsvector('english',y));
ERROR:  syntax error at or near "||"
LINE 1: ...taindex on foo using gin(to_tsvector('english',
x)||to_tsvec...
^
[ .. ]

/|expression:|/
An expression based on one or more columns of the table. The
expression usually must be written with surrounding
parentheses, as shown in the syntax. However, the parentheses
can be omitted if the expression has the form of a function call.

So documentations states that sometimes it is possible to avoid
parentheses, but it is unclear why I have to use double
parentheses...
I think that either grammar should be fixed, either documentation
should be updated.


Your expression is clearly not a function call, it's a concatenation 
of two of them.  The documentation seems perfectly accurate to me?



O, sorry!
You are right. I just didn't notice extra parenthesis in CREATE INDEX 
syntax in case of using expressions.


--
Konstantin Knizhnik
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company

Re: [HACKERS] Index expression syntax

[Marko Tiikkaja]

On Fri, Sep 29, 2017 at 9:31 AM, Konstantin Knizhnik <
k.knizh...@postgrespro.ru> wrote:

> I wonder why syntax error is produced in this case:
>
> postgres=# create index metaindex on foo using gin(to_tsvector('english',
> x)||to_tsvector('english',y));
> ERROR:  syntax error at or near "||"
> LINE 1: ...taindex on foo using gin(to_tsvector('english', x)||to_tsvec...
>  ^
> [ .. ]
>
> *expression:* An expression based on one or more columns of the table.
> The expression usually must be written with surrounding parentheses, as
> shown in the syntax. However, the parentheses can be omitted if the
> expression has the form of a function call.
>
> So documentations states that sometimes it is possible to avoid
> parentheses, but it is unclear why I have to use double parentheses...
> I think that either grammar should be fixed, either documentation should
> be updated.
>

Your expression is clearly not a function call, it's a concatenation of two
of them.  The documentation seems perfectly accurate to me?


.m

[HACKERS] Index expression syntax

[Konstantin Knizhnik]

I wonder why syntax error is produced in this case:

postgres=# create index metaindex on foo using 
gin(to_tsvector('english', x)||to_tsvector('english',y));

ERROR:  syntax error at or near "||"
LINE 1: ...taindex on foo using gin(to_tsvector('english', x)||to_tsvec...
 ^
The error can be eliminated if extra surrounding parentheses are added:

postgres=# create index metaindex on foo using 
gin((to_tsvector('english', x)||to_tsvector('english',y)));

CREATE INDEX

Postgresql documentations says:

CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ [ IF NOT EXISTS ]/|name|/  ] 
ON/|table_name|/  [ USING/|method|/  ]
( {/|column_name|/  | (/|expression|/  ) } [ COLLATE/|collation|/  ] 
[/|opclass|/  ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ] [, ...] )
[ WITH (/|storage_parameter|/  =/|value|/  [, ... ] ) ]
[ TABLESPACE/|tablespace_name|/  ]
[ WHERE/|predicate|/  ]

/|expression:|/
   An expression based on one or more columns of the table. The
   expression usually must be written with surrounding parentheses, as
   shown in the syntax. However, the parentheses can be omitted if the
   expression has the form of a function call.

--





So documentations states that sometimes it is possible to avoid 
parentheses, but it is unclear why I have to use double parentheses...
I think that either grammar should be fixed, either documentation should 
be updated.

/||/

--
Konstantin Knizhnik
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company