Обсуждение: differences between <> and != when using signed values on the right hand side
differences between <> and != when using signed values on the right hand side
postgres=# select version();
version
---------------------------------------------------------------------------------------------------------------------------
PostgreSQL 16.3 (Debian 16.3-1.pgdg120+1) on aarch64-unknown-linux-gnu, compiled by gcc (Debian 12.2.0-14) 12.2.0, 64-bit
(1 row)
postgres=# select 1<>-1.0;
?column?
----------
t
(1 row)
postgres=# select 1<>-1;
?column?
----------
t
(1 row)
postgres=# select 1!=-1.0;
ERROR: operator does not exist: integer !=- numeric
LINE 1: select 1!=-1.0;
^
HINT: No operator matches the given name and argument types. You might need to add explicit type casts.
postgres=# select 1!=-1;
ERROR: operator does not exist: integer !=- integer
LINE 1: select 1!=-1;
^
HINT: No operator matches the given name and argument types. You might need to add explicit type casts.
select 1!= -1.0;
?column?
----------
t
(1 row)
Re: differences between <> and != when using signed values on the right hand side
When using a signed comparison != does not behave like <> if the right hand side comparator is signed and there is no space between the comparator and the sign
"David G. Johnston" <david.g.johnston@gmail.com> writes: > On Thursday, May 16, 2024, David Hunnisett <david.hunnisett@probit.io> > wrote: >> When using a signed comparison != does not behave like <> if the right >> hand side comparator is signed and there is no space between the comparator >> and the sign > This is not a bug. You are seeing practical examples of the behavior > documented here: > https://www.postgresql.org/docs/current/sql-syntax-lexical.html#SQL-SYNTAX-OPERATORS Yeah, it would probably have been better to forbid multicharacter operator names that end in '+' or '-'. But that ship sailed a long time ago, so we have this kluge to (effectively) allow it only if the operator can't be a SQL-standard one. Thus, in the example "!=-" is being read as a single operator name. regards, tom lane