Thread: PostgreSQL 9.5 operator precedence
<p><span style="font-family: 'Courier New','Courier';">Hello, </span><br /><span style="font-family: 'Courier New','Courier';">I'vegot a question about operator precedence is version 9.5</span><br /><br /><span style="font-family:'Courier New','Courier';">Versions lower than 9.5 worked well with constructions like</span><br /><spanstyle="font-family: 'Courier New','Courier';"> select a is null = b is null</span><br /><span style="font-family:'Courier New','Courier';">(it calculates if a is null, then if b is null and then compare two booleans)</span><br/><br /><span style="font-family: 'Courier New','Courier';">But now everything is changed, and official9.5 documentations says that </span><br /><span style="font-family: 'Courier New','Courier';">IS operator has lowerprecedence than = operator</span><br /><br /><span style="font-family: 'Courier New','Courier';">The thing I don't understandis the error message that I receive:</span><br /><br /><span style="font-family: 'Courier New','Courier';"> select1 is null = 2 is null;</span><br /><span style="font-family: 'Courier New','Courier';"> -----------------------------</span><br/><span style="font-family: 'Courier New','Courier';"> ERROR: operator does notexist: boolean = integer</span><br /><span style="font-family: 'Courier New','Courier';"> LINE 1: select 1 is null= 2 is null</span><br /><span style="font-family: 'Courier New','Courier';"> ^</span><br/><span style="font-family: 'Courier New','Courier';"> HINT: No operator matches the given name and argumenttype(s). You might need to add explicit type casts.</span><br /><br /><span style="font-family: 'Courier New','Courier';">Forme it means that postgres calculated value in the left side of the = operator, then it decided not tocalculate right side and compare boolean and integer.</span><br /><span style="font-family: 'Courier New','Courier';">Whydid it not compare null and 2 firstly? </span><br /><span style="font-family: 'Courier New','Courier';">Maybethe truth is IS operator and = operator has the same precedence, and then calculated from left to right?</span><br/><span style="font-family: 'Courier New','Courier';">Maybe I miss something?</span><br /><br /><span style="font-family:'Courier New','Courier';">Best Regards,</span><br /><span style="font-family: 'Courier New','Courier';">Andrew</span><br/><br /><br /><br /><br /><br />
Hello,
I've got a question about operator precedence is version 9.5
Versions lower than 9.5 worked well with constructions like
select a is null = b is null
(it calculates if a is null, then if b is null and then compare two booleans)
But now everything is changed, and official 9.5 documentations says that
IS operator has lower precedence than = operator
The thing I don't understand is the error message that I receive:
select 1 is null = 2 is null;
-----------------------------
ERROR: operator does not exist: boolean = integer
LINE 1: select 1 is null = 2 is null
^
HINT: No operator matches the given name and argument type(s). You might need to add explicit type casts.
Your query reads:
SELECT ( ( 1 IS (NULL = 2) ) IS NULL
)
So the error is in:
1 IS (NULL = 2)
which indeed is integer = boolean
David J.
"David G. Johnston" <david.g.johnston@gmail.com> writes:
> On Mon, Sep 19, 2016 at 11:02 PM, Андрей Авакимов <aquarius1993@rambler.ru>
>> The thing I don't understand is the error message that I receive:
>> select 1 is null = 2 is null;
>> -----------------------------
>> ERROR: operator does not exist: boolean = integer
>> LINE 1: select 1 is null = 2 is null
> Your query reads:
> SELECT ( ( 1 IS (NULL = 2) ) IS NULL
No, certainly not that --- IS isn't some sort of standalone operator,
rather IS NULL is an indivisible combination of tokens representing a
postfix operator. The query's really getting parsed like this:
select ((1 is null) = 2) is null;
whereas the pre-9.5 interpretation was
select (1 is null) = (2 is null);
If you add those parentheses explicitly then your query will work fine
in either version.
regards, tom lane