An interesting quirk:# select CASE WHEN '{"a":null}'::jsonb->>'a' IS NULL THEN 'yes' ELSE 'no' END;case------yes
According to the precedence table http://www.postgresql.org/docs/9.4/static/sql-syntax-lexical.html I would expect ->> to come under "all other native and user-defined operators", which would imply that this command should be testing whether 'a' IS NULL and applying the result (false) to the json operator - at which point we have# SELECT CASE WHEN '{"a":null}'::jsonb->>false THEN 'yes' ELSE 'no' END;and since
# SELECT '{"a":null}'::jsonb->>false;
returns NULL, the query is effectively:# SELECT CASE WHEN NULL THEN 'yes' ELSE 'no' END;which returns 'no'.So the only way that we should get 'yes' is if the ->> has higher precedence than 'IS NULL'.OK, so be it; except if we assume that the reason is because the lex analyzer sees '-' and assumes higher precedence than 'IS NULL' then you would expectSELECT '{"a":10}'::jsonb->>'a' - 5;to return '5' - since left-to-right precedence would make ->> run before the subtraction; however I get:ERROR: invalid input syntax for integer: "a"LINE 1:select '{"a":10}'::jsonb->>'a' - 5;
So what precedence level is ->> actually running at?Or am I missing something?
Looks correct to me. As I understand it the ::jsonb is NOT an operator! It is a syntactic construct for a CAST(). An equivalent which might make more sense is:
select CASE WHEN CAST('{"a":null}' AS JSONB)->>'a' IS NULL THEN 'yes' ELSE 'no' END;
Oh, an CAST() may look like a function call, but it is also a syntactic element. I.e. there is not a function called "CAST".
CheersGeoff
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10 to the 12th power microphones = 1 Megaphone
Maranatha! <><
John McKown
