How to convert PostgreSQL 9.4's jsonb type to float

Question

I\'m trying the following query:

SELECT (json_data->\'position\'->\'lat\') + 1.0 AS lat FROM updates LIMIT 5;

(The +1.0 is just there

Answer 1

Now we can do it!

In nowadays we can cast directly from JSONb to SQL datatypes. I am using PostgreSQL v12.3, where it is working fine:

SELECT (j->'i')::int, (j->>'i')::int, (j->'f')::float, (j->>'f')::float
FROM  (SELECT '{"i":123,"f":12.34}'::jsonb) t(j); 

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Sub-questions:

• From which version is it possible?

• It is a syntax sugar or a real conversion?

• If real "binary JSONb → binary SQL" conversion, where the micro-optimizations?
  For example, what wold be faster (?) tham "binary JSONb → string → binary SQL"? boolean→boolean, number→numeric, number→int, number→bigint; number→flloat, number→double.

• Why not optimized for NULL?
  Curiosily the "NULL to SqlType" not works, "ERROR: cannot cast jsonb null to type integer".

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Benchmark suggestion

How to check? When PostgreSQL optimize loop queries?

EXPLAIN ANALYSE SELECT (j->'i')::int, (j->'f')::float       -- bynary to bynary INT and FLOAT
-- EXPLAIN ANALYSE SELECT (j->>'i')::int, (j->>'f')::float  -- string to bynary INT and FLOAT

-- EXPLAIN ANALYSE SELECT (j->'i')::numeric, (j->'f')::numeric    -- bynary to bynary NUMERIC
-- EXPLAIN ANALYSE SELECT (j->>'i')::numeric, (j->>'f')::numeric  -- string to bynary NUMERIC

FROM (
  SELECT (('{"i":'||x||',"f":'||x||'.34}')::jsonb) as j FROM  generate_series(1,599999) g(x)
  -- SELECT (('{"i":123,"f":12.34}')::jsonb) as j FROM  generate_series(1,599999) g(x)
) t;