Postgres update with an inner join across 3 tables? - sql

Question

This morning I asked this very similar question, and it was answered beautifully.
However, after reviewing the play, I see that my actual problem is slightly more complicated than what I described in that question. Basically, I have 3 Postgres tables:
[myschema].[animals]
--------------------
animal_id
animal_attrib_type_id (foreign key to [myschema].[animal_attrib_types])
animal_attrib_value_id (foreign key to [myschema].[animal_attrib_values])
[myschema].[animal_attrib_types]
--------------------------------
animal_attrib_type_id
animal_attrib_type_name
[myschema].[animal_attrib_values]
--------------------------------
animal_attrib_value_id
animal_attrib_value_name
So, I might have an animal record like so:
[myschema].[animals]
--------------------
animal_id = 458
animal_attrib_type_id = 38
animal_attrib_value_id = 23
And the corresponding animal_attrib_type (with id = 38) has the following values:
[myschema].[animal_attrib_types]
--------------------------------
animal_attrib_type_id = 38
animal_attrib_type_name = 'animals.should-make-noise'
And the corresponding animal_attrib_value (with id = 23) has the following values:
[myschema].[animal_attrib_values]
--------------------------------
animal_attrib_type_id = 23
animal_attrib_type_name = 'true'
So, the same animal record can have multiple type/value pairs. In this case the animal had an animal_attrib_type_name of "animals.should-make-noise" corresponding to an animal_attrib_value_name of "true".
At runtime, I will only have the animal_id (i.e, 458) and animal_attrib_type_id (i.e, 38). I need to be able to look up the appropriate animal_attrib_value_name corresponding to that given animal_id and animal_attrib_type_id only, and then update its value to some static text ('true' or 'false'); all from within the same UPDATE statement.
The answer in the above-referenced question was correct for the problem I stated, but since the same animal has 0+ type/value combos I actually need a slightly different SQL statement. Thanks in advance!

Answer 1

Make use of the FROM clause in the PostgreSQL UPDATE command. This is usually cleaner and faster.
UPDATE animal_attrib_values av
SET animal_attrib_value_name = 'true'
FROM animals a
WHERE a.animal_id = 458
AND a.animal_attrib_type_id = 38
AND a.animal_attrib_value_id = av.animal_attrib_value_id;
Since we already know the animal_attrib_type_id we don't have to include the third table animal_attrib_types at all. We could join to it additionally if needed ...
Also, do not table-qualify SET items in an UPDATE. That's a syntax error. I quote the manual on said page:
Do not include the table's name in the specification of a target
column — for example, UPDATE tab SET tab.col = 1 is invalid.
Bold emphasis mine.

Answer 2

The below SQL should do what you are asking:
UPDATE animal_attrib_values aav
SET animal_attrib_value_name= 'true'
WHERE aav.animal_attrib_value_id = (
SELECT a.animal_attrib_value_id
FROM animals a
WHERE a.animal_id = 458
AND a.animal_attrib_type_id = 38
)
;