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How would one properly write a FUNCTION in postgres to return a TABLE based on a query where the query WHERE clause can have both an unknown number of filter conditions, and the conditions themselves are dynamic?

I feel like this should be a solved problem, and maybe it is, but I am unable to find any examples in postgres.

The type of conditions in involved in building one filter condition would be dynamically setting AND, OR, NOT conditions, =, >, <, >=, <=, etc. for a given column's values.

Then multiply this by an unknown n number of possible filter conditions.

In my scenario at the moment, there are nearly 70 different numerical measures which could be used to compose the where clause. Again, each of these measures could have AND, OR, NOT conditions, =, >, <, >=, <=, etc. applied. Moreover, each one of these 70 different numerical measures could be used more than once if different equality operators and low/high limit ranges are applied. At a 30,000 ft view, think of the problem as passing all the conditions you could generate in a tool like this to a postgres query. Essentially you would be translating into a postgres query the results of a web app end-user who is building a cohort from visual tools with 70+ measures at his/her disposal.

What is the best way to go about this in postgres? Pass a json array of objects as a function parameter, convert them to a table, and base the dynamic where in some manner off of that table? Run a LOOP based off the conditions? Other? Appreciate any help getting un-stuck on this challenge.

  • May I ask what you want to use this for? – Philᵀᴹ Nov 14 '18 at 0:43
  • With everything completely dynamic and no limits, there are various pitfalls to steer clear of. Typically, there are more confining specs ... Here is a detailed related answer - from 2013: stackoverflow.com/a/17355733/939860 – Erwin Brandstetter Nov 14 '18 at 1:05
  • @Philᵀᴹ - I've tried to make that clearer by adding more context to my question. – mg1075 Nov 14 '18 at 4:24
  • @ErwinBrandstetter - I need to account for at minimum about 70 different measures, and each of these measures can have different equality operators applied to them. And, optimally, I want the end user to be able to apply more than one condition on a measure. I'm worried the complexity of such a query, although using dynamic sql as e.g. here - stackoverflow.com/a/12047277/538962 - would be a maintenance headache. – mg1075 Nov 14 '18 at 4:32
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Have the function take a structure that defines the constraint to apply and parse that structure into a SQL where expression, then execute it.

The structure could be represented as JSON, XML, or any other type that can be handled by postgresql built-ins or your code.

For safety aghainst injection attacks be sure to not copy any raw data from the struct to the query, all values and identifiers should be quoted (quote_identifier(), quote_nullable(), etc...) and all operators should come from string literals in the function code.

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