根据多个参数搜索postgres表，但不需要全部

Question

I am trying to create a query where I search through 1 table based upon 4 values. None of these values are required and it should return based upon all of them.

The below is how I would do it if all values would always be provided.

CREATE OR REPLACE FUNCTION "GetValues"(
  "@value1"                TEXT,
  "@value2"                TEXT,
  "@value3"                TEXT
  "@value4"                TEXT
)
RETURNS TABLE(
  "id"                     UUID,
  "@value1"                TEXT,
  "@value2"                TEXT,
  "@value3"                TEXT
  "@value4"                TEXT  
) AS
$func$
BEGIN
  RETURN QUERY SELECT
    c."id",
    c."value1",
    c."value2",
    c."value3",
    c."value4"
  FROM "values" AS v
  WHERE "value1" = "@value1"
  AND "value2" = "@value2"
  AND "value3" = "@value3"
  AND "value4" = "@value4";
END;
$func$ LANGUAGE PLPGSQL;

The below is how I imagine doing it but I can't get anything like that to work within it.

IF ("@value1" IS NOT NULL) THEN
  WHERE "value1" = "@value1"
END IF;

Am I supposed to do many individual SELECTS and then combine them all with UNION? I don't think that will work because I only want what matches all criteria to show up?

Answer 1

Use COALESCE() :

SELECT
    "id",
    "value1",
    "value2",
    "value3",
    "value4"
FROM "values"
WHERE "value1" = COALESCE("@value1", "value1")
AND "value2" = COALESCE("@value2", "value2")
AND "value3" = COALESCE("@value3", "value3")
AND "value4" = COALESCE("@value4", "value4")

Working example in rextester.

Not related but important. Using table or column names in double quotes definitely does not make life easier. The name "values" for a table may be considered a bad practice.