SQL Server 2019

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CREATE TABLE your_table (
  fruit    VARCHAR(32),
  color    VARCHAR(32)
);

INSERT INTO
  your_table
VALUES
  ('pear', 'red'),
  ('apple', 'green'),
  ('apple', 'golden')
3 rows affected

SELECT *
  INTO #temp
  FROM your_table
 WHERE fruit = 'apple' AND color = 'red'

IF (@@ROWCOUNT = 0)
  SELECT *
    FROM your_table
   WHERE fruit = 'apple'
ELSE
  SELECT *
    FROM #temp

DROP TABLE #temp


fruit
color


apple
green

apple
golden


SELECT *
  FROM your_table
 WHERE fruit = 'apple' AND color = 'red'

UNION ALL

SELECT *
  FROM your_table
 WHERE fruit = 'apple' AND NOT EXISTS (SELECT * FROM your_table WHERE fruit = 'apple' AND color = 'red')


fruit
color


apple
green

apple
golden


SELECT *
  FROM your_table
 WHERE fruit = 'apple'
   AND (
        color = 'red'
     OR NOT EXISTS (SELECT * FROM your_table WHERE fruit = 'apple' AND color = 'red')
   )


fruit
color


apple
green

apple
golden


INSERT INTO
  your_table
VALUES
  ('apple', 'red')
1 rows affected

SELECT *
  INTO #temp
  FROM your_table
 WHERE fruit = 'apple' AND color = 'red'

IF (@@ROWCOUNT = 0)
  SELECT *
    FROM your_table
   WHERE fruit = 'apple'
ELSE
  SELECT *
    FROM #temp

DROP TABLE #temp


fruit
color


apple
red


SELECT *
  FROM your_table
 WHERE fruit = 'apple' AND color = 'red'

UNION ALL

SELECT *
  FROM your_table
 WHERE fruit = 'apple' AND NOT EXISTS (SELECT * FROM your_table WHERE fruit = 'apple' AND color = 'red')


fruit
color


apple
red


SELECT *
  FROM your_table
 WHERE fruit = 'apple'
   AND (
        color = 'red'
     OR NOT EXISTS (SELECT * FROM your_table WHERE fruit = 'apple' AND color = 'red')
   )


fruit
color


apple
red