MySQL 5.7

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SET @j = '[{"x":"Abc"}, {"y":"bcd"}, {"z":"ABC"}, {"w":"abc"}]';
SELECT JSON_SEARCH(@j, 'one', 'ABC'); 

JSON_SEARCH(@j, 'one', 'ABC')

"$[2].z"

SELECT JSON_SEARCH(@j, 'one', LOWER('ABC')); 

JSON_SEARCH(@j, 'one', LOWER('ABC'))

"$[3].w"

SELECT JSON_SEARCH(LOWER(@j), 'one', LOWER('ABC')); 

JSON_SEARCH(LOWER(@j), 'one', LOWER('ABC'))

"$[0].x"

SELECT JSON_SEARCH(LOWER(@j), 'all', LOWER('ABC')); 

JSON_SEARCH(LOWER(@j), 'all', LOWER('ABC'))

["$[0].x", "$[2].z", "$[3].w"]