SQL query to determine if a JSON value contains a specified attribute

I assume you’re using MySQL 5.7, which adds the JSON data type. Use JSON_EXTRACT(colname, '$.cost') to access the cost property. It will be NULL is there’s no such property.

1. WHERE JSON_EXTRACT(colname, '$.cost') IS NOT NULL
2. WHERE JSON_EXTRACT(colname, '$.cost') IS NULL
3. WHERE JSON_EXTRACT(colname, '$.cost') != ''

It will also be NULL if the value in the JSON is null; if you need to distinguish this case, see Can’t detect null value from JSON_EXTRACT