SQL: Parse JSON
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Using SQL, how can I select the value for "conversion_event" from the JSON below?

    {"str":[1,1173,10005,"offsite_conversion.lead",{"action.type":"offsite_conversion","conversion_event":387950188,"tag":"lead"},["conversion_event"],[],{"amount":14486},"1:11:1:0:0:1:0"]}

There are some unusual things in here, for example JSON within JSON, and the square brackets. 