Mysqlupdate statement problems

For example, the following is a piece of SQL I wrote. why is it difficult to run during the running and cannot be executed after the time is exceeded? Updateoverseas_contract_materialsetexecutedNumexecutedNum-12wherecontractId & #39; ef556813-e5ae-e5a9-9157-f91f963ee570 & #39; andmaterialId & #39; 184 & #39; mysqlupdate

For example, the following is a piece of SQL I wrote. why is it difficult to run during the running and cannot be executed after the time is exceeded?
Update overseas_contract_material set executedNum = executedNum-12 where contractId = 'ef556813-e5ae-e5a9-9157-f91f963ee570 'and materialId = '2016 ';