1. strict_multi_assignment - checks the number of target variables and source values.
I've proposed this before (maybe around a year ago), except the checks were done at parse time, rather than runtime. I much prefer that approach. If I recall correctly, the patch was considered to be good, but not good enough since it didn't handle all contexts (perhaps FOR loop were missing, or something; I forget).
Please, can me send a link? Compile time check is better - but I am not sure how much increase a complexity of patch. There should not be necessary data in compile time available. You need a rewriten query - and it is not available in compile time. More in compile time you should not to check dynamic SQL.
2. too_many_rows - checks if returned rows is more than one
I've also proposed this, and it was rejected because it was a runtime check, and some people don't like runtime checks.
This runtime check is well controlled, and should be simply enabled, simply disabled - more it is almost impossible process this check in compile time.
