TheSQLEXISTSoperatorteststheexistenceofanyvalueinasubqueryi.e.itexecutestheouterSQLqueryonlyifthesubqueryisnotNULL(emptyresult-set).
The SQL EXISTS operator tests the existence of any value in a subquery i.e. it executes the outer SQL query only if the subquery is not NULL (empty result-set).
sql exists取代inSQL EXCEPTsql exists in效率SQL NOT EXISTSSQL exist vs INsql exists in差別SQL NOT INSQLsql下載sql教學sql是什麼sql語法sql軟體sql自學sql用途sql資料庫sql exists取代in
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