SQL Association operations (Query and update)

    sql In addition to the associated query, you can also associate update deletion, and sometimes a SQL to take care of data migration,  avoid writing stored procedures. The following is a list of the various cascading operations scenarios for SQL.         Main Table: Department table-dept (Dept_id,dname,enum)        From table: Employee table-emp  (emp_id , ename , sal,dept_id)       // Here is the SQL syntax  1 for Oracle, associated queries      scenarios: Querying the department name of all employees                     2, related updates      Scenario: Number of people updating departmental tables enum           update dept d  set d.enum =               ( Select count (*)  from emp e    where e.dept_id=d.dept_id );   3, correlated subqueries      scenario A: Which employees pay-sal  higher than the average wage in the Department                scene B: IsolatedNo employee department           4, associated deletions      scenes: Delete departments without employees 

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SQL Association operations (Query and update)