Database MySQL content supplement two

Multi-table query mysql support is SQL99 standard connection query, does not support Oracle Company's external connection query, but supports Oracle equivalent query, not equivalent query, self-connection query, subquery (as long as it is not an outer join (  +  ) are supported) Oracle also supports SQL99 standard connection queries 

Internal Connection--equivalent QuerySelectE.empno,e.ename,e.sal,d.dname fromEMP Einner Join dept Don E.deptno=D.deptno;--To put it simply: replace the comma in the Oracle Multi-table query syntax with the INNER join, where the query condition is placed after on, emphasizing that on the back is not just a join condition or a query condition--non-equivalent querySelectE.empno,e.ename,e.sal,s.grade fromemp Einner join Salgrade son e.sal>=s.losal and e.sal<=s.hisal; left OUTER join (right outer join--Right join)SelectD.deptno,d.dname,count (e.empno) fromDept dleft join EMP Eon D.deptno=E.deptnogroup by D.deptno, D.dname-- LEFT OUTER JOIN note that if you want to show all the data for that table, use that table as a base table , for example, to display unit 40th in the Dept table, so dept is the base table, the Oracle (+) instead.

filter null function in MySQL --ifnull (field name, desired value)--mysql no Nvl () function

string Connection --mysql in MySQL does not support '| | ' in Oracle " connection Symbol --mysql support for concat () connection functions in Oracle

Database MySQL content supplement two