Oracle sql语句执行顺序
- - 数据库 - ITeye博客sql语法的分析是从右到左. 一、sql语句的执行步骤:. 1)语法分析,分析语句的语法是否符合规范,衡量语句中各表达式的意义. 2)语义分析,检查语句中涉及的所有数据库对象是否存在,且用户有相应的权限. 3)视图转换,将涉及视图的查询语句转换为相应的对基表查询语句. 4)表达式转换, 将复杂的 SQL 表达式转换为较简单的等效连接表达式.
--查看Oracle数据库字符集: select userenv('language') from dual; ---正在执行的 select a.username, a.sid, b.SQL_TEXT, b.SQL_FULLTEXT from v$session a, v$sqlarea b where a.sql_address = b.address; ---执行过的 (此方法好处可以查看某一时间段执行过的sql,并且 SQL_FULLTEXT 包含了完整的 sql 语句) select b.SQL_TEXT, b.FIRST_LOAD_TIME, b.SQL_FULLTEXT from v$sqlarea b where b.FIRST_LOAD_TIME between '2009-10-15/09:24:47' and '2009-10-15/09:24:47' order by b.FIRST_LOAD_TIME; --其他 select OSUSER, PROGRAM, USERNAME, SCHEMANAME, B.Cpu_Time, STATUS, B.SQL_TEXT from V$SESSION A LEFT JOIN V$SQL B ON A.SQL_ADDRESS = B.ADDRESS AND A.SQL_HASH_VALUE = B.HASH_VALUE order by b.cpu_time desc; select address, sql_text, piece from v$session, v$sqltext where address = sql_address -- and machine = < you machine name > order by address, piece; -- 查找前十条性能差的sql. SELECT * FROM (select PARSING_USER_ID, EXECUTIONS, SORTS, COMMAND_TYPE, DISK_READS, sql_text FROM v$sqlarea order BY disk_reads DESC) where ROWNUM < 10; --查看占io较大的正在运行的session SELECT se.sid, se.serial#, pr.SPID, se.username, se.status, se.terminal, se.program, se.MODULE, se.sql_address, st.event, st. p1text, si.physical_reads, si.block_changes FROM v$session se, v$session_wait st, v$sess_io si, v$process pr WHERE st.sid = se.sid AND st. sid = si.sid AND se.PADDR = pr.ADDR AND se.sid > 6 AND st. wait_time = 0 AND st.event NOT LIKE '%SQL%' ORDER BY physical_reads DESC;