Oracle数据库中查看当前用户下有多少张表的命令是( ) A. selectcount(*)fromuser-table; B. selectcount(*)fromuser_table; C. selectcount(*)fromuser-tables; D. selectcount(*)fromusertables; 相关知识点: 试题来源: 解析 C null 反馈 收藏 ...
With cnt as(select count(*) from table) Select cnt+1 from dual; 是错误的。必须是 With cnt as(select count(*) shumu from user_tables) Select shumu+1 from cnt; --直接引用with子查询中的列别名。 一个with查询的实例: 查询出部门的总薪水大于所有部门平均总薪水的部门。部门表s_dept,员工表s...
declare v_sql varchar2(2000);V_BK_TABLE varchar2(20);v_flag int;begin V_BK_TABLE:='A'; -- 给表名变量赋值V_SQL := 'SELECT COUNT(1) FROM User_Tables WHERE table_name ='||'''||V_BK_TABLE||''';EXECUTE IMMEDIATE V_SQL INTO V_FLAG;dbms_output.put_line(v_flag)...
SQL>select * from user_sys_privs; SQL>select * from user_tab_privs; 6、 查看当前用户的缺省表空间 SQL>select username,default_tablespace from user_users; 7、 查看用户下所有的表 SQL>select * from user_tables; SQL>select * from dba_tables where owner='大写用户名字'; 8、 查看用户下所有的...
前提是你的统计更新是实时的。在 Oracle 中，也有相应的字典表，比如 ALL_TABLES.
as counts 将计算结果的列命名为 counts，这样在外部查询中就可以通过这个名字来引用这个列。
mysql>SELECTCOUNT(*)FROMstudent; This optimization only applies to MyISAM tables, because an exact row count is stored for this storage engine and can be accessed very quickly.COUNT(1) is only subject to the same optimization if the first column is defined as NOT NULL. ...
Using SELECT SINGLE COL for checking the existence is fine for buffered tables, but we faced that for non-buffered tables it is even better to do SELECT SINGLE COUNT( COL ) as 1) you really don't fetch any data and 2) you don't have to define a variable, which you're not using ...
select * from pg_stat_user_tables where n_live_tup > 100000 and seq_scan > 0 order by seq_tup_read desc limit 10; 9、查询读取buffer最多的5个SQL select * from pg_stat_statements order by shared_blks_hit+shared_blks_read desc limit 5; ...
2)、Tools–>Preferences–>User Interface–>Editor–>AutoReplace,选中Enable复选框,然后浏览文件选中之前创建的shortcuts.txt,点击Apply。 3)、重启PL/SQL Developer,在sql窗口中输入s+空格,sc+空格做测试。 注意:shortcuts.txt不可删除掉,否则快捷键无法用 ...