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Screnn clean Command:host clsSys user, dba user Unlock:alter user user_name account unlock; setting:alter user user_name identified by password;Query User: show users; update password: password;Query tables: select * from tab; sets the display column width (numeric type number), 9 indicates numeric type, a 9 represents one digit, and can only use 9 column ename format 9999 Set display column width (character type varchar2,date), 10 width bits, an indicates character type, case can be column character type format A10; set one page display record height such as 100 set pagesize 100; execute the last SQL statement using / * called wildcard, indicating that all field data dictionaries in the table remove the duplicate field select distinct user_period from user_name Use aliases with double quotes (no double quotes and no spaces). You cannot add single quotes in oracle to indicate string type or date type select sal*12 AS "annual salary" from emp; select sal*12+NVL (conn,0) from emp Operations such as +, -, *,% are supported. If the result is null, it is not displayed in the sqlplus client. The special function select NVL (null,10) from emp;Null of the liberation scheme Oracle and the specific number dual dumb table or pseudo table | | connection symbol select 'hellpw' | |' word' "result" from dual; gets the system date select now () Use the keyword in Oracle to get the select sysdate from dual; query content splicing pipe character select ename | | 'salary is' | sal | | 'USD' from emp; records the result of SQL statement (save to hard disk and create sql file) CREATE: spool user_path: oracleday 1.sql; save: spoll off; imports database @ user_path from hard disk using @ command txt.sql file Comment symbol-to represent a comment (before the SQL statement-at the front of the comment statement) / * multiline comment * /

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