Database (Learning to organize)----4--oracle data query (base point 1)

Other: The memory in the computer is linear, one-dimensional. Length ("'count the number of characters, not the number of bytes the date type and numeric type data in Oracle can do operators (>,=,<,<>) comparison occurs when the Oracle database is started: Ora-12514 The error number of the hint. Solution: Go to Oracle install directory below to find: C:\oracle\product\10.2.0\db_1\network\admin directory below: Found: Listener.ora files and Tnsnames.ora files to modify the access rights of the file, administrator open, modify the file: Host: The corresponding data: the IP of their own computer: How to modify: LocalHost or127.0.0.1or the real IP of the current computer.1, query: Keywords can be used afterSelect*, field lists, expressions, functions, query statements fromtable name, query statement, view listwhere(before grouping) conditions Group by group have (after grouping) condition order by sort (liters, descending)2, 4 sets of fuzzy keywords in Oracle1, like, not like2、 is NULL、 isNotNULL    3, between and, not between and4、inch(A,B,C) notinch(a,b,c)3, alias: 2 Way1, Field name asexamples of aliases:SelectEname asName fromEMP; (recommended)SelectEname as "name"  fromEMP; (not recommended)2, field name aliases Example:Selectename Name fromEMP; (not recommended)4, Data splicing: splicing: Using symbols:||to splice data examples:Select 'Name:'|| ename| |', Salary:'|| Sal asEmployee Salary Information fromEMP; Results show: Employee Salary Information Name: Jason, Salary:10000Name: Jack, Salary:20000            ..... Description: (1Data stitching in Oracle and data stitching in Java: In Java: Using"+"in Oracle: Using||(2): Single quotes are used only in 2 cases:1, character-based data2, date-based data5, Sort: ORDER by ASC: Ascending desc: Descending By default is ASC ascending (1), once sorted using: Order BY field name [ASC/DESC]; or an order BY expression [ASC/DESC]; (2), two orders: use: Order BY field name 1 [ASC/DESC], field name 2 [asc/DESC]; or order By field name 1 [ASC/DESC], expression [asc/DESC]; Description: The sortable type in Oracle is only: numeric/Date Type/Character Type6, UNION query: Union Description:1, union refers to the table up and down stitching, not the column splicing! 2, using three consistent conditions: (quantity consistent, type consistent, order consistent). 3, the column name of the final displayed column is subject to the first select! Examples of use:SelectEname,sal asSalary fromScott.empwhererownum<=2UnionSelectEname asName, Sal fromscott.emp; Search Result: ename salary ADAMS1100.00ALLEN1600.00BLAKE2850.00CLARK2450.00FORD3000.00JAMES950.007, query the data for the specified number of bars: keyword: rowid the value of the row cursor, the address of the line, before traversing the current line will have a value!    RowNum a pseudo-column of the current row, (pseudo-column) is generated when the query occurs, and the end of the query is dead! Special Note: rownum: only use:< and <=, and only in:Select* fromEmpwhererownum=1In this case, you can use =Example: requirements: How to check 6-10 rows of data! SQL statements:Select* fromscott.empwhereScott.emp.empno notinch(SelectScott.emp.empno fromScott.empwhererownum<=5) and RowNum<=5; Information Extraction: Paging function:Select* fromscott.empwhereScott.emp.empno notinch(SelectScott.emp.empno fromScott.empwhererownum<= Current Page *pages per page) and RowNum<=number of bars per page;8to alias a table: The method is simple: Format: Table name alias Special Note: In the query statement, after the table alias, you can no longer use the table name, you should use the alias just taken! 

Database (Learning grooming)----4--oracle data query (base point 1)