OCP之黄伟
参考视频:
[bbk5486]第4集 - 10g OCP之007研究
[bbk5487]第5集 - 10g OCP之007研究
[bbk5488]第6集 - 10g OCP之007研究
Cluster table适合查询，因为聚簇表会将相关联的表信息数据存放在一个块中，这样读取数据时，会一次I/O读到全部信息，减少I/O,提高性能.
多表联合查询.不适合DML操作;
不适合TRUNCATE操作.不适合做全表扫描，因为你在进行I/O操作的时候，需要将相关联的、但是实际不需要的额外数据给读取出来，所以不适合全表扫描;
聚簇表，分为基于索引的和基于哈希的；
如果没有索引，是拒绝DML操作的.所以是先要进行创建索引，然后再进行DML操作.
在聚簇表中，相同的ROWID不能完全定位唯一一条记录，有可能是多条.这是聚簇表与普通heap表的区别.也就是说，在聚簇表中，表dept和表emp中拥有完全重复的rowid，是不足为奇的，不重复，就不正常了.
OCP 007课程概述
- 数据查询语言：SELECT;
- 数据定义语言：CREATE、ALTER、DROP、TRUNCATE、RENAME
- 数据修改语言：INSERT、UPDATE、DELETE、MERGE;
- 数据控制语言：GRANT、REVOKE;
- 事务控制语言：COMMIT、ROLLBACK、SAVEPOINT;
- 会话控制语言：ALTER SESSION;
- 系统控制语言：ALTER SYSTEM;
Writing SQL Statements
- SQL statements are not case-sensitive.
- SQL statements can be on one or more lines.
- Keywords cannot be abbreviated or split across lines.
- Clauses are usually placed on separate lines.
- Indents are used to enhance readability.
- In iSQL*Plus,SQL statements can optionally be terminated by a semicolon(;).Semicolons are required if you execute multiple SQL statements.
- In SQL*plus,you are required to end eac SQL statement with a semicolon(;);
Column Heading Defaults
- iSQL*Plus
- Default heading alignment:Center
- Default heading display:Uppercase
- SQL*Plus
- Character and Date column heading are Left-aligned.
- Number column headings are right-aligned.
- Default heading display:Uppercase.
Defining a Null Value
A null is a value that is unabailable,unassigned,unknown,or inapplicable.
A null is not the same as a zero or a blank space.
null value，就是没有分配内存地址，不知道，不适用的这么一个值.
null value是不能做等值比较的.只能用is null或者is not null；
注意：空值和空值是不相等的；
在唯一约束上，是允许有空值的；而且允许又多个空值.因为空值和空值是不相等的。
凡是空值参与的所有运算，最后的结果都是空值.
Defining a Column Alias
A column alias:
- Renames a column heading
- Is useful with calculations
- Immediately follows the column name(There can also be the optional AS keyword between the column name nad alias.)
- Requires double quotation marks if it contains spaces or special characters or if it is case-sensitive
- Can`t be used in Where clause
Concatenation Operator
注意：列别名中使用的是双引号，而字符串拼接使用的是单引号.
A concatenation operator:
- Links columns or character strings to other columns
- Is represented by two vertical bars(||)
- Creates a resultant column that is a character expression
SQL> select last_name || chr(39) || salary from emp; LAST_NAME||CHR(39)||SALARY ------------------------------------------------------------------ Hartstein'13000 Fay'6000 Raphaely'11000 Khoo'3100 Baida'2900 Tobias'2800 Himuro'2600 Colmenares'2500 OConnell'2600 Grant'2600 Weiss'8000 LAST_NAME||CHR(39)||SALARY ------------------------------------------------------------------ Fripp'8200 Kaufling'7900 Vollman'6500 Mourgos'5800 Nayer'3200 Mikkilineni'2700 Landry'2400 Markle'2200 Bissot'3300 Atkinson'2800 Marlow'2500 LAST_NAME||CHR(39)||SALARY ------------------------------------------------------------------ Olson'2100 Mallin'3300 Rogers'2900 Gee'2400 Philtanker'2200 Ladwig'3600 Stiles'3200 Seo'2700 Patel'2500 Rajs'3500 Davies'3100 LAST_NAME||CHR(39)||SALARY ------------------------------------------------------------------ Matos'2600 Vargas'2500 Taylor'3200 Fleaur'3100 Sullivan'2500 Geoni'2800 Sarchand'4200 Bull'4100 Dellinger'3400 Cabrio'3000 Chung'3800 LAST_NAME||CHR(39)||SALARY ------------------------------------------------------------------ Dilly'3600 Gates'2900 Perkins'2500 Bell'4000 Everett'3900 McCain'3200 Jones'2800 Walsh'3100 Feeney'3000 Mavris'6500 Whalen'4400 LAST_NAME||CHR(39)||SALARY ------------------------------------------------------------------ Higgins'12008 Gietz'8300 Hunold'9000 Ernst'6000 Austin'4800 Pataballa'4800 Lorentz'4200 Baer'10000 Russell'14000 Partners'13500 Errazuriz'12000 LAST_NAME||CHR(39)||SALARY ------------------------------------------------------------------ Cambrault'11000 Zlotkey'10500 Tucker'10000 Bernstein'9500 Hall'9000 Olsen'8000 Cambrault'7500 Tuvault'7000 King'10000 Sully'9500 McEwen'9000 LAST_NAME||CHR(39)||SALARY ------------------------------------------------------------------ Smith'8000 Doran'7500 Sewall'7000 Vishney'10500 Greene'9500 Marvins'7200 Lee'6800 Ande'6400 Banda'6200 Ozer'11500 Bloom'10000 LAST_NAME||CHR(39)||SALARY ------------------------------------------------------------------ Fox'9600 Smith'7400 Bates'7300 Kumar'6100 Abel'11000 Hutton'8800 Taylor'8600 Livingston'8400 Johnson'6200 King'24000 Kochhar'17000 LAST_NAME||CHR(39)||SALARY ------------------------------------------------------------------ De Haan'17000 Greenberg'12008 Faviet'9000 Chen'8200 Sciarra'7700 Urman'7800 Popp'6900 Grant'7000
SQL> select last_name || '''s' || salary from emp; LAST_NAME||'''S'||SALARY ------------------------------------------------------------------- Hartstein's13000 Fay's6000 Raphaely's11000 Khoo's3100 Baida's2900 Tobias's2800 Himuro's2600 Colmenares's2500 OConnell's2600 Grant's2600 Weiss's8000 LAST_NAME||'''S'||SALARY ------------------------------------------------------------------- Fripp's8200 Kaufling's7900 Vollman's6500 Mourgos's5800 Nayer's3200 Mikkilineni's2700 Landry's2400 Markle's2200 Bissot's3300 Atkinson's2800 Marlow's2500 LAST_NAME||'''S'||SALARY ------------------------------------------------------------------- Olson's2100 Mallin's3300 Rogers's2900 Gee's2400 Philtanker's2200 Ladwig's3600 Stiles's3200 Seo's2700 Patel's2500 Rajs's3500 Davies's3100 LAST_NAME||'''S'||SALARY ------------------------------------------------------------------- Matos's2600 Vargas's2500 Taylor's3200 Fleaur's3100 Sullivan's2500 Geoni's2800 Sarchand's4200 Bull's4100 Dellinger's3400 Cabrio's3000 Chung's3800 LAST_NAME||'''S'||SALARY ------------------------------------------------------------------- Dilly's3600 Gates's2900 Perkins's2500 Bell's4000 Everett's3900 McCain's3200 Jones's2800 Walsh's3100 Feeney's3000 Mavris's6500 Whalen's4400 LAST_NAME||'''S'||SALARY ------------------------------------------------------------------- Higgins's12008 Gietz's8300 Hunold's9000 Ernst's6000 Austin's4800 Pataballa's4800 Lorentz's4200 Baer's10000 Russell's14000 Partners's13500 Errazuriz's12000 LAST_NAME||'''S'||SALARY ------------------------------------------------------------------- Cambrault's11000 Zlotkey's10500 Tucker's10000 Bernstein's9500 Hall's9000 Olsen's8000 Cambrault's7500 Tuvault's7000 King's10000 Sully's9500 McEwen's9000 LAST_NAME||'''S'||SALARY ------------------------------------------------------------------- Smith's8000 Doran's7500 Sewall's7000 Vishney's10500 Greene's9500 Marvins's7200 Lee's6800 Ande's6400 Banda's6200 Ozer's11500 Bloom's10000 LAST_NAME||'''S'||SALARY ------------------------------------------------------------------- Fox's9600 Smith's7400 Bates's7300 Kumar's6100 Abel's11000 Hutton's8800 Taylor's8600 Livingston's8400 Johnson's6200 King's24000 Kochhar's17000 LAST_NAME||'''S'||SALARY ------------------------------------------------------------------- De Haan's17000 Greenberg's12008 Faviet's9000 Chen's8200 Sciarra's7700 Urman's7800 Popp's6900 Grant's7000 107 rows selected.
'''s'->解读：第一个和第四个单引号是一对，第二个单引号是转义含义，第三个单引号是真正的字符.
chr(39)含义与'''s'是相同的，都是返回的`s这个值.
Literal Character Strings
- A literal is a character,a number,or a date that is included in the SELECT statement.
- Date and character literal values must be enclosed by single quotation marks.
- Each character string is output once for each row returned.
--二者是等价的
SQL> select distinct department_id from employees; SQL> select unique department_id from employees;
在排序的过程中，如果按照带有空值的字段进行排序，默认情况下是将空值字段放在最后的；之所以将控制放在最后，是因为oracle是将空值当做无穷大来处理的.
SQL> select last_name,commission_pct from employees order by 2; LAST_NAME COMMISSION_PCT ------------------------- -------------- Lee .1 Johnson .1 Marvins .1 Banda .1 Kumar .1 Ande .1 Greene .15 Grant .15 Tuvault .15 Bates .15 Smith .15 LAST_NAME COMMISSION_PCT ------------------------- -------------- Taylor .2 Bloom .2 Fox .2 Cambrault .2 Livingston .2 Zlotkey .2 Olsen .2 Sewall .25 Hall .25 Bernstein .25 Vishney .25 LAST_NAME COMMISSION_PCT ------------------------- -------------- Hutton .25 Ozer .25 Abel .3 Smith .3 Partners .3 Errazuriz .3 Tucker .3 Cambrault .3 Doran .3 King .35 Sully .35 LAST_NAME COMMISSION_PCT ------------------------- -------------- McEwen .35 Russell .4 OConnell Grant Whalen Hartstein Fay Mavris Baer Higgins Gietz LAST_NAME COMMISSION_PCT ------------------------- -------------- King Kochhar De Haan Hunold Ernst Austin Pataballa Lorentz Greenberg Faviet Chen LAST_NAME COMMISSION_PCT ------------------------- -------------- Sciarra Urman Popp Raphaely Khoo Baida Tobias Himuro Colmenares Weiss Fripp LAST_NAME COMMISSION_PCT ------------------------- -------------- Kaufling Vollman Mourgos Nayer Mikkilineni Landry Markle Bissot Atkinson Marlow Olson LAST_NAME COMMISSION_PCT ------------------------- -------------- Mallin Rogers Gee Philtanker Ladwig Stiles Seo Patel Rajs Davies Matos LAST_NAME COMMISSION_PCT ------------------------- -------------- Vargas Taylor Fleaur Sullivan Geoni Sarchand Bull Dellinger Cabrio Chung Dilly LAST_NAME COMMISSION_PCT ------------------------- -------------- Gates Perkins Bell Everett McCain Jones Walsh Feeney 107 rows selected.
假如想将控制字段排序时，放在前面可以在order by 子句后面添加关键字nulls first;想将空值放在最后，就将nulls first改为nulls last;
SQL> select last_name,commission_pct from employees order by 2 nulls first; LAST_NAME COMMISSION_PCT ------------------------- -------------- OConnell Grant Whalen Hartstein Fay Mavris Baer Higgins Gietz King Kochhar LAST_NAME COMMISSION_PCT ------------------------- -------------- De Haan Hunold Ernst Austin Pataballa Lorentz Greenberg Faviet Chen Sciarra Urman LAST_NAME COMMISSION_PCT ------------------------- -------------- Popp Raphaely Khoo Baida Tobias Himuro Colmenares Weiss Fripp Kaufling Vollman LAST_NAME COMMISSION_PCT ------------------------- -------------- Mourgos Nayer Mikkilineni Landry Markle Bissot Atkinson Marlow Olson Mallin Rogers LAST_NAME COMMISSION_PCT ------------------------- -------------- Gee Philtanker Ladwig Stiles Seo Patel Rajs Davies Matos Vargas Taylor LAST_NAME COMMISSION_PCT ------------------------- -------------- Fleaur Sullivan Geoni Sarchand Bull Dellinger Cabrio Chung Dilly Gates Perkins LAST_NAME COMMISSION_PCT ------------------------- -------------- Bell Everett McCain Jones Walsh Feeney Lee .1 Johnson .1 Marvins .1 Banda .1 Kumar .1 LAST_NAME COMMISSION_PCT ------------------------- -------------- Ande .1 Greene .15 Grant .15 Tuvault .15 Bates .15 Smith .15 Taylor .2 Bloom .2 Fox .2 Cambrault .2 Livingston .2 LAST_NAME COMMISSION_PCT ------------------------- -------------- Zlotkey .2 Olsen .2 Sewall .25 Hall .25 Bernstein .25 Vishney .25 Hutton .25 Ozer .25 Abel .3 Smith .3 Partners .3 LAST_NAME COMMISSION_PCT ------------------------- -------------- Errazuriz .3 Tucker .3 Cambrault .3 Doran .3 King .35 Sully .35 McEwen .35 Russell .4 107 rows selected.
SQL statements Versus iSQL*Plus Commands
| SQL | iSQL*Plus |
| A language | An enviromnet |
| ANSI standard | Oracle-proprietary |
| Keyword cannot be abbreviated | Keywords can be abbreviated |
| Statements manipulate data and table definitions in the database | Commands do not allow manipulation of values in the database |
| Runs on a browser | |
| Centrally loaded;does not have to be implemented on each machine | |
| SQL statements | iSQL*Plus commands |
Summary
In this lesson,you should be have learned how to:
- Write a SELECT statement that:
- Returns all rows and columns from a table.
- Returns specified columns from a table.
- Uses column aliases to display more descriptive column headings
- Use the iSQL*Plus enviroments to write,save,and execute SQL statements and iSQL*Plus command.
SELECT *|{[DISTINCT] column|expression [alias],...} FROM table;
