一起合同网

⬬ 抓住关键字眼作文 ⬬

《匆匆》这篇课文在上周的星期五进行了第三次研讨，由刘莉老师执教。总的来说，刘莉老师从钻研教材、把握重难点、确定教法上就前面两位老师更突显了自己思考的痕迹。40分钟下来，可圈可点的地方有很多，我也从中获益匪浅。

一、开课由词语入手，梳理文中重要线索。老师通过引导学生读两组重点词，从而帮助学生理清文章两条重要的线索，其一是描写时间的流逝，一去不复返；其二是作者面对时间的流逝内心的感叹。但老师接下来提问：“默读课文，思考文中哪些词说明时间匆匆，一去不复返，并进行简单的批注。①”我想刘老师所要表达的意图是很清晰的，就是从词语入手引导学生走进文本去深入地理解体会作者的情感。但就小学高段在阅读教学中追问或提问的语言组织该如何引导学生真正走进文本，真正实现课堂实效的延伸呢？我觉得这个问题，值得我们作进一步的思考。

二、接着刘老师引导学生围绕刚才所提出的问题①进行了逐段的理解与体会。四段讲解下来，平均用力，中心点不够明确。这是一篇散文，正所谓“形散而神不散”，那这篇文章的中心点该是什么？“我不禁头涔涔而泪潸潸了。”文中的这句话虽是描写作者面对时间流逝的感受，但如果在开课读完词以后，直接提出“头涔涔”和“泪潸潸”来理解，并围绕这两个词老师进行追问：“为什么作者会头涔涔而泪潸潸？”我想这个问题更能引导学生有效地走进文本，学生会马上提出是因为时间去得匆匆，并且一去不复返。老师进一步追问：“从文章中的哪些词句可以感受到时间的匆匆和一去不复返？”学生再次深入走进文本，去抓文章中的关键词句品读体会。这个问题关键在于课文的1——3自然段，作者分别用了比喻、排比等修辞手法来表现，这是写作中的一个亮点，也是从学到习的一个重点。刘老师在这里抓出了每个自然段的关键之处和学生一起理解、探讨以及朗读，并且读写结合，将写作方法和语言的'训练落实到笔头上，增强了这堂课的时效性。但需要注意的是这三段文字虽然都是在描写时间的匆匆和一去不复返，但是作者的情感却是层层深入，从面对时间流逝的无奈，到认为自己无所作为的后悔、惋惜和自责，我想我们在教学的过程中，可以通过理解去体会这种情感，也可以回扣前面的“头涔涔和泪潸潸”使这种情感在读者（学生）的心中得到提升。也正是因为“头涔涔”“泪潸潸”，才有了作者经过无奈、后悔、自责后的豁然开朗，也才有了作者的这种不懈追求，也就是四自然段中一连串的追问，这也是文章的一个高潮。教师在教学中，应抓住文章中的关键点，用它来引领全文，引导学生层层深入地理解体会。

⬬ 抓住关键字眼作文 ⬬

1、到了五升六的时候，我感觉是孩子学习最关键的时期，因为以前所学的东西马上就要体现为真正的果实了，所以一定要加倍努力，尤其是暑期时间，一定要充分利用，现在想起来，我们在五升六暑期的学习对于成绩的提升简直太关键了！

2、到了这个时间，作为家长一定要根据孩子的学习情况制定一个切实可行的`方案。坑不在多，但是也不能只占一个坑，总要给自己留条备选的路。确定一个主攻目标，同时再有一个备选的就够了，这样也不会让孩子课程太多，无所适从。换句话，从开始的时候心里就要有数：我最理想的是去哪里，发挥一般能去哪里，发挥失常，最差也能去哪里，有了这些，就不再盲目。

3、好象今年有不少家长都埋怨培训机构没有提供参加名校考试的机会等等，其实想起来很大程度上是家长自身的责任。一方面先期选拔考试准备不足，或者孩子自身的实力不够，或者家长没有充分关注考试的动态，阴差阳错与机会失之交臂。所以作为家长一定要随时关注目标学校的考试动态，机会总是给有准备的人。

4、虽然说现在是奥数当家的时代，但是平时还是尽可能让孩子保持全面发展，知识是平时积累的，尤其从今年的面试来看，很大程度上你是无从准备的，就是孩子的知识面和语言表达能力的真实体现。最重要的是，不是全部，全面发展的孩子在中学阶段才更有理由继续保持领先。

5、到任何时候都要把提升孩子的学习实力放在首要位置。

6、搞清楚所在区的政策，如果因为这方面原因导致失败，不能不说是家长的失职啊，到时候后悔晚矣！

⬬ 抓住关键字眼作文 ⬬

苹果从树上掉下来，是一件司空见惯的事。可牛顿却能从这么一件极其普通的事情中发现万有引力，这就是成功。也许你会常常抱怨，苹果为何不砸在你头上。可是，你想过没有，如果真的有那么一天，你是会产生疑问，还是一口将苹果吃掉;是会发现科学奥妙，还是气不过将那苹果用力往下一扔?苹果是一个机遇。牛顿拿起苹果产生疑问后进行探索，他就抓住了机遇;而你，却将这个苹果抓在手中又毫不犹豫地扔掉，你就错过了机遇。

无独有偶。1973年，一位叫柯莱特的青年考入了哈佛大学，常和他一起听课的是一位18岁的美国小伙子。这个小伙子大学没毕业便毅然离开学校，开创了自己的计算机公司。当他邀请柯莱特加入时，柯莱特拒绝了，表示要在完成学业后再创建自己的事业。可等到柯莱特毕业时，那位小伙子却已经成为了世界首富。他就是比尔·盖茨。对于柯莱特来说，比尔·盖茨的邀请是一个机遇，可他错过了。对于比尔·盖茨来说，他的决定——离开学校创建事业就是机遇，他抓住了。

我们每个人身边都有机遇。

二年级时，我从乡下转入实验小学。在我入学的第三天，班主任唐老师因为我字写得好而推荐我当了班长，这可是我梦寐以求的啊。从此，平凡的我成了老师的好帮手。我时刻告诫自己，努力学习，严于律己，当好同学们的表率。直到今天，我仍胜任着这一光荣的职责。我一直在想，那次的机遇是什么?是因为遇到了唐老师?不管是什么，我知道我抓住了机遇。

⬬ 抓住关键字眼作文 ⬬

ROWNUM：

说明：rownum是一个伪字段，标示查询字段的序号;

注意：

select * from emp where rownum>3、

原因：rownum是在使用select查询的时候，自动生成的一串顺序号，

当select 一条数据 rownum 为 1 不>3 记录被筛去

而下一条 数据 rownum 又是 1.。。。。。。。

rownum 是不支持order by 排序的。因为rownum是在排序之前取值的。

“在oracle中如果rownum与order by同在，是先rownum，然后再order by ”

oracle手册上说的：“即使select语句中一条简单的order by都可能会搞乱ROWNUM(因为ROWNUM是排序前分配给各行的)

解决方式：

1、直接嵌套：(增加了两次查询，被嵌套的查询结果相当于视图，view中已经有rownum字段 所以可以使用 > 号)

select t1.*,ROWNUM rn from (--解决order by 的影响

k.bmxh,

k.byxxdm,

z.zgdm,

z.dqdm,

left join ks k on z.bmxh = k.bmxh

left join zgdm zd on z.zgdm = zd.zgdm

)t2where rn > 2 and rn <10

2、使用：row_number over(order by COLUMN_NAME) 改变顺序，先执行了括号中的order by

select z.* ,row_number() over ( order by z.bmxh ) rn from zgjf z where rownum <10 and rownum >5

⬬ 抓住关键字眼作文 ⬬

Working with Strings（使用Oracle字符串）

Part 3 in a series of articles on understanding and using PL/SQL

Every application needs data. That seems rather obvious, doesn’t it? An application is almost always built on top of database tables. Those tables are full of different kinds of data. And the programs you write—whether they are in PL/SQL or another language—manipulate that data. It is, therefore, extremely important for you to be aware of the different datatypes supported by PL/SQL and how you can work with those datatypes.

Take the Challenge!

Each of my PL/SQL 101 articles offers a quiz to test your knowledge of the information provided in the article. The quiz questions are shown below and also at PL/SQL Challenge (), a Website that offers online quizzes for the PL/SQL language. You can read and answer the quiz here, and then check your answers in the next issue. If, however, you take the quiz at PL/SQL Challenge, you will be entered into a raffle to win your choice of an e-book from O’Reilly Media ().

What will be displayed after executing this block?

sys.DBMS_OUTPUT.put_line (

INSTR ('steven feuerstein'

, 2));

True or false: When assigning a literal value to a string, that value may not contain within it any single quotes.

What will be displayed after executing this block?

DBMS_OUTPUT.put_line (

'REPLACE='

|| REPLACE ('steven feuerstein'

, 'e'

, NULL));

DBMS_OUTPUT.put_line (

'TRANSLATE='

|| TRANSLATE ('steven feuerstein'

, 'e'

, NULL));

END;

As you might expect, there is an awful lot to learn about datatypes, and not all of that knowledge can fit into a single article. So I will start with one of the most common types of data: strings. Very few database tables and programs do not contain strings—strings such as a company name, address information, descriptive text, and so on. As a result, you quite often need to do the following:

Declare string variables and constants

Manipulate the contents of a string (remove characters, join together multiple strings, and so on)

Move string data between PL/SQL programs and database tables

This article gives you the information you need to begin working with strings in your PL/SQL programs.

What Is a String?

A string, also referred to as character data, is a sequence of selected symbols from a particular set of characters. In other words, the symbols in a string might consist of English letters, such as ”A” or ”B.” They might also consist of Chinese characters, such as 字串.

There are three kinds of strings in PL/SQL:

Fixed-length strings. The string is right-padded with spaces to the length specified in the declaration. (See ”Declaring String Variables,” to see padding in action.)

Variable-length strings. A maximum length for the string is specified (and it must be no greater than 32,767), but no padding takes place.

Character large objects (CLOBs).CLOBs are variable-length strings that can be up to 128 terabytes.

Strings can be literals or variables. A string literal begins and ends with a single quotation mark:

'This is a string literal'

If you need to embed a single quote inside a string literal, you can type in two single quotes right next to one another, as in:

'This isn''t a date'

You can also use the “q” character to indicate an alternative terminating character for the literal:

q'[This isn't a date]'

A string variable is an identifier declared with a string datatype and then assigned a value (which could be a literal or an expression).

To work with strings in your PL/SQL programs, you declare variables to hold the string values. To declare a string variable, you must select from one of the many string datatypes Oracle Database offers, including CHAR, NCHAR, VARCHAR2, NVARCHAR2, CLOB, and NCLOB. The datatypes that are prefixed with an ”N” are “national character set” datatypes, which means they are used to store Unicode character data. (Unicode is a universal encoded character set that can store information in any language using a single character set.)

To declare a variable-length string, you must provide the maximum length of that string. The following code declares a variable, using the VARCHAR2 datatype, that will hold a company name, which cannot (in this declaration) have more than 100 characters:

l_company_name VARCHAR2(100);

You must provide the maximum length; if you leave it out, Oracle Database raises a compile error, as shown below:

2  l_company_name VARCHAR2;

'Oracle Corporation';

5 END;

6 /

l_company_name VARCHAR2;

*

ERROR at line 2:

PLS-00215: String length constraints

To declare a fixed-length string, use the CHAR datatype:

With CHAR (unlike with VARCHAR2) you do not have to specify a maximum length for a fixed-length variable. If you leave off the length constraint, Oracle Database automatically uses a maximum length of 1. In other words, the two declarations below are identical:

l_yes_or_no1 CHAR(1) := 'Y';

If you declare a CHAR variable with a length greater than 1, Oracle Database automatically pads whatever value you assign to that variable with spaces to the maximum length specified.

Finally, to declare a character large object, use the CLOB datatype. You do not specify a maximum length; the length is determined automatically by Oracle Database and is based on the database block size. Here is an example:

l_lots_of_text CLOB;

So, how do you determine which datatype to use in your programs? Here are some guidelines:

If your string might contain more than 32,767 characters, use the CLOB (or NCLOB) datatype.

If the value assigned to a string always has a fixed length (such as a U.S. Social Security number, which always has the same format and length, NNN-NN-NNNN), use CHAR (or NCHAR).

Otherwise (and, therefore, most of the time), use the VARCHAR2 datatype (or NVACHAR2, when working with Unicode data).

Using the CHAR datatype for anything but strings that always have a fixed number of characters can lead to unexpected and undesirable results. Consider the following block, which mixes variable and fixed-length strings:

l_variable VARCHAR2 (10) := 'Logic';

DBMS_OUTPUT.put_line ('Equal');

DBMS_OUTPUT.put_line ('Not Equal');

END IF;

END;

At first glance, you would expect that the word “Equal” would be displayed after execution. That is not the case. Instead, “Not Equal” is displayed, because the value of l_fixed has been padded to a length of 10 with spaces. Consider the padding demonstrated in the following block; you would expect the block to display “Not Equal”:

IF 'Logic' = 'Logic  '

DBMS_OUTPUT.put_line ('Equal');

DBMS_OUTPUT.put_line ('Not Equal');

END IF;

END;

You should, as a result, be very careful about the use of the CHAR datatype, whether as the type of a variable, database column, or parameter.

Once you have declared a variable, you can assign it a value, change its value, and perform. operations on the string contained in that variable using string functions and operators.

For the rest of this article, I focus on the VARCHAR2 datatype.

Using Built-in Functions with Strings

Once you assign a string to a variable, you most likely need to analyze the contents of that string, change its value in some way, or combine it with other strings. Oracle Database offers a wide array of built-in functions to help you with all such requirements. Let’s take a look at the most commonly used of these functions.

Concatenate multiple strings. One of the most basic and frequently needed operations on strings is to combine or concatenate them together. PL/SQL offers two ways to do this:

The CONCAT function accepts two strings as its arguments and returns those two strings “stuck together.” The concatenation operator also concatenates together two strings, but it is easier to use when combining more than two strings, as you can see in this example:

l_first VARCHAR2 (10) := 'Steven';

l_middle VARCHAR2 (5) := 'Eric';

/* Use the CONCAT function */

DBMS_OUTPUT.put_line (

CONCAT ('Steven', 'Feuerstein'));

/* Use the || operator */

DBMS_OUTPUT.put_line (

|| ' '

|| l_last);

END;

/

The output from this block is:

In my experience, you rarely encounter the CONCAT function. Instead, the || operator is almost universally used by PL/SQL developers.

If either of the strings passed to CONCAT or || is NULL or ‘’ (a zero-length string), both the function and the operator simply return the non-NULL string. If both strings are NULL, NULL is returned.

Change the case of a string. Three built-in functions change the case of characters in a string:

UPPER changes all characters to uppercase.

LOWER changes all characters to lowercase.

INITCAP changes the first character of each word to uppercase (characters are delimited by a white space or non-alphanumeric character).

Listing 1 shows some examples that use these case-changing functions.

Code Listing 1: Examples of case-changing functions

2  l_company_name VARCHAR2 (25) := 'oraCLE corporatION';

4  DBMS_OUTPUT.put_line (UPPER (l_company_name));

5  DBMS_OUTPUT.put_line (LOWER (l_company_name));

6  DBMS_OUTPUT.put_line (INITCAP (l_company_name));

7 END;

Extract part of a string. One of the most commonly utilized built-in functions for strings is SUBSTR, which is used to extract a substring from a string. When calling SUBSTR, you provide the string, the position at which the desired substring starts, and the number of characters in the substring.

Listing 2 shows some examples that use the SUBSTR function.

Code Listing 2: Examples of SUBSTR function

l_company_name VARCHAR2 (6) := 'Oracle';

/* Retrieve the first character in the string */

DBMS_OUTPUT.put_line (

SUBSTR (l_company_name, 1, 1));

/* Retrieve the last character in the string */

DBMS_OUTPUT.put_line (

SUBSTR (l_company_name, -1, 1));

/* Retrieve three characters,

starting from the second position. */

DBMS_OUTPUT.put_line (

SUBSTR (l_company_name, 2, 3));

/* Retrieve the remainder of the string,

starting from the second position. */

DBMS_OUTPUT.put_line (

SUBSTR (l_company_name, 2));

END;

/

The output from this block is:

As you can see, with the SUBSTR function you can specify a negative starting position for the substring, in which case Oracle Database counts backward from the end of the string. If you do not provide a third argument—the number of characters in the substring—Oracle Database automatically returns the remainder of the string from the specified position.

Find a string within another string. Use the INSTR function to determine where (and if) a string appears within another string. INSTR accepts as many as four arguments:

The string to be searched (required).

The substring of interest (required).

The starting position of the search (optional). If the value is negative, count from the end of the string. If no value is provided, Oracle Database starts at the beginning of the string; that is, the starting position is 1.

The Nth occurrence of the substring (optional). If no value is provided, Oracle Database looks for the first occurrence.

Listing 3 shows some examples that use the INSTR function.

Code Listing 3: Examples of INSTR function

/* Find the location of the first “e” */

DBMS_OUTPUT.put_line (

INSTR ('steven feuerstein', 'e'));

/* Find the location of the first “e” starting from position 6 */

DBMS_OUTPUT.put_line (

INSTR ('steven feuerstein'

, 'e'

, 6));

/* Find the location of the first “e” starting from the 6th position from

the end of string and counting to the left. */

DBMS_OUTPUT.put_line (

INSTR ('steven feuerstein'

, 'e'

, -6));

/* Find the location of the 3rd “e” starting from the 6th position from

the end of string. */

DBMS_OUTPUT.put_line (

INSTR ('steven feuerstein'

, 3));

END;

/

The output from this block is:

INSTR is a very flexible and handy utility. It can easily be used to determine whether or not a substring appears at all in a string. Here is a Boolean function that does just that:

is_in_string (

, substring_in) > 0;

END is_in_string;

/

Pad a string with spaces (or other characters). I warned earlier about using the CHAR datatype, because Oracle Database pads your string value with spaces to the maximum length specified in the declaration.

However, there are times, primarily when generating reports, when you want to put spaces (or other characters) in front of or after the end of your string. For these situations, Oracle Database offers LPAD and RPAD.

When you call these functions, you specify the length to which you want your string padded and with what character or characters. If you do not specify any pad characters, Oracle Database defaults to padding with spaces.

Listing 4 shows some examples that use these LPAD and RPAD padding functions.

Code Listing 4: Examples of padding functions

l_first VARCHAR2 (10) := 'Steven';

l_last  VARCHAR2 (20) := 'Feuerstein';

l_phone VARCHAR2 (20) := '773-426-9093';

/* Indent the subheader by 3 characters */

DBMS_OUTPUT.put_line ('Header');

DBMS_OUTPUT.put_line (

LPAD ('Sub-header', 13, '.'));

/* Add “123” to the end of the string, until the 20 character is reached.*/

DBMS_OUTPUT.put_line (

RPAD ('abc', 20, '123'));

/* Display headers and then values to fit within the columns. */

DBMS_OUTPUT.put_line (

/*1234567890x12345678901234567890x*/

'First Name Last Name      Phone');

DBMS_OUTPUT.put_line (

|| ' '

|| ' '

|| l_phone);

END;

/

The output from this block is:

Steven  Feuerstein     773-426-9093

Replace characters in a string. Oracle Database provides a number of functions that allow you to selectively change one or more characters in a string. You might need, for example, to replace all spaces in a string with the HTML equivalent (“ ”) so the text is displayed properly in a browser. Two functions take care of such needs for you:

REPLACE replaces a set or pattern of characters with another set.

TRANSLATE translates or replaces individual characters.

Listing 5 shows some examples of these two character-replacement built-in functions. Notice that when you are replacing a single character, the effect of REPLACE and TRANSLATE is the same. When replacing multiple characters, REPLACE and TRANSLATE act differently. The call to REPLACE asked that appearances of “abc” be replaced with “123.” If, however, any of the individual characters (a, b, or c) appeared in the string outside of this pattern (“abc”), they would not be replaced.

Code Listing 5: Examples of character replacement functions

l_name VARCHAR2 (50) := 'Steven Feuerstein';

/* Replace all e's with the number 2. Since you are replacing a single

character, you can use either REPLACE or TRANSLATE. */

DBMS_OUTPUT.put_line (

REPLACE (l_name, 'e', '2'));

DBMS_OUTPUT.put_line (

TRANSLATE (l_name, 'e', '2'));

/* Replace all instances of “abc” with “123” */

DBMS_OUTPUT.put_line (

REPLACE ('abc-a-b-c-abc'

, 'abc'

, '123'));

/* Replace “a” with “1”, “b” with “2”, “c” with “3”. */

DBMS_OUTPUT.put_line (

TRANSLATE ('abc-a-b-c-abc'

, 'abc'

, '123'));

END;

/

The output from this block is:

The call to TRANSLATE, however, specified that any occurrence of each of the individual characters be replaced with the character in the third argument in the same position.

Generally, you should use REPLACE whenever you need to replace a pattern of characters, while TRANSLATE is best applied to situations in which you need to replace or substitute individual characters in the string.

Remove characters from a string. What LPAD and RPAD giveth, TRIM, LTRIM, and RTRIM taketh away. Use these trim functions to remove characters from either the beginning (left) or end (right) of the string. Listing 6 shows an example of both RTRIM and LTRIM.

Code Listing 6: Examples of LTRIM and RTRIM functions

:= 'This sentence has too many periods....';

DBMS_OUTPUT.put_line (

RTRIM (a, '.'));

DBMS_OUTPUT.put_line (

, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ '

|| 'abcdefghijklmnopqrstuvwxyz'));

END;

The output from this block is:

This sentence has too many periods

1

RTRIM removed all the periods, because the second argument specifies the character (or characters) to trim, in this case, a period. The call to LTRIM demonstrates that you can specify multiple characters to trim. In this case, I asked that all letters and spaces be trimmed from the beginning of string b, and I got what I asked for.

The default behavior. of both RTRIM and LTRIM is to trim spaces from the beginning or end of the string. Specifying RTRIM(a) is the same as asking for RTRIM(a,’ ‘). The same goes for LTRIM(a) and LTRIM(a,’ ‘).

The other trimming function is just plain TRIM. TRIM works a bit differently from LTRIM and RTRIM, as you can see in this block:

:= '.....Hi there!.....';

DBMS_OUTPUT.put_line (

TRIM (LEADING '.' FROM x));

DBMS_OUTPUT.put_line (

TRIM (TRAILING '.' FROM x));

DBMS_OUTPUT.put_line (

TRIM (BOTH '.' FROM x));

DBMS_OUTPUT.put_line (

TRIM ('.' FROM x));

--is the space:

DBMS_OUTPUT.put_line (TRIM (x));

END;

The output from this block is:

Hi there!.....

.....Hi there!

Hi there!

Hi there!

.....Hi there!.....

With TRIM, you can trim from either side or from both sides. However, you can specify only a single character to remove. You cannot, for example, write the following:

If you need to remove more than one character from the front and back of a string, you need to use RTRIM and LTRIM:

You can also use TRANSLATE to remove characters from a string by replacing them with (or “translating” them into) NULL. You must, however, take care with how you specify this replacement. Suppose I want to remove all digits (0 through 9) from a string. My first attempt yields the following block:

from the string. */

DBMS_OUTPUT.put_line (

TRANSLATE ('S1t2e3v4e56n'

, '1234567890'

, ''));

END;

/

When I execute this block, however, nothing (well, a NULL string) is displayed. This happens because if any of the arguments passed to TRANSLATE are NULL (or a zero-length string), the function returns a NULL value.

So all three arguments must be non-NULL, which means that you need to put at the start of the second and third arguments a character that will simply be replaced with itself, as in the following:

from the string. */

DBMS_OUTPUT.put_line (

一起合同网必读宝典:
• 抓住幸福作文 | 分享的作文 | 作文素材大全十篇 | 以分享为话题的作文 | 抓住关键字眼作文 | 抓住关键字眼作文

TRANSLATE ('S1t2e3v4e56n'

, 'A1234567890'

, 'A'));

END;

/

Now, “A” is replaced with “A” and the remaining characters in the string are replaced with NULL, so the string “Steven” is then displayed.

Beyond awareness of the basic properties of strings in PL/SQL and built-in functions, you can benefit by keeping the following points about long strings and maximum string sizes in mind.

When the string is too long. You must specify a maximum length when you declare a variable based on the VARCHAR2 type. What happens, then, when you try to assign a value to that variable whose length is greater than the maximum? Oracle Database raises the ORA-06502 error, which is also defined in PL/SQL as the VALUE_ERROR exception.

Here is an example of the exception being raised and propagated out of the block unhandled:

2  l_name VARCHAR2(3);

ERROR at line 1:

error: character string buffer too small

Here is a rewrite of the same block that traps the VALUE_ERROR exception:

2  l_name VARCHAR2 (3);

8   DBMS_OUTPUT.put_line (

9    'Value too large!');

10 END;

11 /

Value too large!

Interestingly, if you try to insert or update a value in a VARCHAR2 column of a database table, Oracle Database raises adifferent error, which you can see below:

SQL> CREATE TABLE small_varchar2

2 (

5 /

Table created.

3     VALUES ('abc');

*

ERROR at line 1:

ORA-12899: value too large for column

“HR”.“SMALL_VARCHAR2”.“STRING_VALUE”

Different maximum sizes. There are a number of differences between SQL and PL/SQL for the maximum sizes for string datatypes. In PL/SQL, the maximum size for VARCHAR2 is 32,767 bytes, while in SQL the maximum is 4,000 bytes. In PL/SQL, the maximum size for CHAR is 32,767 bytes, while in SQL the maximum is 2,000 bytes.

Therefore, if you need to save a value from a VARCHAR2 variable in the column of a table, you might encounter the ORA-12899 error. If this happens, you have two choices:

Use SUBSTR to extract no more than 4,000 bytes from the larger string, and save that substring to the table. This option clearly has a drawback: you lose some of your data.

Change the datatype of the column from VARCHAR2 to CLOB. This way, you can save all your data.

In PL/SQL, the maximum size for CLOB is 128 terabytes, while in SQL the maximum is just (4 GB - 1) * DB_BLOCK_SIZE.

There’s More to Data than Strings

Character data plays a very large role in PL/SQL applications, but those same applications undoubtedly also rely on data of other types, especially numbers and dates. I will cover these datatypes in the next PL/SQL 101 article.

-------------------------------

present by dylan.

⬬ 抓住关键字眼作文 ⬬

有的同学总是非常害怕写作文。每次语文老师布置作文的时候，头就开始疼了，真正写起来时，东拉一句，西扯一句，还是凑不齐。实在没办法了，只能找一些作文参考书这边一段那边一段的抄着，最后还是觉得抄也没抄好。

那么怎样才能把写作当成一种快乐?

首先，要调整心态，从心理上消除这种恐惧感。一个人进入社会就会深切体会到语言的表达对于一个人而言是多么的重要!同学们现在虽然不能亲身体会到这一点，但是在平时的阅读中一定也能感觉到，生硬而平淡无奇的文字读起来索然无味，而语句不通、表意不明的句子简直就是一堆垃圾了。作文实际上就是一个遣词造句、表情达意的过程，堂堂一个中国人，总不能连自己的语言都用不通顺吧?写作文不是为了考试，也不是为了成名成家，它就是在表达你个人的意思、意见、情感，是将思维转化成文字的过程。难道这也让你觉得害怕吗?所以，同学们在心理上还是要有一个正确的倾向：写作文是在表达自我，不是一项任务。可能有的同学会说：“我没什么好写的，无话可说。”事实是这样的吗?是真的没什么要告诉别人，还是自己找不到写作的感觉?或者是理不清自己的头绪?所以说，很多时候不是没东西写，不是没话说，而是自己够不够主动的问题。

其次，培养自己的表达欲望与写作兴趣。有一句话叫“兴趣是最好的老师”，对一件事有了兴趣，就会主动去做，并不断寻求最好的方式去做。那些喜欢写作的人，他们的文章写得好，兴趣起了很大的导引作用。主动一点，勤快一点，写作绝对不会再像你想像中的那么难，不信你试试看!

写作是在平时生活积累的基础上进行的，这种积累不仅仅在观察生活，还包括思考生活及用笔去记录生活。光去看、去发现还是不够的，更重要的是要对所闻所见形成自己的认识，并能用文字记录下来。写日记就是一个很好的习惯，一方面提高你的主动性，另一方面又锻炼了你的思维，真正写作文时就不会再感到为难了。日记是在积累一种经验、一种习惯，你平常所记的东西，可以经常拿出来翻看，作文素材自然就增加了，哪里还需要故意去生活里找?日记其实就是小作文，是自己的作文，思想、言论、事件，甚至想像的东西都可以写进去。课堂上或考试中的写作尽管有限制、有要求，但毕竟不会脱离生活，只要平时做个有人，写起来就不会觉得无话可说了。

另外，要想写好作文最为关键的一点就是多读书。读一些经典的名作，读得多了，你就会有写的冲动。尽管刚开始的时候你写得不好，但只要你坚持多读书，特别是碰到一些比较优美的词(诗)句，肯定会引起你心灵的共鸣，尽量把它们记下来，在以后的写作中你就能派上用场。

⬬ 抓住关键字眼作文 ⬬

对于一个网站的优化其最终目的是能够为网站带来流量，提升流量的转化率至使公司盈利，这是每个企业公司或个人做网站的终极目标。那么该如何才能为网站带来流量提高转化率呢?这是每站长在对一个网站优化之前都必须要考虑的问题，但是对于一些新手站长来说由于刚刚进入SEO行业其经验有很多的不足，可能对这一问题的分析研究有不够透彻的地方，于此笔者就结合多年从事SEO的实战经验以及笔者当前所优化关于销售“咖啡机”的一个站点来作为例举，为广大新手站长解析为何说长尾关键字研究分析是网站流量的主要来源?

对于关键字的研究分析笔者就在之前的一篇文章专门撰写了题为在此笔者就不专门再次详细来与大家分享如何研究分析关键字了，如果感兴趣的一些新手站长可以去看下，内容基本上是属于干货，对于如何进行关键字的分析研究做了详细的'阐述。好了话不多说了，还是言归正传吧，在笔者看来做好关键字的分析研究，一般是对长尾关键字的分析与挖掘，在对长尾关键字分析研究时可以借助专业的关键字挖掘工具，如果所优化的站点同时也在做百度竞价的话，还可以通过百度竞价词库来挖掘相关的长尾关键字，而在笔者经常对于关键字研究分析时经常使用的是百度搜索下拉框以及百度相关搜索，像这样的长尾关键字不仅仅相关性极强而且还是用户时常到搜素的词其效果很显著。笔者还有一个对长尾关键字研究的方法就是站在用户的角度去思考，通过对于用户的搜索行为以及搜索心理来分析研究长尾关键字，如：笔者当前所优化的咖啡机网站，一般来购买咖啡机的用户最为关注的是机器的价格品牌，机器的品质性能，机器的售后服务等，还有一个就是区域性的关键字，笔者公司在深圳，主要为深圳地区服务那么就可以将长尾关键字写为“深圳咖啡机”或深圳咖啡机价格等对于关键字的分析研究笔者就简单的谈到这里。

关键字的研究分析主要就是对长尾关键字的研究，以上笔者也简单的分享了如何进行长尾关键字分析，谈到长尾关键字可能有的新手站长会说，像这样的关键字搜索量非常低，而不像一些主关键字那样搜索的人高，所以有的新手站长把精力全部放在了主关键字上面去做优化想从主关键字获取流量，其结果可想而知不仅仅浪费了很大的精力和时间，该主关键字也没有做好，长尾关键字也没有做好。其实只要有点经验的站长都明白主关键字需指数很高，但是这样的词是一个很泛的词，其转化率是非常低的，不是精准流量的来源，而且竞争力非常大。就如笔者优化的咖啡机网站中的“咖啡机”这个关键字，需排名在首页的很不稳定但是基本能保持到第二页如下图：

像这样的主关键字能排名在第二页第三位，应该会带来很多流量，其实本站点并非如此，大部分的流量来源都是从长尾关键字而来的，同时其转化率也还不错，下面是昨天本站的流量数据统计如图：

上图的流量数据98%的流量都是从长尾关键字而来的，再如图下所示：

上图所例举的数据就是该网站的流量来源，谈到这里可能就会有的新手站长会问，长尾关键字研究好了，那么怎么来利用长尾关键字获取流量呢?这是笔者重点要分享的。

当网站的相关长尾关键字研究好后，那么就以这些长尾关键字来做为内页的优化，也就是网站的内容建设，在对于内页进行优化时，以长尾关键字为主题，围绕该主题做好原创内容的建设，再在内容中做好合理的关键字布局，使整篇文章达到图文并茂的效果。如果该页面获得一定的权重后，那么当用户通过检索与该主题的关键字相匹配时，此时该页面就能有一个较好的排序，就能从该页面获得流量。如：笔者在所优化的咖啡网站中以长尾关键字“咖啡豆多少钱一斤”为主题撰写了一篇原创文章，现在每天都能通过该关键字获得流量3到5个IP 如下图该页面为着陆页：

⬬ 抓住关键字眼作文 ⬬

最近总是能被一些刚刚做站长的朋友问得无言以对，“搜索引擎怎么优化?”“怎么能让我的网站排名迅速靠前?”等等，其实我特喜欢和朋友们...

最近总是能被一些刚刚做站长的朋友问得无言以对，“搜索引擎怎么优化?”“怎么能让我的网站排名迅速靠前?”等等。其实我特喜欢和朋友们交流关于建站的一些问题，也很乐意把自己的一些经验分享给大家，可每次遇到这种问题我都无言以对，不是我不知道，是我根本就不知道从何说起。解释多了吧，问这种问题的朋友也不见得能真正的明白多少，敷衍吧，这还真不是我的作风。不得不承认，我也只不过是一个“茶壶”，煮饺子，这个真不行网络推广。

写这篇文章之前，百度搜了一下关于影响网站排名因素的文章，已经有很多朋友谈过此类的问题。虽然“雪中送炭”的人早已不是我，但我还是希望能“锦上添花”。当然了，对于建站之初的一些基础问题在这里就不谈了。不多扯，既然大家问到了，就和大家分享下我在“作战”的过程中总结的一些关于提高网站排名的小技巧。

更新，是每一个站长都很上心的问题。一个网站想生存，想发展，更新是必要条件。网站的更新，不单单可以让内容更加丰富多彩，也有利于蜘蛛更多的关注你的网站，对提高网站在同行业站点中的权威性很有作用，提高排名，自然也不在话下。而对于更新频率，我会从两个方面考虑。经过我在之前负责的几个站点更新时的总结发现，对于搜索引擎来讲，每周一更和每日一更的影响并不是特别的大，当然，这是在网站有一定得基础的前提下。而更新真正影响的是用户体验，一个网站更新频率越高，越有利于开发新用户，维护老用户。我想，这是我们所有站长的心愿。

所有SEO都知道，一个网站的内容好坏对排名的影响是十分巨大的，而原创纯度就是决定内容好坏的“金标准”。搜索引擎只不过是一个程序，大家没必要诚惶诚恐，虽然在检索文章重复率上有较高的识别能力，但在数以百亿计的文章面前，它不可能每一篇每一个字都进行分析，

前面我发表过关于如何提高文章的原创度的文章，这里不想多说，只送大家四个字“龙头凤尾”，这样做出来的伪原创，搞定蜘蛛不在话下网站推广。

高质量，高数量的外链对提高网站排名是很有帮助的，这个问题是现在很多站长都在谈论的。友情链接在这里我就不多说了，我相信只要接触到建站这块的朋友都清楚友情链接的作用。那么如何才能有效的提高网站外链的质量和数量呢?下面我主要从三点谈谈自己的一些经验。

1、关键词外链的交换;这个应该不难理解，举个例子;我现在做的是一个叫海淞医院的网站，在这个网站中的某篇文章中可能有个关键词的链接是指向上海天狮医院的，而前提是我和天狮网站的负责人谈好，在他们的文章中也会有相关的关键词链接指向我的网站。当然了，外链的相关度决定外链的质量，选择相关度高的网站交换链接也是很重要的。

2、软文;这个在我之前发表的文章中也提到过，相信很多成熟的站长都清楚软文的作用。也曾看到过有人反对软文用于推广，不过大家不得不承认，增加高质量的反向链接，会大大的促使网站收录的页数，而高收录又是每个站长都梦寐以求的。

网络推广，想提高网站的排名，宣传也是必不可少的。这时我们就需要一些高质量的博客和论坛了。A5、站长站、百度中心、新浪、搜狐、网易等等权重如此之高的博客和论坛已经给我们提供了一个如此接近百度的平台，那我们还在等什么呢?放心大胆的宣传吧，在这里，你可以毫无顾忌的发表任何方式的宣传文章。当然了，我们都是高素质的人，灌水滴不要。

提升网站排名并不难，方法也有很多，但如“安瑞克”般快速起效的却基本没有。只能从细节入手，站在搜索引擎优化的角度，全面的把握网站的综合因素，才能让每一个站长的努力都能够得到相应的回报。

惯例，感谢各位朋友对歪歪小兄的信任和支持。同时，也希望各位能在闲暇之余稍微动用下你那尊贵的手指，到小弟的网站扫扫，刚刚接手不久，希望大家能多多指点，共同进步。

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