blocks|key|309809|text|关于documentation，对于varchar(n)类型定义没有明确的限制。但是：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|309810|309811|+...|blockquote|309812|309813|在任何情况下，可以存储的最长字符串大约是1+GB。(数据类型声明中允许的n的最大值小于该值。更改这一点并不是很有用，因为使用多字节字符编码时，字符和字节的数量可能会有很大的不同。如果您希望存储没有特定上限的长字符串，请使用不带长度说明符的文本或字符，而不是编造任意的长度限制。)|309814|309815|还要注意这一点：|309816|309817|+提示：这三种类型之间没有性能差异，除了在使用空白填充类型时增加了存储空间，以及在存储到长度受限的列时需要几个额外的CPU周期来检查长度。虽然character(n)在其他一些数据库系统中具有性能优势，但在PostgreSQL中没有这种优势；事实上，character(n)通常是三者中最慢的，因为它需要额外的存储成本。在大多数情况下，应该使用文本或字符变化。|BOLD|309818|309819|entityMap|0|LINK|mutability|MUTABLE|url|http://www.postgresql.org/docs/current/static/datatype-character.html^0|I|A|2|D|0|0|0|0|0|10|1|0|0|0|0|1|3|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@$9|13|A|14|B|C]]|D|@$9|15|A|16|1|17]]|E|$]]|$1|F|3|-4|5|6|7|18|8|@]|D|@]|E|$]]|$1|G|3|H|5|I|7|19|8|@]|D|@]|E|$]]|$1|J|3|-4|5|6|7|1A|8|@]|D|@]|E|$]]|$1|K|3|L|5|6|7|1B|8|@$9|1C|A|1D|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|1E|8|@]|D|@]|E|$]]|$1|N|3|O|5|6|7|1F|8|@]|D|@]|E|$]]|$1|P|3|-4|5|6|7|1G|8|@]|D|@]|E|$]]|$1|Q|3|R|5|I|7|1H|8|@$9|1I|A|1J|B|S]]|D|@]|E|$]]|$1|T|3|-4|5|6|7|1K|8|@]|D|@]|E|$]]|$1|U|3|-4|5|6|7|1L|8|@]|D|@]|E|$]]]|V|$W|$5|X|Y|Z|E|$10|11]]]]

Referring to the <a href="http://www.postgresql.org/docs/current/static/datatype-character.html" rel="noreferrer">documentation</a>, there is no explicit limit given for the <code>varchar(n)</code> type definition. But:

<blockquote>
 ... 
 In any case, the longest possible
 character string that can be stored is
 about 1 GB. (The maximum value that
 will be allowed for <code>n</code> in the data type
 declaration is less than that. It
 wouldn't be very useful to change this
 because with multibyte character
 encodings the number of characters and
 bytes can be quite different anyway.
 If you desire to store long strings
 with no specific upper limit, use text
 or character varying without a length
 specifier, rather than making up an
 arbitrary length limit.)
</blockquote>

Also note this:

<blockquote>
 Tip: There is no performance
 difference among these three types,
 apart from increased storage space
 when using the blank-padded type, and
 a few extra CPU cycles to check the
 length when storing into a
 length-constrained column. While
 character(n) has performance
 advantages in some other database
 systems, there is no such advantage in
 PostgreSQL; in fact character(n) is
 usually the slowest of the three
 because of its additional storage
 costs. In most situations text or
 character varying should be used
 instead.
</blockquote>

blocks|key|307707|text|来自documentation|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|307708|307709|在任何情况下，可以存储的最长字符串大约为1+GB。|blockquote|307710|307711|entityMap|0|LINK|mutability|MUTABLE|url|http://www.postgresql.org/docs/current/static/datatype-character.html^0|2|D|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|-4|5|6|7|U|8|@]|9|@]|C|$]]|$1|E|3|F|5|G|7|V|8|@]|9|@]|C|$]]|$1|H|3|-4|5|6|7|W|8|@]|9|@]|C|$]]|$1|I|3|-4|5|6|7|X|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

From <a href="http://www.postgresql.org/docs/current/static/datatype-character.html" rel="nofollow noreferrer">documentation</a>:

<blockquote>
 In any case, the longest possible character string that can be stored is about 1 GB.
</blockquote>

blocks|key|304730|text|postgresql中的字符类型|type|unstyled|depth|inlineStyleRanges|entityRanges|data|304731|可变字符变化(N)，limit|304732|character(n)，字符长度可变(N)，字符长度可变(N)=固定长度，空白填充的|unordered-list-item|304733|304734|=可变无限长度|304735|304736|基于您的问题，我建议您使用text类型。该类型不需要字符长度。|offset|length|style|BOLD|304737|304738|此外，PostgreSQL还提供了text类型，它可以存储任意长度的字符串。尽管text类型不在SQL标准中，但其他几个SQL数据库管理系统也有它。|blockquote|304739|304740|304741|来源：https://www.postgresql.org/docs/9.6/static/datatype-character.html|304742|entityMap|0|LINK|mutability|MUTABLE|url|https://www.postgresql.org/docs/9.6/static/datatype-character.html^0|0|0|0|0|0|0|D|4|0|0|H|4|0|0|0|3|1U|0|0^^$0|@$1|2|3|4|5|6|7|16|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|17|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|18|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|19|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|1A|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|1B|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|1C|8|@$M|1D|N|1E|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|1F|8|@]|9|@]|A|$]]|$1|R|3|S|5|T|7|1G|8|@$M|1H|N|1I|O|P]]|9|@]|A|$]]|$1|U|3|-4|5|6|7|1J|8|@]|9|@]|A|$]]|$1|V|3|-4|5|6|7|1K|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|1L|8|@]|9|@$M|1M|N|1N|1|1O]]|A|$]]|$1|Y|3|-4|5|6|7|1P|8|@]|9|@]|A|$]]]|Z|$10|$5|11|12|13|A|$14|15]]]]

character type in postgresql 

<ul>
<li>character varying(n), varchar(n) = variable-length with limit</li>
<li>character(n), char(n) = fixed-length, blank padded</li>
<li>text = variable unlimited length</li>
</ul>

based on your problem I suggest you to use type text. the type does not require character length.

<blockquote>
 In addition, PostgreSQL provides the text type, which stores strings of any length. Although the type text is not in the SQL standard, several other SQL database management systems have it as well.
</blockquote>

source : <a href="https://www.postgresql.org/docs/9.6/static/datatype-character.html" rel="nofollow noreferrer">https://www.postgresql.org/docs/9.6/static/datatype-character.html</a>

blocks|key|307734|text|最大字符串大小约为1+GB。根据postgres+docs|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|307735|307736|超长值也存储在后台表中，因此它们不会干扰对较短列值的快速访问。在任何情况下，可以存储的最长字符串大约是1+GB。(数据类型声明中允许的n的最大值小于该值。)|blockquote|307737|307738|307739|请注意，您可以为varchar指定的最大n小于最大存储大小。虽然这一限制可能会有所不同，但快速检查后会发现postgres11.2上的限制是10MB|307740|psql+(11.2)

=>+create+table+varchar_test+(name+varchar(1073741824));
ERROR:++length+for+type+varchar+cannot+exceed+10485760|code-block|syntax|javascript|307741|实际上，当您没有合理的长度限制时，只使用varchar而不指定长度限制就是suggested。根据官方文件，|CODE|307742|307743|如果您希望存储没有特定上限的长字符串，请使用不带长度说明符的文本或字符，而不是构成任意长度限制。|307744|307745|entityMap|0|LINK|mutability|MUTABLE|url|https://www.postgresql.org/docs/current/datatype-character.html|1|https://wiki.postgresql.org/wiki/Don%2527t_Do_This#Don.27t_use_varchar.28n.29_by_default^0|9|4|P|4|0|0|0|1V|1|0|0|0|K|1|1Y|4|0|0|K|7|11|9|1|0|0|0|0^^$0|@$1|2|3|4|5|6|7|19|8|@$9|1A|A|1B|B|C]]|D|@$9|1C|A|1D|1|1E]]|E|$]]|$1|F|3|-4|5|6|7|1F|8|@]|D|@]|E|$]]|$1|G|3|H|5|I|7|1G|8|@$9|1H|A|1I|B|C]]|D|@]|E|$]]|$1|J|3|-4|5|6|7|1J|8|@]|D|@]|E|$]]|$1|K|3|-4|5|6|7|1K|8|@]|D|@]|E|$]]|$1|L|3|M|5|6|7|1L|8|@$9|1M|A|1N|B|C]|$9|1O|A|1P|B|C]]|D|@]|E|$]]|$1|N|3|O|5|P|7|1Q|8|@]|D|@]|E|$Q|R]]|$1|S|3|T|5|6|7|1R|8|@$9|1S|A|1T|B|U]]|D|@$9|1U|A|1V|1|1W]]|E|$]]|$1|V|3|-4|5|6|7|1X|8|@]|D|@]|E|$]]|$1|W|3|X|5|I|7|1Y|8|@]|D|@]|E|$]]|$1|Y|3|-4|5|6|7|1Z|8|@]|D|@]|E|$]]|$1|Z|3|-4|5|6|7|20|8|@]|D|@]|E|$]]]|10|$11|$5|12|13|14|E|$15|16]]|17|$5|12|13|14|E|$15|18]]]]

The maximum string size is about 1 GB. Per the postgres <a href="https://www.postgresql.org/docs/current/datatype-character.html" rel="nofollow noreferrer">docs</a>:

<blockquote>
 Very long values are also stored in background tables so that they do not interfere with rapid access to shorter column values. In any case, the longest possible character string that can be stored is about 1 GB. (The maximum value that will be allowed for n in the data type declaration is less than that.)
</blockquote>

Note that the max n you can specify for varchar is less than the max storage size. While this limit may vary, a quick check reveals that the limit on postgres 11.2 is 10 MB:

<pre><code>psql (11.2)

=&gt; create table varchar_test (name varchar(1073741824));
ERROR: length for type varchar cannot exceed 10485760
</code></pre>

Practically speaking, when you do not have a well rationalized length limit, it's <a href="https://wiki.postgresql.org/wiki/Don%27t_Do_This#Don.27t_use_varchar.28n.29_by_default" rel="nofollow noreferrer">suggested</a> that you simply use <code>varchar</code> without specifying one. Per the official docs,

<blockquote>
 If you desire to store long strings with no specific upper limit, use text or character varying without a length specifier, rather than making up an arbitrary length limit.
</blockquote>

I am using character varying data type in PostgreSQL. 
I was not able to find this information in PostgreSQL manual.
What is max limit of characters in character varying data type?

PostgreSQL character varying length limit

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我在PostgreSQL中使用字符变化数据类型。我在PostgreSQL手册中找不到这些信息。字符变化数据类型的最大字符数限制是多少？

问PostgreSQL字符可变长度限制
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