如下所示：
| 名字 | 描述 |
|---|---|
| character varying(n), varchar(n) | 变长，有长度限制 |
| character(n), char(n) | 定长，不足补空白 |
| text | 变长，无长度限制 |
简单来说，varchar的长度可变，而char的长度不可变，对于postgresql数据库来说varchar和char的区别仅仅在于前者是变长，而后者是定长，最大长度都是10485760（1GB）
varchar不指定长度，可以存储最大长度（1GB）的字符串，而char不指定长度，默认则为1，这点需要注意。
text类型：在postgresql数据库里边，text和varchar几乎无性能差别，区别仅在于存储结构的不同
对于char的使用，应该在确定字符串长度的情况下使用，否则应该选择varchar或者text
SQL定义了两种基本的字符类型：character varying(n) 和character(n)，这里的n 是一个正整数。两种类型都可以存储最多n个字符的字符串（没有字节）。试图存储更长的字符串到这些类型的字段里会产生一个错误，除非超出长度的字符都是空白，这种情况下该字符串将被截断为最大长度。这个看上去有点怪异的例外是SQL标准要求的。如果要存储的字符串比声明的长度短，类型为character的数值将会用空白填满；而类型为character varying的数值将只是存储短些的字符串。
如果我们明确地把一个数值转换成character varying(n) 或character(n)，那么超长的数值将被截断成n 个字符，且不会抛出错误。这也是SQL标准的要求。
varchar(n)和char(n) 分别是character varying(n) 和character(n)的别名，没有声明长度的character等于character(1)；如果不带长度说明词使用character varying，那么该类型接受任何长度的字符串。后者是PostgreSQL的扩展。
另外，PostgreSQL提供text类型，它可以存储任何长度的字符串。尽管类型text不是SQL 标准，但是许多其它SQL数据库系统也有它。
character类型的数值物理上都用空白填充到指定的长度n，并且以这种方式存储和显示。不过，填充的空白是无语意的。在比较两个character 值的时候，填充的空白都不会被关注，在转换成其它字符串类型的时候， character值里面的空白会被删除。请注意，在character varying和text数值里，结尾的空白是有语意的。并且当使用模式匹配时，如LIKE，使用正则表达式。
一个简短的字符串（最多126个字节）的存储要求是1个字节加上实际的字符串，其中包括空格填充的character。更长的字符串有4个字节的开销，而不是1。长的字符串将会自动被系统压缩，因此在磁盘上的物理需求可能会更少些。更长的数值也会存储在后台表里面，这样它们就不会干扰对短字段值的快速访问。不管怎样，允许存储的最长字符串大概是1GB 。允许在数据类型声明中出现的n 的最大值比这还小。修改这个行为没有什么意义，因为在多字节编码下字符和字节的数目可能差别很大。如果你想存储没有特定上限的长字符串，那么使用text 或没有长度声明的character varying，而不要选择一个任意长度限制。
提示： 这三种类型之间没有性能差别，除了当使用填充空白类型时的增加存储空间，和当存储长度约束的列时一些检查存入时长度的额外的CPU周期。虽然在某些其它的数据库系统里，character(n) 有一定的性能优势，但在PostgreSQL里没有。事实上，character(n)通常是这三个中最慢的，因为额外存储成本。在大多数情况下，应该使用text 或character varying。
补充：使用PostGreSQL数据库进行text录入和text检索
中文分词
ChineseParse.cs
using System;
using System.Collections;
using System.IO;
using System.Text.RegularExpressions;
namespace FullTextSearch.Common
{
///
/// 中文分词器。
///
public class ChineseParse
{
private static readonly ChineseWordsHashCountSet _countTable;
static ChineseParse()
{
_countTable = new ChineseWordsHashCountSet();
InitFromFile("ChineseDictionary.txt");
}
///
/// 从指定的文件中初始化中文词语字典和字符串次数字典。
///
/// 文件名
private static void InitFromFile(string fileName)
{
string path = Path.Combine(Directory.GetCurrentDirectory(), @"..\..\Common\", fileName);
if (File.Exists(path))
{
using (StreamReader sr = File.OpenText(path))
{
string s = "";
while ((s = sr.ReadLine()) != null)
{
ChineseWordUnit _tempUnit = InitUnit(s);
_countTable.InsertWord(_tempUnit.Word);
}
}
}
}
///
/// 将一个字符串解析为ChineseWordUnit。
///
/// 字符串
/// 解析得到的ChineseWordUnit
/// 4
/// 0
private static ChineseWordUnit InitUnit(string s)
{
var reg = new Regex(@"\s+");
string[] temp = reg.Split(s);
//if (temp.Length != 2)
//{
// throw new Exception("字符串解析错误：" + s);
//}
if (temp.Length != 1)
{
throw new Exception("字符串解析错误：" + s);
}
return new ChineseWordUnit(temp[0], Int32.Parse("1"));
}
///
/// 分析输入的字符串，将其切割成一个个的词语。
///
/// 待切割的字符串
/// 所切割得到的中文词语数组
public static string[] ParseChinese(string s)
{
int _length = s.Length;
string _temp = String.Empty;
var _words = new ArrayList();
for (int i = 0; i 1)
{
int j = 2;
for (; i + j 0; j++)
{
}
_temp = s.Substring(i, j - 1);
i = i + j - 2;
}
i++;
_words.Add(_temp);
}
var _tempStringArray = new string[_words.Count];
_words.CopyTo(_tempStringArray);
return _tempStringArray;
}
}
}
ChineseWordsHashCountSet.cs
using System.Collections;
namespace FullTextSearch.Common
{
///
/// 记录字符串出现在中文字典所录中文词语的前端的次数的字典类。如字符串"中"出现在"中国"的前端，则在字典中记录一个次数。
///
public class ChineseWordsHashCountSet
{
///
/// 记录字符串在中文词语中出现次数的Hashtable。键为特定的字符串，值为该字符串在中文词语中出现的次数。
///
private readonly Hashtable _rootTable;
///
/// 类型初始化。
///
public ChineseWordsHashCountSet()
{
_rootTable = new Hashtable();
}
///
/// 查询指定字符串出现在中文字典所录中文词语的前端的次数。
///
/// 指定字符串
/// 字符串出现在中文字典所录中文词语的前端的次数。若为-1，表示不出现。
public int GetCount(string s)
{
if (!_rootTable.ContainsKey(s.Length))
{
return -1;
}
var _tempTable = (Hashtable) _rootTable[s.Length];
if (!_tempTable.ContainsKey(s))
{
return -1;
}
return (int) _tempTable[s];
}
///
/// 向次数字典中插入一个词语。解析该词语，插入次数字典。
///
/// 所处理的字符串。
public void InsertWord(string s)
{
for (int i = 0; i
/// 向次数字典中插入一个字符串的次数记录。
///
/// 所插入的字符串。
private void InsertSubString(string s)
{
if (!_rootTable.ContainsKey(s.Length) && s.Length > 0)
{
var _newHashtable = new Hashtable();
_rootTable.Add(s.Length, _newHashtable);
}
var _tempTable = (Hashtable) _rootTable[s.Length];
if (!_tempTable.ContainsKey(s))
{
_tempTable.Add(s, 1);
}
else
{
_tempTable[s] = (int) _tempTable[s] + 1;
}
}
}
}
ChineseWordUnit.cs
namespace FullTextSearch.Common
{
public struct ChineseWordUnit
{
private readonly int _power;
private readonly string _word;
///
/// 结构初始化。
///
/// 中文词语
/// 该词语的权重
public ChineseWordUnit(string word, int power)
{
_word = word;
_power = power;
}
///
/// 中文词语单元所对应的中文词。
///
public string Word
{
get { return _word; }
}
///
/// 该中文词语的权重。
///
public int Power
{
get { return _power; }
}
}
}
ChineseDictionary.txt
主窗体界面
MainManager.cs
using System;
using System.Collections.Generic;
using System.Data;
using System.Drawing;
using System.Windows.Forms;
using FullTextSearch.Common;
using Npgsql;
namespace FullTextSearch
{
public partial class MainManager : Form
{
private readonly PostgreSQL pg = new PostgreSQL();
private readonly SQLquerys sqlQuerys = new SQLquerys();
private char analysisType;
private string createCOnnString= "";
private DataSet dataSet = new DataSet();
private DataTable dataTable = new DataTable();
private char odabirAndOr;
private char vrstaPretrazivanja;
public MainManager()
{
InitializeComponent();
rbtn_AND.Checked = true;
rbtnNeizmjenjeni.Checked = true;
odabirAndOr = '*';
radioButton_Day.Checked = true;
radioButton_Day.Checked = true;
}
private void Form1_Load(object sender, EventArgs e)
{
gb_unosPodataka.Enabled = false;
groupBox_Search.Enabled = false;
groupBox_Analysis.Enabled = false;
button_Disconnect.Enabled = false;
button_Pretrazi.BackColor = Color.WhiteSmoke;
button_Disconnect.BackColor = Color.WhiteSmoke;
button_unosTekstaUBazu.BackColor = Color.WhiteSmoke;
button1.BackColor = Color.WhiteSmoke;
}
private void button_unosTekstaUBazu_Click(object sender, EventArgs e)
{
string searchTextBoxString = rTB_unosTextaUBazu.Text;
if (searchTextBoxString != "")
{
pg.insertIntoTable(searchTextBoxString, pg.conn);
MessageBox.Show(searchTextBoxString + " 添加到数据库!");
rTB_unosTextaUBazu.Clear();
}
else
{
MessageBox.Show("不允许空数据!");
}
}
private void button_Pretrazi_Click(object sender, EventArgs e)
{
string stringToSearch;
string sql;
string highlitedText;
string rank;
string check;
stringToSearch = txt_Search.Text.Trim();
var list = new List(ChineseParse.ParseChinese(stringToSearch));
;
sql = sqlQuerys.createSqlString(list, odabirAndOr, vrstaPretrazivanja);
richTextBox1.Text = sql;
check = sqlQuerys.testIfEmpty(stringToSearch);
pg.insertIntoAnalysisTable(stringToSearch, pg.conn);
pg.openConnection();
var command = new NpgsqlCommand(sql, pg.conn);
NpgsqlDataReader reader = command.ExecuteReader();
int count = 0;
linkLabel_Rezultat.Text = " ";
while (reader.Read())
{
highlitedText = reader[1].ToString();
rank = reader[3].ToString();
linkLabel_Rezultat.Text += highlitedText + "[" + rank + "]\n";
count++;
}
labelBrojac.Text = "找到的文件数量: " + count;
pg.closeConnection();
}
private void rbtn_AND_CheckedChanged(object sender, EventArgs e)
{
odabirAndOr = '*';
}
private void rbtn_OR_CheckedChanged(object sender, EventArgs e)
{
odabirAndOr = '+';
}
private void rbtnNeizmjenjeni_CheckedChanged(object sender, EventArgs e)
{
vrstaPretrazivanja = 'A';
}
private void rbtn_Rijecnici_CheckedChanged(object sender, EventArgs e)
{
vrstaPretrazivanja = 'B';
}
private void rbtn_Fuzzy_CheckedChanged(object sender, EventArgs e)
{
vrstaPretrazivanja = 'C';
}
private void button_Connect_Click(object sender, EventArgs e)
{
if (connectMe())
{
gb_unosPodataka.Enabled = true;
groupBox_Search.Enabled = true;
groupBox_Analysis.Enabled = true;
textBox_Database.Enabled = false;
textBox_IP.Enabled = false;
textBox_Port.Enabled = false;
textBox_Password.Enabled = false;
textBox_UserID.Enabled = false;
button_Connect.Enabled = false;
button_Disconnect.Enabled = true;
button_Pretrazi.BackColor = Color.SkyBlue;
button_Disconnect.BackColor = Color.IndianRed;
button_unosTekstaUBazu.BackColor = Color.MediumSeaGreen;
button1.BackColor = Color.MediumSeaGreen;
button_Connect.BackColor = Color.WhiteSmoke;
}
}
private void button_Disconnect_Click(object sender, EventArgs e)
{
gb_unosPodataka.Enabled = false;
groupBox_Search.Enabled = false;
groupBox_Analysis.Enabled = false;
textBox_Database.Enabled = true;
textBox_IP.Enabled = true;
textBox_Port.Enabled = true;
textBox_Password.Enabled = true;
textBox_UserID.Enabled = true;
button_Connect.Enabled = true;
button_Disconnect.Enabled = false;
button_Pretrazi.BackColor = Color.WhiteSmoke;
button_Disconnect.BackColor = Color.WhiteSmoke;
button_unosTekstaUBazu.BackColor = Color.WhiteSmoke;
button1.BackColor = Color.WhiteSmoke;
button_Connect.BackColor = Color.MediumSeaGreen;
txt_Search.Text = "";
linkLabel_Rezultat.Text = "";
richTextBox1.Text = "";
labelBrojac.Text = "";
}
private bool connectMe()
{
createConnString += "Server=" + textBox_IP.Text + ";Port=" + textBox_Port.Text + ";User Id=" +
textBox_UserID.Text + ";Password=" + textBox_Password.Text + ";Database=" +
textBox_Database.Text + ";";
sqlQuerys.setTheKey(createConnString);
pg.setConnectionString();
pg.setConnection();
if (pg.openConnection())
{
MessageBox.Show("您已成功连接!");
pg.closeConnection();
return true;
}
return false;
}
private void button1_Click(object sender, EventArgs e)
{
string selectedTimestamp;
selectedTimestamp = dateTimePicker_From.Value.ToString("dd-MM-yyyy hh:mm:ss") + " " +
dateTimePicker_To.Value.ToString("dd-MM-yyyy hh:mm:ss");
var analize = new Analysis(selectedTimestamp, analysisType);
analize.Show();
}
private void radioButton_Day_CheckedChanged(object sender, EventArgs e)
{
analysisType = 'D';
}
private void radioButton_Hour_CheckedChanged(object sender, EventArgs e)
{
analysisType = 'H';
}
}
}
SQLquerys.cs代码:
using System.Collections.Generic;
namespace FullTextSearch
{
internal class SQLquerys
{
private static string giveMeTheKey;
private static int tempInt = 1;
//设置连接字符串
public void setTheKey(string connString)
{
giveMeTheKey = connString;
giveMeTheKey += "";
}
//将连接字符串存储在静态变量中
public string getTheKey()
{
giveMeTheKey += "";
return giveMeTheKey;
}
public void setCounter()
{
tempInt = 1;
}
//根据AND和OR的选择分析字符串进行搜索
public string createFunctionString(List searchList, char selector)
{
string TempString = "";
string[] TempField = null;
int i = 0;
int j = 0;
foreach (string searchStringInList in searchList)
{
if (j != 0)
{
if (selector == '+')
TempString = TempString + " | ";
else if (selector == '*')
TempString = TempString + " & ";
}
j = 1;
TempField = splitListForInput(searchStringInList);
TempString = TempString + "(";
foreach (string justTempString in TempField)
{
if (i != 0)
{
TempString = TempString + " & ";
}
TempString = TempString + justTempString;
i = 1;
}
TempString = TempString + ")";
i = 0;
}
return TempString;
}
//帮助方法
public List splitInputField(string[] inputField)
{
var unfinishedList = new List();
foreach (string splitString in inputField)
{
unfinishedList.Add(splitString);
}
return unfinishedList;
}
//帮助方法
public string[] splitListForInput(string inputString)
{
string[] parsedList = null;
parsedList = inputString.Split(' ');
return parsedList;
}
//在PostgreSQL中创建ts功能的功能，用于字典搜索
public string createTsFunction(string tsString)
{
string tsHeadline = "";
string tsRank = "";
string tsFunction = "";
tsHeadline = ",\n ts_headline(\"content\", to_tsquery('" + tsString + "')), \"content\"";
tsRank = ",\n ts_rank(to_tsvector(\"content\"), to_tsquery('" + tsString + "')) rank";
tsFunction = tsHeadline + tsRank;
return tsFunction;
}
//创建SQL查询依赖于选择哪种类型的搜索，也取决于AND或OR选择器
public string createSqlString(List searchList, char selector, char vrstaPretrazivanja)
{
string selectString = "";
string myTempString = "";
string TempString = "";
int i = 0;
TempString = createFunctionString(searchList, selector);
TempString = createTsFunction(TempString);
selectString = "SELECT \"id\"" + TempString + "\nFROM \"texttable\" \nWHERE ";
if (vrstaPretrazivanja == 'A')
{
foreach (string myString in searchList)
{
if (i == 0)
{
myTempString = myTempString + "\"content\" LIKE '%" + myString + "%' ";
i++;
}
else
{
if (selector == '*')
myTempString = myTempString + "\nAND \"content\" LIKE '%" + myString + "%' ";
else if (selector == '+')
myTempString = myTempString + "\nOR \"content\" LIKE '%" + myString + "%' ";
}
}
}
else if (vrstaPretrazivanja == 'B')
{
foreach (string myString in searchList)
{
string temporalString = "";
string[] testingString = myString.Split(' ');
for (int k = 0; k
PostgreSQL.cs代码:
using System;
using System.Windows.Forms;
using Npgsql;
using NpgsqlTypes;
namespace FullTextSearch
{
public class PostgreSQL
{
private static int tempInt = 1;
private readonly SQLquerys sql = new SQLquerys();
public NpgsqlConnection conn;
public string connectionstring;
private string newConnString;
public PostgreSQL()
{
setConnectionString();
setConnection();
}
public void setConnectionString()
{
newCOnnString= sql.getTheKey();
cOnnectionstring= String.Format(newConnString);
setConnection();
}
public void setConnection()
{
cOnn= new NpgsqlConnection(connectionstring);
}
public bool openConnection()
{
try
{
conn.Open();
return true;
}
catch
{
MessageBox.Show("Unable to connect! Check parameters!");
return false;
}
}
public void closeConnection()
{
conn.Close();
}
public void insertIntoTable(string textToInsert, NpgsqlConnection nsqlConn)
{
string mySqlString = "INSERT INTO \"texttable\" (\"content\") VALUES (@Param1)";
var myParameter = new NpgsqlParameter("@Param1", NpgsqlDbType.Text);
myParameter.Value = textToInsert;
openConnection();
var myCommand = new NpgsqlCommand(mySqlString, nsqlConn);
myCommand.Parameters.Add(myParameter);
myCommand.ExecuteNonQuery();
closeConnection();
}
public void insertIntoAnalysisTable(string textToInsert, NpgsqlConnection nsqlConn)
{
string dateTime = DateTime.Now.ToString();
string[] temp;
temp = dateTime.Split(' ');
string mySqlString =
"INSERT INTO \"analysistable\" (\"searchedtext\", \"dateofsearch\", \"timeofsearch\") VALUES ('" +
textToInsert + "', '" + temp[0] + "'" + ", '" + temp[1] + "');";
openConnection();
var myCommand = new NpgsqlCommand(mySqlString, nsqlConn);
myCommand.ExecuteNonQuery();
closeConnection();
}
public void executeQuery(string queryText, NpgsqlConnection nsqlConn)
{
openConnection();
var myCommand = new NpgsqlCommand(queryText, nsqlConn);
myCommand.ExecuteNonQuery();
closeConnection();
}
public void createTempTable(NpgsqlConnection nsqlConn, char analysisType, string dateFrom, string dateTo,
string splitMe)
{
if (analysisType == 'H')
{
string dropIfExists = "DROP TABLE IF EXISTS \"sat\";";
string createTempTable = "CREATE TABLE IF NOT EXISTS \"sat\" (rbrSata INT);";
string insertIntoTempTable = "";
for (int i = 0; i <24; i++)
{
insertIntoTempTable += "INSERT INTO \"sat\" VALUES (" + i + ");";
}
openConnection();
var commandDrop = new NpgsqlCommand(dropIfExists, nsqlConn);
commandDrop.ExecuteNonQuery();
var commandCreate = new NpgsqlCommand(createTempTable, nsqlConn);
commandCreate.ExecuteNonQuery();
var commandInsert = new NpgsqlCommand(insertIntoTempTable, nsqlConn);
commandInsert.ExecuteNonQuery();
closeConnection();
}
else if (analysisType == 'D')
{
string dropIfExists = "DROP TABLE IF EXISTS \"dan\";";
string createTempTable = "CREATE TABLE IF NOT EXISTS \"dan\" (rbrDana INT);";
string insertIntoTempTable = splitMe;
openConnection();
var commandDrop = new NpgsqlCommand(dropIfExists, nsqlConn);
commandDrop.ExecuteNonQuery();
var commandCreate = new NpgsqlCommand(createTempTable, nsqlConn);
commandCreate.ExecuteNonQuery();
var commandInsert = new NpgsqlCommand(insertIntoTempTable, nsqlConn);
commandInsert.ExecuteNonQuery();
closeConnection();
}
}
}
}
PostGreSQL sql脚本:
CREATE TABLE public.analysistable
(
id integer NOT NULL DEFAULT nextval('analysistable_id_seq'::regclass),
searchedtext text COLLATE pg_catalog."default" NOT NULL,
dateofsearch date NOT NULL,
timeofsearch time without time zone NOT NULL,
CONSTRAINT analysistable_pkey PRIMARY KEY (id)
)
WITH (
OIDS = FALSE
)
TABLESPACE pg_default;
ALTER TABLE public.analysistable
OWNER to king;
CREATE TABLE public.texttable
(
id integer NOT NULL DEFAULT nextval('texttable_id_seq'::regclass),
content text COLLATE pg_catalog."default" NOT NULL,
CONSTRAINT texttable_pkey PRIMARY KEY (id)
)
WITH (
OIDS = FALSE
)
TABLESPACE pg_default;
ALTER TABLE public.texttable
OWNER to king;
运行结果如图:
以上为个人经验，希望能给大家一个参考，也希望大家多多支持。如有错误或未考虑完全的地方，望不吝赐教。
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