我正在通过Java从SQL数据库中检索列名。我知道我也可以从ResultSet检索列名。所以我有这个SQL查询
select column_name from information_schema.columns where table_name='suppliers'
问题是我不知道如何从ResultSet获取列名，而我的代码是
public void getAllColumnNames() throws Exception{
String sql = "SELECT column_name from information_schema.columns where table_name='suppliers'";
PreparedStatement ps = connection.prepareStatement(sql);
ResultSet rs = ps.executeQuery(sql);
// extract values from rs
}
答案 0 :(得分：61)
ResultSet resultSet = statement.executeQuery("SELECT * from foo");
ResultSetMetaData rsmd = resultSet.getMetaData();
int columnsNumber = rsmd.getColumnCount();
while (resultSet.next()) {
for (int i = 1; i <= columnsNumber; i++) {
if (i > 1) System.out.print(", ");
String columnValue = resultSet.getString(i);
System.out.print(columnValue + " " + rsmd.getColumnName(i));
}
System.out.println("");
}
答案 1 :(得分：8)
1）而不是PreparedStatement使用Statement
2）在ResultSet执行查询后，在rs.getString()的帮助下提取值为：
Statement st=cn.createStatement();
ResultSet rs=st.executeQuery(sql);
while(rs.next())
{
rs.getString(1); //or rs.getString("column name");
}
答案 2 :(得分：3)
进一步使用
rs.getString(1);
rs.getInt(2);
1,2是表的列号，并按照coloumn的数据类型设置int或string
答案 3 :(得分：1)
查看documentation。你犯了以下错误。
首先，ps.executeQuery()没有任何参数。而是将SQL查询传递给它。
其次，关于准备好的语句，如果要传递任何参数，则必须使用?符号。然后使用
setXXX(index, value)
此处 xxx 代表数据类型。
答案 4 :(得分：1)
对于那些希望获得更好版本的结果集打印作为util类的用户 这对打印结果集确实很有帮助，并且可以通过util来完成许多工作……感谢Hami Torun！
在此类中，printResultSet以通用的方式使用ResultSetMetaData。
import java.sql.*;
import java.util.ArrayList;
import java.util.List;
import java.util.StringJoiner;
public final class DBTablePrinter {
/**
* Column type category for CHAR, VARCHAR
* and similar text columns.
*/
public static final int CATEGORY_STRING = 1;
/**
* Column type category for TINYINT, SMALLINT,
* INT and BIGINT columns.
*/
public static final int CATEGORY_INTEGER = 2;
/**
* Column type category for REAL, DOUBLE,
* and DECIMAL columns.
*/
public static final int CATEGORY_DOUBLE = 3;
/**
* Column type category for date and time related columns like
* DATE, TIME, TIMESTAMP etc.
*/
public static final int CATEGORY_DATETIME = 4;
/**
* Column type category for BOOLEAN columns.
*/
public static final int CATEGORY_BOOLEAN = 5;
/**
* Column type category for types for which the type name
* will be printed instead of the content, like BLOB,
* BINARY, ARRAY etc.
*/
public static final int CATEGORY_OTHER = 0;
/**
* Default maximum number of rows to query and print.
*/
private static final int DEFAULT_MAX_ROWS = 10;
/**
* Default maximum width for text columns
* (like a VARCHAR) column.
*/
private static final int DEFAULT_MAX_TEXT_COL_WIDTH = 150;
/**
* Overloaded method that prints rows from table tableName
* to standard out using the given database connection
* conn. Total number of rows will be limited to
* {@link #DEFAULT_MAX_ROWS} and
* {@link #DEFAULT_MAX_TEXT_COL_WIDTH} will be used to limit
* the width of text columns (like a VARCHAR column).
*
* @param conn Database connection object (java.sql.Connection)
* @param tableName Name of the database table
*/
public static void printTable(Connection conn, String tableName) {
printTable(conn, tableName, DEFAULT_MAX_ROWS, DEFAULT_MAX_TEXT_COL_WIDTH);
}
/**
* Overloaded method that prints rows from table tableName
* to standard out using the given database connection
* conn. Total number of rows will be limited to
* maxRows and
* {@link #DEFAULT_MAX_TEXT_COL_WIDTH} will be used to limit
* the width of text columns (like a VARCHAR column).
*
* @param conn Database connection object (java.sql.Connection)
* @param tableName Name of the database table
* @param maxRows Number of max. rows to query and print
*/
public static void printTable(Connection conn, String tableName, int maxRows) {
printTable(conn, tableName, maxRows, DEFAULT_MAX_TEXT_COL_WIDTH);
}
/**
* Overloaded method that prints rows from table tableName
* to standard out using the given database connection
* conn. Total number of rows will be limited to
* maxRows and
* maxStringColWidth will be used to limit
* the width of text columns (like a VARCHAR column).
*
* @param conn Database connection object (java.sql.Connection)
* @param tableName Name of the database table
* @param maxRows Number of max. rows to query and print
* @param maxStringColWidth Max. width of text columns
*/
public static void printTable(Connection conn, String tableName, int maxRows, int maxStringColWidth) {
if (conn == null) {
System.err.println("DBTablePrinter Error: No connection to database (Connection is null)!");
return;
}
if (tableName == null) {
System.err.println("DBTablePrinter Error: No table name (tableName is null)!");
return;
}
if (tableName.length() == 0) {
System.err.println("DBTablePrinter Error: Empty table name!");
return;
}
if (maxRows
* ResultSet to standard out using {@link #DEFAULT_MAX_TEXT_COL_WIDTH}
* to limit the width of text columns.
*
* @param rs The ResultSet to print
*/
public static void printResultSet(ResultSet rs) {
printResultSet(rs, DEFAULT_MAX_TEXT_COL_WIDTH);
}
/**
* Overloaded method to print rows of a
* ResultSet to standard out using maxStringColWidth
* to limit the width of text columns.
*
* @param rs The ResultSet to print
* @param maxStringColWidth Max. width of text columns
*/
public static void printResultSet(ResultSet rs, int maxStringColWidth) {
try {
if (rs == null) {
System.err.println("DBTablePrinter Error: Result set is null!");
return;
}
if (rs.isClosed()) {
System.err.println("DBTablePrinter Error: Result Set is closed!");
return;
}
if (maxStringColWidth columns = new ArrayList(columnCount);
// List of table names. Can be more than one if it is a joined
// table query
List tableNames = new ArrayList(columnCount);
// Get the columns and their meta data.
// NOTE: columnIndex for rsmd.getXXX methods STARTS AT 1 NOT 0
for (int i = 1; i maxStringColWidth) {
value = value.substring(0, maxStringColWidth - 3) + "...";
}
break;
}
// Adjust the column width
c.setWidth(value.length() > c.getWidth() ? value.length() : c.getWidth());
c.addValue(value);
} // END of for loop columnCount
rowCount++;
} // END of while (rs.next)
/*
At this point we have gone through meta data, get the
columns and created all Column objects, iterated over the
ResultSet rows, populated the column values and adjusted
the column widths.
We cannot start printing just yet because we have to prepare
a row separator String.
*/
// For the fun of it, I will use StringBuilder
StringBuilder strToPrint = new StringBuilder();
StringBuilder rowSeparator = new StringBuilder();
/*
Prepare column labels to print as well as the row separator.
It should look something like this:
+--------+------------+------------+-----------+ (row separator)
| EMP_NO | BIRTH_DATE | FIRST_NAME | LAST_NAME | (labels row)
+--------+------------+------------+-----------+ (row separator)
*/
// Iterate over columns
for (Column c : columns) {
int width = c.getWidth();
// Center the column label
String toPrint;
String name = c.getLabel();
int diff = width - name.length();
if ((diff % 2) == 1) {
// diff is not divisible by 2, add 1 to width (and diff)
// so that we can have equal padding to the left and right
// of the column label.
width++;
diff++;
c.setWidth(width);
}
int paddingSize = diff / 2; // InteliJ says casting to int is redundant.
// Cool String repeater code thanks to user102008 at stackoverflow.com
String padding = new String(new char[paddingSize]).replace("\0", " ");
toPrint = "| " + padding + name + padding + " ";
// END centering the column label
strToPrint.append(toPrint);
rowSeparator.append("+");
rowSeparator.append(new String(new char[width + 2]).replace("\0", "-"));
}
String lineSeparator = System.getProperty("line.separator");
// Is this really necessary ??
lineSeparator = lineSeparator == null ? "\n" : lineSeparator;
rowSeparator.append("+").append(lineSeparator);
strToPrint.append("|").append(lineSeparator);
strToPrint.insert(0, rowSeparator);
strToPrint.append(rowSeparator);
StringJoiner sj = new StringJoiner(", ");
for (String name : tableNames) {
sj.add(name);
}
String info = "Printing " + rowCount;
info += rowCount > 1 ? " rows from " : " row from ";
info += tableNames.size() > 1 ? "tables " : "table ";
info += sj.toString();
System.out.println(info);
// Print out the formatted column labels
System.out.print(strToPrint.toString());
String format;
// Print out the rows
for (int i = 0; i
* Integers should not be truncated so column widths should
* be adjusted without a column width limit. Text columns should be
* left justified and can be truncated to a max. column width etc...
*
* See also:
* java.sql.Types
*
* @param type Generic SQL type
* @return The category this type belongs to
*/
private static int whichCategory(int type) {
switch (type) {
case Types.BIGINT:
case Types.TINYINT:
case Types.SMALLINT:
case Types.INTEGER:
return CATEGORY_INTEGER;
case Types.REAL:
case Types.DOUBLE:
case Types.DECIMAL:
return CATEGORY_DOUBLE;
case Types.DATE:
case Types.TIME:
case Types.TIME_WITH_TIMEZONE:
case Types.TIMESTAMP:
case Types.TIMESTAMP_WITH_TIMEZONE:
return CATEGORY_DATETIME;
case Types.BOOLEAN:
return CATEGORY_BOOLEAN;
case Types.VARCHAR:
case Types.NVARCHAR:
case Types.LONGVARCHAR:
case Types.LONGNVARCHAR:
case Types.CHAR:
case Types.NCHAR:
return CATEGORY_STRING;
default:
return CATEGORY_OTHER;
}
}
/**
* Represents a database table column.
*/
private static class Column {
/**
* Column label.
*/
private String label;
/**
* Generic SQL type of the column as defined in
*
* java.sql.Types
* .
*/
private int type;
/**
* Generic SQL type name of the column as defined in
*
* java.sql.Types
* .
*/
private String typeName;
/**
* Width of the column that will be adjusted according to column label
* and values to be printed.
*/
private int width = 0;
/**
* Column values from each row of a ResultSet.
*/
private List values = new ArrayList();
/**
* Flag for text justification using String.format.
* Empty string ("") to justify right,
* dash (-) to justify left.
*
* @see #justifyLeft()
*/
private String justifyFlag = "";
/**
* Column type category. The columns will be categorised according
* to their column types and specific needs to print them correctly.
*/
private int typeCategory = 0;
/**
* Constructs a new Column with a column label,
* generic SQL type and type name (as defined in
*
* java.sql.Types
* )
*
* @param label Column label or name
* @param type Generic SQL type
* @param typeName Generic SQL type name
*/
public Column(String label, int type, String typeName) {
this.label = label;
this.type = type;
this.typeName = typeName;
}
/**
* Returns the column label
*
* @return Column label
*/
public String getLabel() {
return label;
}
/**
* Returns the generic SQL type of the column
*
* @return Generic SQL type
*/
public int getType() {
return type;
}
/**
* Returns the generic SQL type name of the column
*
* @return Generic SQL type name
*/
public String getTypeName() {
return typeName;
}
/**
* Returns the width of the column
*
* @return Column width
*/
public int getWidth() {
return width;
}
/**
* Sets the width of the column to width
*
* @param width Width of the column
*/
public void setWidth(int width) {
this.width = width;
}
/**
* Adds a String representation (value)
* of a value to this column object's {@link #values} list.
* These values will come from each row of a
*
* ResultSet
* of a database query.
*
* @param value The column value to add to {@link #values}
*/
public void addValue(String value) {
values.add(value);
}
/**
* Returns the column value at row index i.
* Note that the index starts at 0 so that getValue(0)
* will get the value for this column from the first row
* of a
* ResultSet.
*
* @param i The index of the column value to get
* @return The String representation of the value
*/
public String getValue(int i) {
return values.get(i);
}
/**
* Returns the value of the {@link #justifyFlag}. The column
* values will be printed using String.format and
* this flag will be used to right or left justify the text.
*
* @return The {@link #justifyFlag} of this column
* @see #justifyLeft()
*/
public String getJustifyFlag() {
return justifyFlag;
}
/**
* Sets {@link #justifyFlag} to "-" so that
* the column value will be left justified when printed with
* String.format. Typically numbers will be right
* justified and text will be left justified.
*/
public void justifyLeft() {
this.justifyFlag = "-";
}
/**
* Returns the generic SQL type category of the column
*
* @return The {@link #typeCategory} of the column
*/
public int getTypeCategory() {
return typeCategory;
}
/**
* Sets the {@link #typeCategory} of the column
*
* @param typeCategory The type category
*/
public void setTypeCategory(int typeCategory) {
this.typeCategory = typeCategory;
}
}
}
这是执行此操作的Scala版本...还将以通用方式打印列名称和数据...
def printQuery(res: ResultSet): Unit = {
val rsmd = res.getMetaData
val columnCount = rsmd.getColumnCount
var rowCnt = 0
val s = StringBuilder.newBuilder
while (res.next()) {
s.clear()
if (rowCnt == 0) {
s.append("| ")
for (i <- 1 to columnCount) {
val name = rsmd.getColumnName(i)
s.append(name)
s.append("| ")
}
s.append("\n")
}
rowCnt += 1
s.append("| ")
for (i <- 1 to columnCount) {
if (i > 1)
s.append(" | ")
s.append(res.getString(i))
}
s.append(" |")
System.out.println(s)
}
System.out.println(s"TOTAL: $rowCnt rows")
}
答案 5 :(得分：0)
对于您要执行的操作，您可以使用PreparedStatement而不是Statement。您的代码可能会被修改为 -
String sql = "SELECT column_name from information_schema.columns where table_name='suppliers';";
Statement s = connection.createStatement();
ResultSet rs = s.executeQuery(sql);
希望这有帮助。
答案 6 :(得分：0)
您可以使用 TableSaw library，这是一个很棒的 Java 数据科学/数据框架库。代码很简单：
System.out.println(Table.read().db(resultSet).print());