Defines | Typedefs | Functions
ResultSet.h File Reference

Detailed Description

A ResultSet represents a database result set.

A ResultSet is created by executing a SQL SELECT statement using either Connection_executeQuery() or PreparedStatement_executeQuery().

A ResultSet maintains a cursor pointing to its current row of data. Initially the cursor is positioned before the first row. ResultSet_next() moves the cursor to the next row, and because it returns false when there are no more rows in the ResultSet object, it can be used in a while loop to iterate through the result set. A ResultSet object is not updatable and has a cursor that moves forward only. Thus, you can iterate through it only once and only from the first row to the last row.

The ResultSet interface provides getter methods for retrieving column values from the current row. Values can be retrieved using either the index number of the column or the name of the column. In general, using the column index will be more efficient. Columns are numbered from 1.

Column names used as input to getter methods are case sensitive. When a getter method is called with a column name and several columns have the same name, the value of the first matching column will be returned. The column name option is designed to be used when column names are used in the SQL query that generated the result set. For columns that are NOT explicitly named in the query, it is best to use column indices.

Example

The following examples demonstrate how to obtain a ResultSet and how to get values from the set:

 ResultSet_T r = Connection_executeQuery(con, "SELECT ssn, name, picture FROM employees");
 while (ResultSet_next(r)) 
 {
      int ssn = ResultSet_getIntByName(r, "ssn");
      const char *name =  ResultSet_getStringByName(r, "name");
      int pictureSize;
      const void *picture = ResultSet_getBlobByName(r, "picture", &pictureSize);
      [..]
 }
 

Here is another example where a generated result is selected and printed:

 ResultSet_T r = Connection_executeQuery(con, "SELECT count(*) FROM users");
 printf("Number of users: %s\n", ResultSet_next(r) ? ResultSet_getString(r, 1) : "no users");
 

Automatic type conversions

A ResultSet store values internally as bytes and convert values on-the-fly to numeric types when requested, such as when ResultSet_getInt() or one of the other numeric get-methods are called. In the above example, even if count(*) returns a numeric value, we can use ResultSet_getString() to get the number as a string or if we choose, we can use ResultSet_getInt() to get the value as an integer. In the latter case, note that if the column value cannot be converted to a number, an SQLException is thrown.

See also:
Connection.h PreparedStatement.h SQLException.h

Defines

#define T   ResultSet_T

Typedefs

typedef struct ResultSet_S * T

Functions

int ResultSet_next (T R)
 Moves the cursor down one row from its current position.
const char * ResultSet_getString (T R, int columnIndex)
 Retrieves the value of the designated column in the current row of this ResultSet object as a C-string.
const char * ResultSet_getStringByName (T R, const char *columnName)
 Retrieves the value of the designated column in the current row of this ResultSet object as a C-string.
int ResultSet_getInt (T R, int columnIndex)
 Retrieves the value of the designated column in the current row of this ResultSet object as an int.
int ResultSet_getIntByName (T R, const char *columnName)
 Retrieves the value of the designated column in the current row of this ResultSet object as an int.
long long int ResultSet_getLLong (T R, int columnIndex)
 Retrieves the value of the designated column in the current row of this ResultSet object as a long long.
long long int ResultSet_getLLongByName (T R, const char *columnName)
 Retrieves the value of the designated column in the current row of this ResultSet object as a long long.
double ResultSet_getDouble (T R, int columnIndex)
 Retrieves the value of the designated column in the current row of this ResultSet object as a double.
double ResultSet_getDoubleByName (T R, const char *columnName)
 Retrieves the value of the designated column in the current row of this ResultSet object as a double.
const void * ResultSet_getBlob (T R, int columnIndex, int *size)
 Retrieves the value of the designated column in the current row of this ResultSet object as a void pointer.
const void * ResultSet_getBlobByName (T R, const char *columnName, int *size)
 Retrieves the value of the designated column in the current row of this ResultSet object as a void pointer.
Properties
int ResultSet_getColumnCount (T R)
 Returns the number of columns in this ResultSet object.
const char * ResultSet_getColumnName (T R, int columnIndex)
 Get the designated column's name.
long ResultSet_getColumnSize (T R, int columnIndex)
 Returns column size in bytes.

Define Documentation

#define T   ResultSet_T

Typedef Documentation

typedef struct ResultSet_S* T

Function Documentation

Returns the number of columns in this ResultSet object.

Parameters:
RA ResultSet object
Returns:
The number of columns
const char* ResultSet_getColumnName ( T  R,
int  columnIndex 
)

Get the designated column's name.

Parameters:
RA ResultSet object
columnIndexThe first column is 1, the second is 2, ...
Returns:
Column name or NULL if the column does not exist. You should use the method ResultSet_getColumnCount() to test for the availablity of columns in the result set.
long ResultSet_getColumnSize ( T  R,
int  columnIndex 
)

Returns column size in bytes.

If the column is a blob then this method returns the number of bytes in that blob. No type conversions occur. If the result is a string (or a number since a number can be converted into a string) then return the number of bytes in the resulting string.

Parameters:
RA ResultSet object
columnIndexThe first column is 1, the second is 2, ...
Returns:
Column data size
Exceptions:
SQLExceptionif columnIndex is outside the valid range
See also:
SQLException.h
int ResultSet_next ( T  R)

Moves the cursor down one row from its current position.

A ResultSet cursor is initially positioned before the first row; the first call to this method makes the first row the current row; the second call makes the second row the current row, and so on. When there are not more available rows false is returned. An empty ResultSet will return false on the first call to ResultSet_next().

Parameters:
RA ResultSet object
Returns:
true if the new current row is valid; false if there are no more rows
const char* ResultSet_getString ( T  R,
int  columnIndex 
)

Retrieves the value of the designated column in the current row of this ResultSet object as a C-string.

If columnIndex is outside the range [1..ResultSet_getColumnCount()] this method throws an SQLException. The returned string may only be valid until the next call to ResultSet_next() and if you plan to use the returned value longer, you must make a copy.

Parameters:
RA ResultSet object
columnIndexThe first column is 1, the second is 2, ...
Returns:
The column value; if the value is SQL NULL, the value returned is NULL
Exceptions:
SQLExceptionif a database access error occurs or columnIndex is outside the valid range
See also:
SQLException.h
const char* ResultSet_getStringByName ( T  R,
const char *  columnName 
)

Retrieves the value of the designated column in the current row of this ResultSet object as a C-string.

If columnName is not found this method throws an SQLException. The returned string may only be valid until the next call to ResultSet_next() and if you plan to use the returned value longer, you must make a copy.

Parameters:
RA ResultSet object
columnNameThe SQL name of the column. case-sensitive
Returns:
The column value; if the value is SQL NULL, the value returned is NULL
Exceptions:
SQLExceptionif a database access error occurs or columnName does not exist
See also:
SQLException.h
int ResultSet_getInt ( T  R,
int  columnIndex 
)

Retrieves the value of the designated column in the current row of this ResultSet object as an int.

If columnIndex is outside the range [1..ResultSet_getColumnCount()] this method throws an SQLException.

Parameters:
RA ResultSet object
columnIndexThe first column is 1, the second is 2, ...
Returns:
The column value; if the value is SQL NULL, the value returned is 0
Exceptions:
SQLExceptionif a database access error occurs or columnIndex is outside the valid range
See also:
SQLException.h
int ResultSet_getIntByName ( T  R,
const char *  columnName 
)

Retrieves the value of the designated column in the current row of this ResultSet object as an int.

If columnName is not found this method throws an SQLException.

Parameters:
RA ResultSet object
columnNameThe SQL name of the column. case-sensitive
Returns:
The column value; if the value is SQL NULL, the value returned is 0
Exceptions:
SQLExceptionif a database access error occurs or columnName does not exist
See also:
SQLException.h
long long int ResultSet_getLLong ( T  R,
int  columnIndex 
)

Retrieves the value of the designated column in the current row of this ResultSet object as a long long.

If columnIndex is outside the range [1..ResultSet_getColumnCount()] this method throws an SQLException.

Parameters:
RA ResultSet object
columnIndexThe first column is 1, the second is 2, ...
Returns:
The column value; if the value is SQL NULL, the value returned is 0
Exceptions:
SQLExceptionif a database access error occurs or columnIndex is outside the valid range
See also:
SQLException.h
long long int ResultSet_getLLongByName ( T  R,
const char *  columnName 
)

Retrieves the value of the designated column in the current row of this ResultSet object as a long long.

If columnName is not found this method throws an SQLException.

Parameters:
RA ResultSet object
columnNameThe SQL name of the column. case-sensitive
Returns:
The column value; if the value is SQL NULL, the value returned is 0
Exceptions:
SQLExceptionif a database access error occurs or columnName does not exist
See also:
SQLException.h
double ResultSet_getDouble ( T  R,
int  columnIndex 
)

Retrieves the value of the designated column in the current row of this ResultSet object as a double.

If columnIndex is outside the range [1..ResultSet_getColumnCount()] this method throws an SQLException.

Parameters:
RA ResultSet object
columnIndexThe first column is 1, the second is 2, ...
Returns:
The column value; if the value is SQL NULL, the value returned is 0.0
Exceptions:
SQLExceptionif a database access error occurs or columnIndex is outside the valid range
See also:
SQLException.h
double ResultSet_getDoubleByName ( T  R,
const char *  columnName 
)

Retrieves the value of the designated column in the current row of this ResultSet object as a double.

If columnName is not found this method throws an SQLException.

Parameters:
RA ResultSet object
columnNameThe SQL name of the column. case-sensitive
Returns:
The column value; if the value is SQL NULL, the value returned is 0.0
Exceptions:
SQLExceptionif a database access error occurs or columnName does not exist
See also:
SQLException.h
const void* ResultSet_getBlob ( T  R,
int  columnIndex,
int *  size 
)

Retrieves the value of the designated column in the current row of this ResultSet object as a void pointer.

If columnIndex is outside the range [1..ResultSet_getColumnCount()] this method throws an SQLException. The returned blob may only be valid until the next call to ResultSet_next() and if you plan to use the returned value longer, you must make a copy.

Parameters:
RA ResultSet object
columnIndexThe first column is 1, the second is 2, ...
sizeThe number of bytes in the blob is stored in size
Returns:
The column value; if the value is SQL NULL, the value returned is NULL
Exceptions:
SQLExceptionif a database access error occurs or columnIndex is outside the valid range
See also:
SQLException.h
const void* ResultSet_getBlobByName ( T  R,
const char *  columnName,
int *  size 
)

Retrieves the value of the designated column in the current row of this ResultSet object as a void pointer.

If columnName is not found this method throws an SQLException. The returned blob may only be valid until the next call to ResultSet_next() and if you plan to use the returned value longer, you must make a copy.

Parameters:
RA ResultSet object
columnNameThe SQL name of the column. case-sensitive
sizeThe number of bytes in the blob is stored in size
Returns:
The column value; if the value is SQL NULL, the value returned is NULL
Exceptions:
SQLExceptionif a database access error occurs or columnName does not exist
See also:
SQLException.h

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