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, it can be used in a while loop to iterate through the result set. A ResultSet 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 employees");
printf("Number of employees: %s\n", ResultSet_next(r) ? ResultSet_getString(r, 1) : "none");

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.

Date and Time

Result Set provides two principal methods for retrieving temporal column values as C types. ResultSet_getTimestamp() converts a SQL timestamp value to a time_t and ResultSet_getDateTime() returns a tm structure representing a SQL Date, Time, DateTime or Timestamp column type. To get a temporal column value as a string, simply use ResultSet_getString()

A ResultSet is reentrant, but not thread-safe and should only be used by one thread (at the time).

See Also: Connection.h PreparedStatement.h SQLException.h

Macros
#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. More...

Properties
int	ResultSet_getColumnCount (T R)
	Returns the number of columns in this ResultSet object. More...

const char *	ResultSet_getColumnName (T R, int columnIndex)
	Get the designated column's name. More...

long	ResultSet_getColumnSize (T R, int columnIndex)
	Returns column size in bytes. More...

Columns
int	ResultSet_isnull (T R, int columnIndex)
	Returns true if the value of the designated column in the current row of this ResultSet object is SQL NULL, otherwise false. More...

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. More...

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. More...

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. More...

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. More...

long long	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. More...

long long	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. More...

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. More...

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. More...

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. More...

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. More...

Date and Time
time_t	ResultSet_getTimestamp (T R, int columnIndex)
	Retrieves the value of the designated column in the current row of this ResultSet object as a Unix timestamp. More...

time_t	ResultSet_getTimestampByName (T R, const char *columnName)
	Retrieves the value of the designated column in the current row of this ResultSet object as a Unix timestamp. More...

struct tm	ResultSet_getDateTime (T R, int columnIndex)
	Retrieves the value of the designated column in the current row of this ResultSet object as a Date, Time or DateTime. More...

struct tm	ResultSet_getDateTimeByName (T R, const char *columnName)
	Retrieves the value of the designated column in the current row of this ResultSet object as a Date, Time or DateTime. More...

Macro Definition Documentation

#define T ResultSet_T

Typedef Documentation

typedef struct ResultSet_S* T

Function Documentation

int ResultSet_getColumnCount ( T R )

Returns the number of columns in this ResultSet object.

Parameters

R	A ResultSet object

Returns: The number of columns

const char* ResultSet_getColumnName	(	T	R,
		int	columnIndex
	)

Get the designated column's name.

Parameters

R	A ResultSet object
columnIndex	The 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 availability 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

R	A ResultSet object
columnIndex	The first column is 1, the second is 2, ...

Returns: Column data size

Exceptions

SQLException If 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

R	A ResultSet object

Returns: true if the new current row is valid; false if there are no more rows

Exceptions

SQLException If a database access error occurs

int ResultSet_isnull	(	T	R,
		int	columnIndex
	)

Returns true if the value of the designated column in the current row of this ResultSet object is SQL NULL, otherwise false.

If the column value is SQL NULL, a Result Set returns the NULL pointer for string and blob values and 0 for primitive data types. Use this method if you need to differ between SQL NULL and the value NULL/0.

Parameters

R	A ResultSet object
columnIndex	The first column is 1, the second is 2, ...

Returns: True if column value is SQL NULL, otherwise false

Exceptions

SQLException If a database access error occurs or columnIndex is outside the valid range

See Also: SQLException.h

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

R	A ResultSet object
columnIndex	The first column is 1, the second is 2, ...

Returns: The column value; if the value is SQL NULL, the value returned is NULL

Exceptions

SQLException If 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

R	A ResultSet object
columnName	The SQL name of the column. case-sensitive

Returns: The column value; if the value is SQL NULL, the value returned is NULL

Exceptions

SQLException If 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. In general, on both 32 and 64 bits architecture, int is 4 bytes or 32 bits and long long is 8 bytes or 64 bits. A long type is usually equal to int on 32 bits architecture and equal to long long on 64 bits architecture. However, the width of integer types are architecture and compiler dependent. The above is usually true, but not necessarily.

Parameters

R	A ResultSet object
columnIndex	The first column is 1, the second is 2, ...

Returns: The column value; if the value is SQL NULL, the value returned is 0

Exceptions

SQLException If a database access error occurs, columnIndex is outside the valid range or if the value is NaN

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. In general, on both 32 and 64 bits architecture, int is 4 bytes or 32 bits and long long is 8 bytes or 64 bits. A long type is usually equal to int on 32 bits architecture and equal to long long on 64 bits architecture. However, the width of integer types are architecture and compiler dependent. The above is usually true, but not necessarily.

Parameters

R	A ResultSet object
columnName	The SQL name of the column. case-sensitive

Returns: The column value; if the value is SQL NULL, the value returned is 0

Exceptions

SQLException If a database access error occurs, columnName does not exist or if the value is NaN

See Also: SQLException.h

long long 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. In general, on both 32 and 64 bits architecture, int is 4 bytes or 32 bits and long long is 8 bytes or 64 bits. A long type is usually equal to int on 32 bits architecture and equal to long long on 64 bits architecture. However, the width of integer types are architecture and compiler dependent. The above is usually true, but not necessarily.

Parameters

R	A ResultSet object
columnIndex	The first column is 1, the second is 2, ...

Returns: The column value; if the value is SQL NULL, the value returned is 0

Exceptions

SQLException If a database access error occurs, columnIndex is outside the valid range or if the value is NaN

See Also: SQLException.h

long long 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. In general, on both 32 and 64 bits architecture, int is 4 bytes or 32 bits and long long is 8 bytes or 64 bits. A long type is usually equal to int on 32 bits architecture and equal to long long on 64 bits architecture. However, the width of integer types are architecture and compiler dependent. The above is usually true, but not necessarily.

Parameters

R	A ResultSet object
columnName	The SQL name of the column. case-sensitive

Returns: The column value; if the value is SQL NULL, the value returned is 0

Exceptions

SQLException If a database access error occurs, columnName does not exist or if the value is NaN

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

R	A ResultSet object
columnIndex	The 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

SQLException If a database access error occurs, columnIndex is outside the valid range or if the value is NaN

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

R	A ResultSet object
columnName	The SQL name of the column. case-sensitive

Returns: The column value; if the value is SQL NULL, the value returned is 0.0

Exceptions

SQLException If a database access error occurs, columnName does not exist or if the value is NaN

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

R	A ResultSet object
columnIndex	The first column is 1, the second is 2, ...
size	The 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

SQLException If 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

R	A ResultSet object
columnName	The SQL name of the column. case-sensitive
size	The 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

SQLException If a database access error occurs or columnName does not exist

See Also: SQLException.h

time_t ResultSet_getTimestamp	(	T	R,
		int	columnIndex
	)

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

The returned value is in Coordinated Universal Time (UTC) and represent seconds since the epoch (January 1, 1970, 00:00:00 GMT).

Even though the underlying database might support timestamp ranges before the epoch and after '2038-01-19 03:14:07 UTC' it is safest not to assume or use values outside this range. Especially on a 32-bits system.

SQLite does not have temporal SQL data types per se and using this method with SQLite assume the column value in the Result Set to be either a numerical value representing a Unix Time in UTC which is returned as-is or an ISO 8601 time string which is converted to a time_t value. See also PreparedStatement_setTimestamp()

Parameters

R	A ResultSet object
columnIndex	The first column is 1, the second is 2, ...

Returns: The column value as seconds since the epoch in the GMT timezone. If the value is SQL NULL, the value returned is 0, i.e. January 1, 1970, 00:00:00 GMT

Exceptions

SQLException If a database access error occurs, if columnIndex is outside the range [1..ResultSet_getColumnCount()] or if the column value cannot be converted to a valid timestamp

See Also: SQLException.h PreparedStatement_setTimestamp

time_t ResultSet_getTimestampByName	(	T	R,
		const char *	columnName
	)

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

The returned value is in Coordinated Universal Time (UTC) and represent seconds since the epoch (January 1, 1970, 00:00:00 GMT).

Even though the underlying database might support timestamp ranges before the epoch and after '2038-01-19 03:14:07 UTC' it is safest not to assume or use values outside this range. Especially on a 32-bits system.

SQLite does not have temporal SQL data types per se and using this method with SQLite assume the column value in the Result Set to be either a numerical value representing a Unix Time in UTC which is returned as-is or an ISO 8601 time string which is converted to a time_t value. See also PreparedStatement_setTimestamp()

Parameters

R	A ResultSet object
columnName	The SQL name of the column. case-sensitive

Returns: The column value as seconds since the epoch in the GMT timezone. If the value is SQL NULL, the value returned is 0, i.e. January 1, 1970, 00:00:00 GMT

Exceptions

SQLException If a database access error occurs, if columnName is not found or if the column value cannot be converted to a valid timestamp

See Also: SQLException.h PreparedStatement_setTimestamp

struct tm ResultSet_getDateTime	(	T	R,
		int	columnIndex
	)

Retrieves the value of the designated column in the current row of this ResultSet object as a Date, Time or DateTime.

This method can be used to retrieve the value of columns with the SQL data type, Date, Time, DateTime or Timestamp. The returned tm structure follows the convention for usage with mktime(3) where, tm_hour = hours since midnight [0-23], tm_min = minutes after the hour [0-59], tm_sec = seconds after the minute [0-60], tm_mday = day of the month [1-31] and tm_mon = months since January [0-11]. If the column value contains timezone information, tm_gmtoff is set to the offset from UTC in seconds, otherwise tm_gmtoff is set to 0. On systems without tm_gmtoff, (Solaris), the member, tm_wday is set to gmt offset instead as this property is ignored by mktime on input. The exception to the above is tm_year which contains the year literal and not years since 1900 which is the convention. All other fields in the structure are set to zero. If the column type is DateTime or Timestamp all the fields mentioned above are set, if it is a Date or Time, only the relevant fields are set.

Parameters

R	A ResultSet object
columnIndex	The first column is 1, the second is 2, ...

Returns: A tm structure with fields for date and time. If the value is SQL NULL, a zeroed tm structure is returned

Exceptions

SQLException If a database access error occurs, if columnIndex is outside the range [1..ResultSet_getColumnCount()] or if the column value cannot be converted to a valid SQL Date, Time or DateTime type

See Also: SQLException.h

struct tm ResultSet_getDateTimeByName	(	T	R,
		const char *	columnName
	)

Retrieves the value of the designated column in the current row of this ResultSet object as a Date, Time or DateTime.

This method can be used to retrieve the value of columns with the SQL data type, Date, Time, DateTime or Timestamp. The returned tm structure follows the convention for usage with mktime(3) where, tm_hour = hours since midnight [0-23], tm_min = minutes after the hour [0-59], tm_sec = seconds after the minute [0-60], tm_mday = day of the month [1-31] and tm_mon = months since January [0-11]. If the column value contains timezone information, tm_gmtoff is set to the offset from UTC in seconds, otherwise tm_gmtoff is set to 0. On systems without tm_gmtoff, (Solaris), the member, tm_wday is set to gmt offset instead as this property is ignored by mktime on input. The exception to the above is tm_year which contains the year literal and not years since 1900 which is the convention. All other fields in the structure are set to zero. If the column type is DateTime or Timestamp all the fields mentioned above are set, if it is a Date or Time, only the relevant fields are set.

Parameters

R	A ResultSet object
columnName	The SQL name of the column. case-sensitive

Returns: A tm structure with fields for date and time. If the value is SQL NULL, a zeroed tm structure is returned

Exceptions

SQLException If a database access error occurs, if columnName is not found or if the column value cannot be converted to a valid SQL Date, Time or DateTime type

See Also: SQLException.h

Detailed Description

Example

Automatic type conversions

Date and Time

Macros

Typedefs

Functions

Macro Definition Documentation

Typedef Documentation

Function Documentation