SQLDA Data Structure

The SQLDA data structure definition (from SQLDA.H) looks like this:

// SQL Descriptor Area - SQLDA

struct sqlda

unsigned char sqldaid[8];

// Eye catcher = 'SQLDA  '

long sqldabc;

// SQLDA size in bytes = 16+44*SQLN

short sqln;

// Number of SQLVAR elements

short sqld;

// Num of used SQLVAR elements

struct sqlvar

   short sqltype;

// Variable datatype

   short sqllen;

// Variable data length

   unsigned char FAR

      *sqldata;

// Pointer to variable data value

   short FAR *sqlind;

// Pointer to null indicator

   struct sqlname

// Variable name

      short length;

// Name length [1..30]

      unsigned char

         data[30];

// Variable or column name

   } sqlname;

} sqlvar[1];

};

SQLDA

Fields and datatypes for the SQLDA data structure are described in the following table.


Field and datatype	Contains

sqldaid
unsigned char*	The text string SQLDA. This field is not used for FETCH, OPEN, or EXECUTE statements.
sqldabc
long	The length of the SQLDA data structure (sqln* 44 + 16).
sqln
short	The total number of sqlvar entries that are allocated; equal to the number of input parameters or output columns.
sqld
short	The number of sqlvar entries that are used.
sqlvar
struct	The values that are listed in the sqlvar table; the values can occur several times, listed once per column in the results set or input parameter.
sqltype
short	The number that represents the datatype of columns or host variables, and that indicates whether null values are allowed. For valid values, see "Valid Values for sqltype," later in this chapter.
sqllen
short	The external length of a value from a column.
sqldata
unsigned char far*	The address of the host variable (which must be inserted by the application) for FETCH, OPEN, and EXECUTE statements. For DESCRIBE and PREPARE statements, sqldata is not used.
sqlind
short far*	The address of an indicator variable for FETCH, OPEN, and EXECUTE statements, if one exists.
	If the column does not permit a null value, the field is undefined. If the column permits a null value, sqlind is set to –1 if the data value is null or to 0 if the data value is not null. For DESCRIBE and PREPARE statements, sqlind is not used.
sqlname
struct	The name and length of the column. (Is not used for FETCH, OPEN, and EXECUTE statements.)
length
short	The length of the name column.
name
unsigned char*	The name of the column. For a derived column, this field contains the ASCII numeric literal value that represents the derived column's original position within the select list.

Valid Values for sqltype

The following table lists the values for the sqltype field in SQLDA data structure and corresponding SQL Server datatypes for which they can serve as host variables in a FETCH statement or and EXECUTE statement. For each pair of sqltype codes, the odd number type signifies a host variable with a corresponding null indicator variable needed for setting or retrieving null values.


Sqltype code	Datatype description	Corresponding SQL Server datatype	Sample declaration

392/393	26-byte date & time char format corresponds to the formats supported by dbconvert for datetime to/from char (See "Programming DB-Library for C")	datetime, smalldatetime	char date1[27] = "Mar 7 1988 7:12PM";
444/445	Binary	binary, varbinary, image, timestamp Note: sqltype 444/445 is automatically used for these SQL Server column types on output.	char binary1[4097];
452/453	Char string <=254 bytes; not automatically null terminated Note: Make sure you initialize the full array with nulls when using this type for output.	char, varchar, or text	char mychar[255];
456/457	Length-prefixed long character field; not automatically null terminated	char, varchar, or text	struct TEXTVAR { short len; char data[4097]; } textvar;
462/463	Null-terminated string Note: Declarations of known length (mychar1) will be padded with blanks and a terminating null. Declarations of char pointers (mychar2) will not be blank padded and the application program must ensure sufficient space is allocated.	char, varchar, or text.	char mychar1[41]; char * mychar2;
480/481	8-byte floating point	float, real, int, smallint, tinyint, decimal, numeric, money, smallmoney	double mydouble1;
482/483	4-byte floating point	float, real, int, smallint, tinyint, decimal, numeric, money, smallmoney	float myfloat1;
496/497	4-byte integer	int, smallint, tinyint, bit	long myint1;
500/501	2-byte integer	smallint, tinyint, bit	short myshort1;

When using SQLDAs in a DESCRIBE or PREPARE INTO, the following datatype codes are returned.


SQL Server column	sqltype returned by DESCRIBE or PREPARE INTO	Comments

char, varchar	452/453	452/453 is a Cobol char datatype, not null terminated. Easier to use 462/463 from C.
text	456/457	sqllen set to max of 32767 for text
binary, varbinary, image, timestamp	444/445	sqllen set to max of 32767 for image
smallint, tinyint, bit	500/501
int	496/497
float	480/481
real	482/483
datetime, smalldatetime	392/393
decimal, numeric, money, smallmoney	484/485	Cobol decimal format; not supported for FETCH or EXECUTE in ESQL/C (use 480 or 482 instead). sqllen encoded with scale and precision; use sqllen &= 0xFF to get just precision.

DESCRIBE and PREPARE INTO are only supported for output columns of SELECT statements. They are not supported for INSERT, UPDATE, or DELETE statements, or for any statement requiring an input host variable.