ct_compute_info

Description

Retrieve compute result information.

Syntax

CS_RETCODE ct_compute_info(cmd, type, colnum, buffer,
                 buflen, outlen)
 CS_COMMAND      *cmd;
 CS_INT                    type;
 CS_INT                   colnum;
 CS_VOID                *buffer;
 CS_INT                    buflen;
 CS_INT                   *outlen;

Parameters

cmd

A pointer to the CS_COMMAND structure managing a client/server command.

type

The type of information to return. For a list of the symbolic values for type, see Table 3-10.

colnum

The number of the compute column of interest, as it appears in the compute row result set. Compute columns appear in the order in which they are listed in the compute clause of a select statement. The first column is number 1, the second is number 2, and so forth.

buffer

A pointer to the space in which ct_compute_info will place the requested information.

If buflen indicates that *buffer is not large enough to hold the requested information, ct_compute_info returns CS_FAIL.

buflen

The length, in bytes, of the *buffer data space or CS_UNUSED if *buffer represents a fixed-length or symbolic value.

outlen

A pointer to an integer variable.

Returns

ct_compute_info returns the following values:

Examples

Example 1

Assume that the following command has been executed:

select dept, name, year, sales from employee 

           order by dept, name, year 

           compute count(name) by dept, name

1. The call:

   CS_INT      mybuffer;
   

   ct_compute_info(cmd, CS_BYLIST_LEN, CS_UNUSED,
   

           &mybuffer, CS_UNUSED, CS_UNUSED);
   

   sets mybuffer to 2, because there are two items in the bylist.

2. The call:

   CS_SMALLINT    mybuffer[2];
   

    CS_INT         outlength;
   

   ct_compute_info(cmd, CS_COMP_BYLIST, CS_UNUSED,
   

            mybuffer, sizeof(mybuffer), &outlength)
   

   copies the CS_SMALLINT values 1 and 2 into mybuffer[0] and mybuffer[1] to indicate that the bylist is composed of columns 1 and 2 from the select list.

3. The call:

   CS_INT      mybuffer;
   

   ct_compute_info(cmd, CS_COMP_COLID, 1, &mybuffer,
   

           CS_UNUSED,NULL);
   

   sets mybuffer to 2, since name is the second column in the select list.

4. The call:

   CS_INT     mybuffer;
   

   ct_compute_info(cmd, CS_COMP_ID, CS_UNUSED,
   

            &mybuffer, CS_UNUSED, NULL);
   

   sets mybuffer to 1 because there is only a single compute clause in the select statement.

5. The call:

   CS_INT    mybuffer;
   

   ct_compute_info(cmd, CS_COMP_OP, 1, &mybuffer,
   

           CS_UNUSED, NULL);
   

   sets mybuffer to the symbolic value CS_OP_COUNT, since the aggregate operator for the first compute column is a count.

Usage

Table 3-10 summarizes ct_compute_info usage.

• Compute rows result from the compute clause of a select statement. A compute clause generates a compute row every time the value of its by column-list changes. A compute row contains one column for each aggregate operator in the compute clause. If a select statement contains multiple compute clauses, separate compute rows are generated by each clause.

  Each compute row returned by the server is considered to be a distinct result set. That is, each result set of type CS_COMPUTE_RESULT will contain exactly one row.

• It is only legal to call ct_compute_info when compute information is available; that is, after ct_results returns CS_COMPUTE_RESULT or CS_COMPUTEFMT.

• Each section below contains information about a particular type of compute result information.

The bylist for a compute row

• A select statement’s compute clause may contain the keyword by, followed by a list of columns. This list, known as the bylist, divides the results into subgroups, based on changing values in the specified columns. The compute clause’s aggregate operators are applied to each subgroup, generating a compute row for each subgroup.

The select-list column ID for a compute column

• The select-list column ID for a compute column is the position within the select-list of the column from which the compute column derives.

The compute ID for a compute row

• A SQL select statement can have multiple compute clauses, each of which returns a separate compute row. The compute ID corresponding to the first compute clause in a select statement is 1.

The aggregate operator for a particular compute row column

• When called with type as CS_COMP_OP, ct_compute_info sets *buffer to one of the following aggregate operator types:

  Table 3-11: Aggregate operator types

  *buffer setting	Meaning
  CS_OP_AVG	Average aggregate operator
  CS_OP_COUNT	Count aggregate operator
  CS_OP_MAX	Maximum aggregate operator
  CS_OP_MIN	Minimum aggregate operator
  CS_OP_SUM	Sum aggregate operator.

See also

ct_bind, ct_describe, ct_res_info, ct_results

---

Copyright © 2003. Sybase Inc. All rights reserved.

View this book as PDF