Open Client Client-Library/C Reference Manual

Usage

Table 3-10 summarizes ct_compute_info usage.

Summary of ct_compute_info parameters
Value of type	Value of colnum	Information retrieved	*buffer is set to	*outlen is set to
CS_BYLIST_LEN	CS_UNUSED	The number of elements in the bylist array	An integer valu.	sizeof(CS_INT)
CS_COMP_BYLIST	CS_UNUSED	An array containing the bylist that produced this compute row	An array of CS_SMALLINT values	The length of the array, in bytes
CS_COMP_COLID	The column number of the compute column	The select-list column ID of the column from which the compute column derives	An integer value	sizeof(CS_INT)
CS_COMP_ID	CS_UNUSED	The compute ID for the current compute row	An integer value	sizeof(CS_INT)
CS_COMP_OP	The column number of the compute column	The aggregate operator type for the compute column	One of the following symbolic values: CS_OP_SUM CS_OP_AVG CS_OP_COUNT CS_OP_MIN CS_OP_MAX	sizeof(CS_INT)

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:


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