16.20 - PrepInfo - Teradata Tools and Utilities

Teradata® Call-Level Interface Version 2 Reference for Mainframe-Attached Systems

prodname
Teradata Tools and Utilities
vrm_release
16.20
created_date
September 2019
category
Programming Reference
featnum
B035-2417-108K

Purpose

Returns a description of the return data specified by a request, when that request is sent to the Teradata Database with a Request-processing-option of Prepare and a Response-mode of Indicator.

The parcel also contains an estimate of the time it will take to execute the statement.

Usage Notes

If the PrepInfo parcel contains zeros, the statement was an ECHO statement. The PrepInfo parcel is generated by the Teradata Database.

Parcel Data

The following information applies to the PrepInfo parcel.

Flavor Parcel Body Length Parcel Body Fields
86 12 to maximum body size CostEstimate: 8 byte floating

SummaryCount:

2 byte unsigned integer

The following occur once for the SELECTed columns, and SummaryCount times for any WITH clauses.
ColumnCount: 2 byte unsigned integer
     For each column, the following occur:
     DataType: 2 byte unsigned integer

     DataLen:

2 byte unsigned integer

     ColumnName:

two byte unsigned integer plus the number of bytes specified by that integer

     ColumnFormat:

two byte unsigned integer plus the number of bytes specified by that integer

     ColumnTitle:

two byte unsigned integer plus the number of bytes specified by that integer

Field Notes

The following notes apply to PrepInfo fields.

  • CostEstimate returns a time estimate, in milliseconds, of how long it will take to execute a request.

    The CostEstimate field is set to zero if the estimated time is negligible.

  • SummaryCount specifies the number of WITH clauses in the request.

    The SummaryCount field is set to zero if no summary data is returned, that is, if the request is not a SELECT statement or if the request is a SELECT statement without any WITH clauses.

  • ColumnCount specifies how many sets of column-descriptive fields follow.

    The first occurrence of ColumnCount indicates the number of columns returned by the statement.

    It is immediately followed by as many sets of the column-descriptive fields as required to describe each column.

    Next, if SummaryCount is greater than zero, a group of fields is returned once for each WITH clause.

    Each group comprises a ColumnCount field that indicates the number of columns referenced in the clause, and as many sets of the column-descriptive fields as required to describe each column in that clause:

    • DataType specifies a code associated with a column‘s data type. See Data Type for the possible data types.
    • DataLen specifies a column‘s length in bytes.

      However, if a column‘s data type is DECIMAL, the first byte contains the integral digits and the second byte contains the fractional digits.

    • ColumnName specifies a column‘s name, consisting of length in bytes of the name followed by that name in characters from the current session character set. The maximum length of a name currently may be obtained using the DBCHQE SQL-limits query, though in the future the maximum might increase to allow character representation information. The absolute maximum is 65535.

      If a column is the result of an expression, the first two bytes contain a length of zero and the text portion of the field is empty.

    • ColumnFormat specifies a column‘s format, consisting of length in bytes of the Format followed by that Format in characters from the current session character set. The maximum length is not externally provided by the Database so the only limit available is 65535.

      If a column‘s format is null, the first two bytes contain a length of zero and the text portion of the field is empty.

    • ColumnTitle specifies a column‘s title, consisting of length in bytes of the Title followed by that Title in characters from the current session character set. The maximum length is not externally provided by the Database so the only limit available is 65535.

      If a column‘s title is null, the first two bytes contain a length of zero and the text portion of the field is empty, when Return-statement-info 'Y' was not specified.

For example, consider the following SELECT statement,

SELECT Name
FROM Employee
WITH COUNT (DeptNo), SUM (Salary) BY Salary
WITH COUNT (DeptNo) BY DeptNo;

This statement produces a PrepInfo parcel with the following byte sequence:

Parcel flavor is 86 with length 124
40 4D BE B8 51 EB 85 1E 00 02 00 01 01 C0 00 0C
00 04 D5 81 94 85 00 05 E7 4D F1 F2 5D 00 04 4E
61 6D 65 00 02 01 F1 00 04 00 00 00 06 60 4D F1
F0 5D F9 00 0B E2 E4 D4 4D C4 85 97 A3 D5 96 5D
01 E5 0F 02 00 00 00 0A E9 E9 E9 6B E9 E9 F9 4B
F9 F9 00 0B 53 75 6D 28 53 61 6C 61 72 79 29 00
01 01 F1 00 04 00 00 00 06 E2 E4 D4 4D E2 81 93
81 99 A8 5D 00 0B E2 E4 D4 4D C4 85 97 A3 D5 96
5D

The parcel fields, above, translate as follows (an explanation of each acronym follows):

CE CE CE CE CE CE CE CE SC SC CC CC DT DT DL DL
NL NL CN CN CN CN FL FL CF CF CF CF CF TL TL CT
CT CT CT CC CC DT DT DL DL NL NL FL FL CF CF CF
CF CF CF TL TL CT CT CT CT CT CT CT CT CT CT CT
DT DT DL DL NL NL FL FL CF CF CF CF CF CF CF CF
CF CF TL TL CT CT CT CT CT CT CT CT CT CT CT CC
CC DT DT DL DL NL NL FL FL CF CF CF CF CF CF TL
TL CT CT CT CT CT CT CT CT CT CT CT
CostEstimate = CE, 8 bytes
SummaryCount = SCxx, where xx is the number of WITH clauses, 2 bytes
ColumnCount = CCxx, where xx is the number of columns, 2 bytes
DataType = DT, 2 bytes
DataLength = DL, 2 bytes
ColumnName = NLxx followed by CN, where xx indicates the field‘s length and CN represents the text
ColumnFormat = FLxx followed by CF, where xx indicates the field‘s length and CF represents the text
ColumnTitle = TLxx followed by CT, where xx indicates the field‘s length and CT represents the text