DESCRIBE TABLE

The DESCRIBE TABLE statement obtains information about a table or view.

This statement can only be embedded in an application program, SQL function, SQL procedure, or trigger. It is an executable statement that cannot be dynamically prepared. It must not be specified in Java™.

Authorization

The privileges held by the authorization ID of the statement must include at least one of the following:

For the table or view identified in the statement:
- The system authority of *OBJOPR on the table or view
- The system authority *EXECUTE on the library containing the table or view
Administrative authority

Syntax

>>-DESCRIBE TABLE--variable------------------------------------->
 
            .-SQL-.              .-LOCAL--.
>--+-USING--+-----+--DESCRIPTOR--+--------+--SQL-descriptor-name-+-><
   |                             '-GLOBAL-'                      |
   '-INTO----descriptor-name----+-------------------------+------'
                                '-USING--+-NAMES--------+-'
                                         +-SYSTEM NAMES-+
                                         +-LABELS-------+
                                         +-ANY----------+
                                         +-BOTH---------+
                                         '-ALL----------'

Description

variable

Identifies the table or view to describe. When the DESCRIBE TABLE statement is executed:

The name must identify a table or view that exists at the application server.
The variable must be a character-string or UTF-16 or UCS-2 graphic-string variable and must not include an indicator variable.
The table name that is contained within the variable must be left-justified and must be padded on the right with blanks if its length is less than that of the variable.
The name of the table must be in uppercase unless it is a delimited name.

When the DESCRIBE TABLE statement is executed, the database manager assigns values to the variables of the SQL descriptor or SQLDA as follows:

USING

Identifies an SQL descriptor.

LOCAL: Specifies the scope of the name of the descriptor to be local to program invocation.
GLOBAL: Specifies the scope of the name of the descriptor to be global to the SQL session.
SQL-descriptor-name: Names the SQL descriptor. The name must identify a descriptor that already exists with the specified scope.

INTO descriptor-name

Identifies an SQL descriptor area (SQLDA), which is described in Appendix D. SQLDA (SQL descriptor area). Before the DESCRIBE TABLE statement is executed, the following variable in the SQLDA must be set.

SQLN: Specifies the number of SQLVAR occurrences provided in the SQLDA. SQLN must be set to a value greater than or equal to zero before the DESCRIBE TABLE statement is executed. For information on techniques to determine the number of occurrences requires, see Determining how many SQLVAR occurrences are needed.

The rules for REXX are different. For more information, see the Embedded SQL Programming book.

When the DESCRIBE statement is executed, the database manager assigns values to the variables of the SQLDA as follows:

SQLDAID

The first 6 bytes are set to 'SQLDA ' (that is, 5 letters followed by the space character).

The seventh byte is set based on the column described:

If the SQLDA contains two, three, or four SQLVAR entries for every column of the table, the seventh byte is set to '2', '3', or '4'. This technique is used in order to accommodate LOB or distinct type result columns, labels, and system names.
Otherwise, the seventh byte is set to the space character.

The seventh byte is set to the space character if there is not enough room in the SQLDA to contain the description of all columns.

The eighth byte is set to the space character.

SQLDABC

Length of the SQLDA in bytes.

SQLD

The number of columns in the table.

SQLVAR

If the value of SQLD is 0, or greater than the value of SQLN, no values are assigned to occurrences of SQLVAR.

If the value of SQLD is n, where n is greater than 0 but less than or equal to the value of SQLN, values are assigned to the first n occurrences of SQLVAR so that the first occurrence of SQLVAR contains a description of the first column of the table, the second occurrence of SQLVAR contains a description of the second column of the table, and so on. For information on the values assigned to SQLVAR occurrences, see Field descriptions in an occurrence of SQLVAR.

USING

Specifies what value to assign to each SQLNAME variable in the SQLDA. If the requested value does not exist or if the length of a name is greater than 30, SQLNAME is set to a length of 0.

NAMES: Assigns the name of the column. The column name returned is case sensitive and without delimiters. This is the default.
SYSTEM NAMES: Assigns the system column name of the column.
LABELS: Assigns the label of the column. (Column labels are defined by the LABEL statement.) Only the first 20 bytes of the label are returned.
ANY: Assigns the column label. If the column has no label, the column name is used instead.
BOTH: Assigns both the label and name of the column. In this case, two or three occurrences of SQLVAR per column, depending on whether the table contains distinct types, are needed to accommodate the additional information. To specify this expansion of the SQLVAR array, set SQLN to 2*n or 3*n(where n is the number of columns in the table or view). The first n occurrences of SQLVAR contain the column names if they are different from the system column name. Either the second or third n occurrences contain the column labels. If there are no distinct types, the labels are returned in the second set of SQLVAR entries. Otherwise, the labels are returned in the third set of SQLVAR entries.
ALL: Assigns the label, column name, and system column name. In this case three or four occurrences of SQLVAR per column, depending on whether the table contains distinct types, are needed to accommodate the additional information. To specify this expansion of the SQLVAR array, set SQLN to 3*n or 4*n (where n is the number of columns in the table). The first n occurrences of SQLVAR contain the system column names. The second or third n occurrences contain the column labels. The third or fourth n occurrences contain the column names. If there are no distinct types, the labels are returned in the second set of SQLVAR entries and the column names are returned in the third set of SQLVAR entries. Otherwise, the labels are returned in the third set of SQLVAR entries and the column names are returned in the fourth set of SQLVAR entries.

Notes

Allocating the SQL descriptor: Before the DESCRIBE TABLE statement is executed, the SQL descriptor must be allocated using the ALLOCATE DESCRIPTOR statement. If the number of descriptor items allocated is less than the number of columns in the table or view, a warning (SQLSTATE 01005) is returned.

Allocating the SQLDA: Before the DESCRIBE TABLE statement is executed, the value of SQLN must be set to a value greater than or equal to zero to indicate how many occurrences of SQLVAR are provided in the SQLDA and enough storage must be allocated to contain SQLN occurrences. To obtain the description of the columns of the table or view, the number of occurrences of SQLVAR must not be less than the number of columns. Furthermore, if USING BOTH or USING ALL is specified, or if the columns include LOBs or distinct types, the number of occurrences of SQLVAR should be two, three, or four times the number of columns. See Determining how many SQLVAR occurrences are needed for more information.

If not enough occurrences are provided to return all sets of occurrences, SQLN is set to the total number of occurrences necessary to return all information. Otherwise, SQLN is set to the number of columns.

For a description of techniques that can be used to allocate the SQLDA, see Appendix D. SQLDA (SQL descriptor area).

Example

In a C program, execute a DESCRIBE statement with an SQLDA that has no occurrences of SQLVAR. If SQLD is greater than zero, use the value to allocate an SQLDA with the necessary number of occurrences of SQLVAR and then execute a DESCRIBE statement using that SQLDA.

  EXEC SQL  BEGIN DECLARE SECTION;
    char table_name[201];
  EXEC SQL  END DECLARE SECTION;
  EXEC SQL  INCLUDE SQLDA;
  EXEC SQL  DECLARE DYN_CURSOR CURSOR FOR STMT1_NAME;

  .../*code to prompt user for a table or view */
  .../*code to set SQLN to zero and to allocate the SQLDA */
  EXEC SQL  DESCRIBE TABLE :table_name INTO :sqlda;    

  ... /* code to check that SQLD is greater than zero, to set */
      /* SQLN to SQLD, then to re-allocate the SQLDA          */
  EXEC SQL  DESCRIBE TABLE :table_name INTO :sqlda;    

  .
  .
  .