DSN_STRUCT_TABLE

The structure table, DSN_STRUCT_TABLE, contains information about all of the query blocks in a query.

Begin program-specific programming interface information.

Recommendation: Start of change

Do not manually insert data into system-maintained EXPLAIN tables, and use care when deleting obsolete EXPLAIN table data. The data is intended to be manipulated only by the DB2® EXPLAIN function and optimization tools. Certain optimization tools depend on instances of the various EXPLAIN tables. Be careful not to delete data from or drop instances EXPLAIN tables that are created for these tools. End of change

Qualifiers

Your subsystem or data sharing group can contain more than one of these tables:

'SYSIBM': One instance of this table can be created with the SYSIBM qualifier. DB2 and SQL optimization tools might use the table and the data that it contains. The table is created when you run job DSNTIJSG when you install or migrate DB2.
'user-ID': You can create additional instances of EXPLAIN tables that are qualified by user ID. These tables are populated with statement cost information when you issue the EXPLAIN statement or bind. They are also populated when you specify EXPLAIN(YES) or EXPLAIN(ONLY) in a BIND or REBIND command. SQL optimization tools might also create EXPLAIN tables that are qualified by a user ID. You can find the SQL statement for creating an instance of these tables in member DSNTESC of the SDSNSAMP library.

Sample CREATE TABLE statement

You can find a sample CREATE TABLE statement for each EXPLAIN table in member DSNTESC of the prefix.SDSNSAMP library.

Column descriptions

The following table describes the columns of DSN_STRUCT_TABLE

Table 1. DSN_STRUCT_TABLE description
Column name	Data type	Description
QUERYNO	INTEGER NOT NULL	A number that identifies the statement that is being explained. The origin of the value depends on the context of the row: For rows produced by EXPLAIN statements The number specified in the QUERYNO clause, which is an optional part of the SELECT, INSERT, UPDATE, MERGE, and DELETE statement syntax. For rows not produced by EXPLAIN statements DB2 assigns a number that is based on the line number of the SQL statement in the source program. When the values of QUERYNO are based on the statement number in the source program, values that exceed 32767 are reported as 0. However, in certain rare cases, the value is not guaranteed to be unique. When the SQL statement is embedded in a compiled SQL function or native SQL procedure, if the QUERYNO clause is specified, its value is used by DB2. Otherwise DB2 assigns a number based on the line number of the SQL statement in the compiled SQL function or native SQL procedure.
QBLOCKNO	SMALLINT NOT NULL	A number that identifies each query block within a query. The value of the numbers are not in any particular order, nor are they necessarily consecutive.
APPLNAME	VARCHAR(24) NOT NULL	The name of the application plan for the row. Applies only to embedded EXPLAIN statements that are executed from a plan or to statements that are explained when binding a plan. A blank indicates that the column is not applicable. When the SQL statement is embedded in a compiled SQL function or native SQL procedure, this column is not used, and is blank.
PROGNAME	VARCHAR(128) NOT NULL	The name of the program or package containing the statement being explained. Applies only to embedded EXPLAIN statements and to statements explained as the result of binding a plan or package. A blank indicates that the column is not applicable. When the SQL statement is embedded in a compiled SQL function or native SQL procedure, this column indicates the specific name of the compiled SQL function or native SQL procedure.
PARENT	SMALLINT NOT NULL	The parent query block number of the current query block in the structure of SQL text; this is the same as the PARENT_QBLOCKNO in PLAN_TABLE.
TIMES	FLOAT NOT NULL	The estimated number of rows returned by Data Manager; also the estimated number of times this query block is executed.
ROWCOUNT	INTEGER NOT NULL	The estimated number of rows returned by RDS (Query Cardinality).
ATOPEN	CHAR(1) NOT NULL	Whether the query block is moved up for do-at-open processing; 'Y' if done-at-open; 'N': otherwise.
CONTEXT	CHAR(10) NOT NULL	This column indicates what the context of the current query block is. The possible values are: 'TOP LEVEL' 'UNION' 'UNION ALL' 'PREDICATE' 'TABLE EXP' 'UNKNOWN'
ORDERNO	SMALLINT NOT NULL	Not currently used.
DOATOPEN_PARENT	SMALLINT NOT NULL	The parent query block number of the current query block; Do-at-open parent if the query block is done-at-open, this may be different from the PARENT_QBLOCKNO in PLAN_TABLE.
QBLOCK_TYPE	CHAR(6) NOT NULL WITH DEFAULT	This column indicates the type of the current query block. The possible values are 'SELECT' 'INSERT' 'UPDATE' 'DELETE' 'SELUPD' 'DELCUR' ''UPDCUR' 'CORSUB' 'NCOSUB' 'TABLEX' 'TRIGGR' 'UNION' 'UNIONA' 'CTE' It is equivalent to QBLOCK_TYPE column in PLAN_TABLE, except for CTE.
EXPLAIN_TIME	TIMESTAMP NOT NULL	The time when the EXPLAIN information was captured: All cached statements When the statement entered the cache, in the form of a full-precision timestamp value. Non-cached static statements When the statement was bound, in the form of a full precision timestamp value. Non-cached dynamic statements When EXPLAIN was executed, in the form of a value equivalent to a CHAR(16) representation of the time appended by 4 zeros.
QUERY_STAGE	CHAR(8) NOT NULL	IBM® internal use only.
GROUP_MEMBER	VARCHAR(24) NOT NULL	The member name of the DB2 that executed EXPLAIN. The column is blank if the DB2 subsystem was not in a data sharing environment when EXPLAIN was executed.
ORIGIN	CHAR(1) NOT NULL WITH DEFAULT	Indicates the origin of the query block: Blank Generated by DB2 C Column mask R Row permission U Specified by the user
SECTNOI	INTEGER NOT NULL WITH DEFAULT	The section number of the statement. The value is taken from the same column in SYSPACKSTMT or SYSSTMT tables and can be used to join tables to reconstruct the access path for the statement. This column is applicable only for static statements. The default value of -1 indicates EXPLAIN information that was captured in DB2 9 or earlier.
COLLID	VARCHAR(128) NOT NULL WITH DEFAULT	The collection ID: 'DSNDYNAMICSQLCACHE' The row originates from the dynamic statement cache 'DSNEXPLAINMODEYES' The row originates from an application that specifies YES for the value of the CURRENT EXPLAIN MODE special register. 'DSNEXPLAINMODEEXPLAIN' The row originates from an application that specifies EXPLAIN for the value of the CURRENT EXPLAIN MODE special register. When the SQL statement is embedded in a compiled SQL function or native SQL procedure, this column indicates the schema name of the compiled SQL function or native SQL procedure.
VERSION	VARCHAR(122) NOT NULL WITH DEFAULT	The version identifier for the package. Applies only to an embedded EXPLAIN statement executed from a package or to a statement that is explained when binding a package. A blank indicates that the column is not applicable. When the SQL statement is embedded in a compiled SQL function or native SQL procedure, this column indicates the version identifier of the compiled SQL function or native SQL procedure.

End program-specific programming interface information.