DSN_STATEMNT_TABLE

The statement table, DSN_STATEMNT_TABLE, contains information about the estimated cost of specified SQL statements.

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 content of each column in STATEMNT_TABLE.

Table 1. Descriptions of columns in DSN_STATEMNT_TABLE
Column name	Data type	Description
QUERYNO	INTEGER NOT NULL WITH DEFAULT	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.
APPLNAME	VARCHAR(24) NOT NULL WITH DEFAULT	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 WITH DEFAULT	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.
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.
GROUP_MEMBER	VARCHAR(24) NOT NULL WITH DEFAULT	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.
EXPLAIN_TIME	TIMESTAMP NOT NULL WITH DEFAULT	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.
STMT_TYPE	CHAR(6) NOT NULL WITH DEFAULT	The type of statement being explained. Possible values are: SELECT SELECT INSERT INSERT UPDATE UPDATE MERGE MERGE DELETE DELETE TRUNCA TRUNCATE SELUPD SELECT with FOR UPDATE OF DELCUR DELETE WHERE CURRENT OF CURSOR UPDCUR UPDATE WHERE CURRENT OF CURSOR
COST_CATEGORY	CHAR(1) NOT NULL WITH DEFAULT	Indicates if DB2 was forced to use default values when making its estimates. Possible values: A Indicates that DB2 had enough information to make a cost estimate without using default values. B Indicates that some condition exists for which DB2 was forced to use default values. See the values in REASON to determine why DB2 was unable to put this estimate in cost category A.
PROCMS	INTEGER NOT NULL WITH DEFAULT	The estimated processor cost, in milliseconds, for the SQL statement. The estimate is rounded up to the next integer value. The maximum value for this cost is 2147483647 milliseconds, which is equivalent to approximately 24.8 days. If the estimated value exceeds this maximum, the maximum value is reported. If an accelerator is used, the difference is reflected in this value.
PROCSU	INTEGER NOT NULL WITH DEFAULT	The estimated processor cost, in service units, for the SQL statement. The estimate is rounded up to the next integer value. The maximum value for this cost is 2147483647 service units. If the estimated value exceeds this maximum, the maximum value is reported. If an accelerator is used, this value represents the estimated cost including any impact of acceleration.
REASON	VARCHAR(254) WITH DEFAULT	A string that indicates the reasons for putting an estimate into cost category B. ACCELMODEL ELIGIBLE The query is eligible for acceleration. ACCELMODEL NOT ELIGIBLE The query is not eligible for acceleration. HAVING CLAUSE A subselect in the SQL statement contains a HAVING clause. HOST VARIABLES The statement uses host variables, parameter markers, or special registers. OPTIMIZATION HINTS An statement-level access path, or PLAN_TABLE access path hint is applied to the statement, or APREUSE(ERROR/WARN) is applied for the package. PROFILEID `value` When profile monitoring is used for the statement, the value of the PROFILEID column in SYSIBM.DSN_PROFILE_TABLE. REFERENTIAL CONSTRAINTS Referential constraints of the type CASCADE or SET NULL exist on the target table of a DELETE statement. TABLE CARDINALITY The cardinality statistics are missing for one or more of the tables that are used in the statement, or the statement used materialized views or table expressions. TRIGGERS Triggers are defined on the target table of an insert, update, or delete operation. UDF The statement uses user-defined functions.
STMT_ENCODE	CHAR(1) WITH DEFAULT	Encoding scheme of the statement. If the statement represents a single CCSID set, the possible values are: A ASCII E EBCDIC U Unicode If the statement has multiple CCSID sets, the value is M.
TOTAL_COST	FLOAT NOT NULL WITH DEFAULT	The overall estimated cost of the statement. If an accelerator is used, the benefit is reflected in this value.. Use this value for reference purposes only. DB2 does not always choose the access path that has the lowest TOTAL_COST value. DB2 also uses other factors during access path selection, such as the reliability of the filter factor estimates.
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.
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.