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: 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.

Qualifiers

Your subsystem or data sharing group can contain multiple instances of these 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. To upgrade the EXPLAIN tables to the format of the current Db2, you can call the ADMIN_EXPLAIN_MAINT stored procedure. ADMIN_EXPLAIN_MAINT can also create EXPLAIN tables, upgrade them to the format for the current Db2 release, or complete other maintenance tasks. See ADMIN_EXPLAIN_MAINT stored procedure for information about using the action input parameter to request each of these tasks. Alternatively, to perform only the task of upgrading EXPLAIN tables to the format of the current Db2, you can run job DSNTIJXA. DSNTIJXA invokes REXX exec DSNTXTA to perform the upgrade. See Migration step 21: Convert EXPLAIN tables to the current format for more information on running DSNTIJXA.

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, native SQL procedure, or advanced trigger, 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, native SQL procedure, or advanced trigger.
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, native SQL procedure, or advanced trigger, 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. When the SQL statement is embedded in an advanced trigger, this column contains the name of the trigger.
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, native SQL procedure, or advanced trigger, this column indicates the schema name of the compiled SQL function, native SQL procedure, or advanced trigger.
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 PRUNED A query that always returns 0 rows. blank None of the above statement types.
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. If the value is not blank, the value is the same as the VERSION value for the package that was used to create this EXPLAIN table row. The value is blank for a statement in: A package for a basic trigger (TYPE='T') A package for an application that was precompiled without SQL processing option VERSION A package that was precompiled with an empty string for the VERSION value (TYPE=blank) When the SQL statement is embedded in a compiled SQL function or native SQL procedure, this column indicates the version identifier of the function or procedure. When the SQL statement is embedded in an advanced trigger body, this column is not used and will be blank.
EXPANSION_REASON	CHAR(2) NOT NULL WITH DEFAULT	This column applies only to statements that reference archive tables or temporal tables. For other statements, this column is blank. Indicates the effect of the CURRENT TEMPORAL BUSINESS_TIME special register, the CURRENT TEMPORAL SYSTEM_TIME special register, and the SYSIBMADM.GET_ARCHIVE built-in global variable. These items are controlled by the BUSTIMESENSITIVE, SYSTIMESENSITIVE, and ARCHIVESENSITIVE bind options. Db2 implicitly adds certain syntax to the query if one of the following conditions are true: The SYSIBMADM.GET_ARCHIVE global variable is set to Y and the ARCHIVESENSITIVE bind option is set to YES The CURRENT TEMPORAL BUSINESS_TIME special register is not null and the BUSTIMESENSITIVE bind option is set to YES The CURRENT TEMPORAL SYSTEM_TIME special register is not null and the SYSTIMESENSITIVE bind option is set to YES This column can have one of the following values: 'A' The query contains implicit query transformation as a result of the SYSIBMADM.GET_ARCHIVE built-in global variable. 'B' The query contains implicit query transformation as a result of the CURRENT TEMPORAL BUSINESS_TIME special register. 'S' The query contains implicit query transformation as a result of the CURRENT TEMPORAL SYSTEM_TIME special register. 'SB' The query contains implicit query transformation as a result of the CURRENT TEMPORAL SYSTEM_TIME special register and the CURRENT TEMPORAL BUSINESS_TIME special register. blank The query does not contain implicit query transformation.
APCOMPARE_STATUS	CHAR(1) NOT NULL WITH DEFAULT	The status of the access path comparison operation for the APCOMPARE option of a BIND or REBIND command. 'S' Access path comparison succeeded, and the structure of the new access path matches the previous access path. 'F' The structure of the new access path does not match the previous access path, or the access path comparison operation failed. 'N' No match was found. blank This is the default value. APCOMPARE is not used, APCOMPARE was used prior to Db2 12, or APCOMPARE was used before this column was added to the table.
APREUSE_STATUS	CHAR(1) NOT NULL WITH DEFAULT	The status of the access path reuse operation for the APREUSE option of a BIND or REBIND command. 'S' Access path reuse succeeded. 'F' Access path reuse failed. 'N' No match was found. blank This is the default value. APREUSE was not used, APREUSE was used prior to Db2 12, or APREUSE was used before this column was added to the table.
APREUSE_VERSION	VARCHAR(122) NOT NULL WITH DEFAULT	The version identifier for the package. The value is the bind version of the package whose access path is reused. The default value blank is used when APREUSE_STATUS is blank.
APREUSE_COPYID	INTEGER NOT NULL WITH DEFAULT	The copy number of identifier for the package. The value is the copy number of the package whose access plan is being taken to be reused. The default value -1 blank is used when APREUSE_STATUS is blank.
EXPLAIN_TYPE	CHAR(1)	The type of action that created the row: 'A' Automatic bind 'B' BIND command 'C' EXPLAIN STATEMENT CACHE statement 'D' Dynamic EXPLAIN statement 'R' REBIND command 'S' EXPLAIN STABILIZED DYNAMIC QUERY statement. blank The row existed before this column was added to the table. This is the default value.
PER_STMT_ID	BIGINT NOT NULL	The persistent statement identifier for SQL statements in Db2 catalog tables. For example, this column corresponds to the following catalog table columns that identify SQL statements: STMT_ID in SYSIBM.SYSPACKSTMT, for SQL statements in packages. SDQ_STMT_ID in SYSIBM.SYSDYNQUERY, for stabilized dynamic SQL statements.
QUERY_HASH	CHAR(16) NOT NULL FOR BIT DATA	The hash key that is generated by the statement text. This value is not unique for each statement. Other columns for the collection ID, package name, section number, and query number can be used with the hash key for uniqueness.
FUNCTION_LVL	VARCHAR(10) NOT NULL WITH DEFAULT	The function level of the Db2 subsystem when the access path was selected for the statement.
STMT_HASHID2	CHAR(8) FOR BIT DATA	Used to identify an SQL statement. Based on normalized SQL statement text. Includes certain BIND options for static SQL, and PREPARE attributes for dynamic SQL. Includes COLLID and PACKAGE name for static SQL. Excludes COLLID and PACKAGE name for dynamic SQL. Excludes VERSION name for static SQL.
STMT_HASH2VER	INTEGER	Used to identify the version of the hash algorithm that is used to compute the STMT_HASHID2 value.
AP_PLANID	CHAR(16) FOR BIT DATA	A unique identifier for BIND or PREPARE optimizations for an SQL statement, in the form of an extended timestamp value.
AP_PLANHASH	CHAR(16) FOR BIT DATA	Used to identify an access path. Based on selected columns of the PLAN_TABLE which contribute to the access path. Excludes cols that don’t affect the access path, such as APPLNAME, PROGNAME, VERSION, etc.
AP_PLANHASHVER	INTEGER	Used to identify the version of the hash algorithm that is used to compute the AP_PLANHASH value.
AP_SERVICE_DATA	VARCHAR(512) FOR BIT DATA	Used to save optimizer-sensitive environment variables at the time of optimization.
CONNECTION_TYPE	CHAR(8)	Connection type which did the PREPARE or BIND for the statement.
CLIENT_USERID	VARCHAR(128)	The client user ID name information.
CLIENT_APPLNAME	VARCHAR(255)	The client application name information.
CLIENT_WRKSTNNAME	VARCHAR(255)	The client workstation name information.

End program-specific programming interface information.