A tabela SYSQUERYSEL contém informações sobre a seletividade de predicados para consultas na tabela SYSQUERY que foram identificadas para otimização estendida.
Ele se correlaciona com a tabela SYSQUERY pela coluna QUERYID.
O esquema é SYSIBM.
The SYSQUERYSEL table contains information about the selectivity of predicates for queries in the SYSQUERY table that have been identified for extended optimization.
It correlates to the SYSQUERY table by the QUERYID column.
The schema is SYSIBM.
| Column name |
Data type |
Description |
Use |
| QUERYID |
BIGINT
NOT NULL |
The identifier of the query. |
S |
| 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. |
S |
| 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. |
S |
| 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. |
S |
| 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. |
S |
| SECTNOI |
INTEGER
NOT NULL |
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. |
S |
| COLLID |
VARCHAR(128)
NOT NULL |
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 non-inline SQL function or native SQL procedure, this column is not used and is blank. |
S |
| VERSION |
VARCHAR(122)
NOT NULL |
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 non-inline SQL function or native SQL procedure, this column is not used and is blank. |
S |
| PREDNO |
INTEGER
NOT NULL |
Identifies the predicate |
S |
| INSTANCE |
SMALLINT
NOT NULL |
The selectivity instance, which is used to group related selectivities. |
S |
| SELECTIVITY |
FLOAT
NOT NULL |
The selectivity of the predicate. |
S |
| WEIGHT |
FLOAT (4)
NOT NULL |
The weight of the selectivity instance.
For example, a value of .25 means that 25% of the time when a query is executed the predicate will have this selectivity. |
S |
| ASSUMPTION |
VARCHAR(128)
NOT NULL |
Indicates how the selectivity was estimated, or will be used: One of the following values:
- 'NORMAL'
- Estimated using the normal selectivity assumptions.
- 'OVERRIDE'
- To be used as input to the Optimizer and override it's selectivity estimation.
|
S |
| INSERT_TIME |
TIMESTAMP
NOT NULL
GENERATED ALWAYS
AS ROW CHANGE
TIMESTAMP |
The time when the row was inserted. |
S |
| EXPLAIN_TIME |
TIMESTAMP |
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.
|
S |
| REMARKS |
VARCHAR(762) |
Internal use only. |
S |
