Vantage does not copy statistics under the following scenarios.
Consider this table definition.
CREATE SET TABLE t1, NO FALLBACK, NO BEFORE JOURNAL, NO AFTER JOURNAL, CHECKSUM = DEFAULT ( x INTEGER, y CHAR(10) CHARACTER SET LATIN CASESPECIFIC, z INTEGER) UNIQUE PRIMARY INDEX (x);
Assume that single-column statistics have been collected on columns x, y, and z.
Example1
In this example, Vantage does not copy statistics because only partial data is copied. This occurs because neither y nor z is uniquely constrained, so the system eliminates all duplicate rows, which might cause a difference in cardinality between the 2 tables.
CREATE SET TABLE t9(x, y) AS (SELECT y, z FROM t1) WITH DATA AND STATISTICS PRIMARY INDEX(x, y);
Example2
In this example, Vantage copies partial statistics. The single-column statistics from source table columns x and z are copied as single-column statistics for target table columns a and c, respectively.
Single-column statistics on y in the source table are not eligible to be copied to target table column b in the target table because the NOT CASESPECIFIC column attribute of b is not the same as the column default attribute of source table column y.
CREATE TABLE t9(a, b NOT CASESPECIFIC, c) AS (SELECT x, y, z FROM t1) WITH DATA AND STATISTICS;
Vantage copies these statistics … | From this source table column set … | To this target table column set … | Because … |
---|---|---|---|
single-table | x | a | the columns x and z in source table t1 and columns a and c in target table t9 are identical, so the system copies their single-column statistics. |
z | c | ||
y | none | the definition of column b in the target table is changed from the definition of its analog column y in the source table because it adds a NOT CASESPECIFIC attribute. |
Example3
In this example, single-column statistics on source table column y are not eligible to be copied for target table column x because data for this column is modified in the target table with the UPPERCASE attribute.
CREATE TABLE t9(x UPPERCASE, y) AS (SELECT y, z FROM t1) WITH DATA AND STATISTICS;
Vantage copies these statistics … | From this source table column set … | To this target table column set … | Because … |
---|---|---|---|
single-table | z | y | column z in source table t1 and column y in target table t9 are identical, so the system copies their single-column statistics. |
y | none | the definition of column x in the target table is changed from the definition of its analog column y in the source table because it adds an UPPERCASE attribute. |