Carman Scan 1 Software Cardinality Examples

Index Jump Scan. If an index has several columns and a query has predicates on (for example), the first and third column, DB2 can only match the first column (i.e. Use the index structure to find the first occurrence of a match on that column). Iso 9001 audit checklist pdf. It will then have to sequentially scan the index entries for all entries matching that column. Feb 26, 2018 - Carman Scan 1 Software Cardinality. If you change the schema of a table definition in a Database Diagram and then attempt to edit the table.

I've got a complex multi-join query where the optimizer won't pick an index on a TIMESTAMP column even though it results in a smaller index/table scan. If I force the index on the TIMESTAMP column, then the query is much faster; however I can't do this because it's only in a small number of cases when the TIMESTAMP column is the correct index to use (and EXPLAIN seems to confirm this) but MySQL seems to ignore this. The table concerned has a very large number of rows (~300 million, ~50GB with indexes) and the cardinality of the TIMESTAMP column index is very high (SHOW INDEX for the table is below). For example, an EXPLAIN with no index hinting produces this (the equivalent query never completes). Code: SHOW INDEXES FROM rf; Table N_u Key_name Seq Column_name Col.

Cardinality S_p Packed Null Index_type rf 0 PRIMARY 1 rf_id A 313743334 NULL NULL BTREE rf 1 rfs_id 1 rfs_id A 18 NULL NULL BTREE rf 1 rfc_id 1 rfc_id A 18 NULL NULL BTREE rf 1 si_id 1 si_id A 18 NULL NULL BTREE rf 1 me_id 1 me_id A 62748666 NULL NULL YES BTREE rf 1 si_campaign 1 si_id A 18 NULL NULL BTREE rf 1 si_campaign 2 rfc_id A 175471 NULL NULL BTREE rf 1 si_source 1 si_id A 18 NULL NULL BTREE rf 1 si_source 2 rfs_id A 18 NULL NULL BTREE rf 1 rf_timestamp 1 rf_timestamp A 104581111 NULL NULL BTREE. Code: SELECT COUNT(*) FROM rf WHERE rf.si_id = 19570 AND rf.rf_timestamp BETWEEN '2013-06-15 00:00:00' AND NOW(); 1 SIMPLE rf ref si_id,si_campaign,si_source,rf_timestamp si_campaign 4 const 39039810 Using where SELECT COUNT(*) FROM rf FORCE INDEX (rf_timestamp) WHERE rf.si_id = 19570 AND rf.rf_timestamp BETWEEN '2013-06-15 00:00:00' AND NOW(); 1 SIMPLE rf range rf_timestamp rf_timestamp 4 NULL 10457136 Using whereAnd for an si_id with only a handful of rows in the table, the optimized query plan is a better choice. Code: SELECT COUNT(*) FROM rf WHERE rf.si_id = 5913 AND rf.rf_timestamp BETWEEN '2013-06-15 00:00:00' AND NOW(); 1 SIMPLE rf ref si_id,si_campaign,si_source,rf_timestamp si_campaign 4 const 2574 Using where SELECT COUNT(*) FROM rf FORCE INDEX (rf_timestamp) WHERE rf.si_id = 5913 AND rf.rf_timestamp BETWEEN '2013-06-15 00:00:00' AND NOW(); 1 SIMPLE rf range rf_timestamp rf_timestamp 4 NULL 10481348 Using whereIn all of these cases, whatever has the lowest row count for the join on to the rf table is always the quickest query. I want MySQL to make that decision; I can't see a way of doing it myself other than parsing the EXPLAIN output.