the MySQL optimizer considers many techniques to efficiently performthe lookups involved in an SQL query. A query on a huge table can be performedwithout reading all the rows; a join involving several tables can be performedwithout comparing every combination of rows. The set of operations...
If SQL query performance is poor or query results do not meet expectations, you can execute the EXPLAIN and EXPLAIN ANALYZE statements in Hologres to obtain execution plans of query statements. This way, you can optimize query statements or database structures. This topic describes how to execute...
Supposethat MIN(c1) can be retrieved by reading one index row and MIN(c2) canbe retrieved by reading one row from a different index. That is, for eachcolumn c1 and c2, thereexists an index where the column is the first column of the index. In thiscase, one row is returned, produced...
In addition to flexible licensing options for SQL Server, there are also Windows Server licensing options that can be taken advantage of. These Windows Server options are known as the Azure Hybrid Benefit (AHB). Similar to applying a SQL Server license you already have purchas...
Arranging your data that way, however, gets in the way of Excel's abilities to use a clean array of data as a database and, based on that, perform the kind of summaries, data extractions--analyses of various types--that Excel excels at. ...
Access method – The way in which the data is being accessed, via either a table scan or index access. Join method – The method (e.g., hash, sort-merge, etc.) used to join tables with each other. Join type – The type of join (e.g., outer, anti, semi, etc...
index) that MySQL actually decided to use. If MySQL decidesto use one of thepossible_keys indexes to look up rows, that index is listedas the key value. It is possiblethat key will namean index that is not present in the possible_keys value.This can happen if none of the possible...
tableThe table and index used in a scan operation in a statement, in the form{table name}@{index name}. spansThe interval of the key space read by the processor.FULL SCANindicates that the table is scanned on all key ranges of the index (also known as a "full table scan" or "unlim...
Node Type:The step PostgreSQL performs (e.g., Seq Scan, Index Scan, Hash Join). Cost:Estimated cost for PostgreSQL to execute the node. Actual Time:The real time taken in milliseconds. Rows:Number of rows processed at each node level. ...
INDEX RANGE SCAN EMP_I1 [ANALYZED] In this case the index is sorted so ther rows will be returned in the order of the index hence a sort is unecessary. SQL> explain plan for select /*+ Full(emp) */ empno,ename from emp where empno> 7876 order by empno; ...