Skip to main content
Version: Next

Data Transformation

Querying​

  • Allows to retrieve data and act on data
  • DDL, DML, DCL, and TCL
  • Life cycle
    • Query issued
    • Parsing and conversion to byte code
    • Query planning and optimization
    • Query execution
    • Result returned
  • Query optimizer
    • It breaks the query into a step into an efficient manner
    • It assess joins, indexes, data size and other factors
    • Attempts to exectute the query in the latest expensive manner
    • Every database (execution engine) is different and execute query in its proper way
    • You need to know how to analyze query's performence
  • Improving query performance
    • Optimize the join strategy and schema
    • Joins types: inner, outer, left and cross
    • Methods
      • Prejoin data
      • Consider the details and the complexity of the joins conditions (complex joins may consumer significate computational resources)
      • Use CTEs instead of subqueries or temporary tables