Database Development Tr ươ ng Quý Quỳnh

References UDEMY: SQL Database MasterClass: Go From Pupil To Master! Database Systems - A Practical Approach to Design, Implementation, and Management by Thomas Connolly

Outline Sub-Queries Joins User-defined functions Stored procedures Views SQL profiler, Optimizing

Sub-Queries A Subquery is a Select within a Select or a From or a Where. Example: Select Id,(Select Name from Person where Id=Class.PersonID), PersonID from Class. Select ID, PersonID from (Select * from Class) C. Select ID,PersonID from Class where PersonID in (SelectID from Person where Name=“QuynhTQ”)

Sub-Queries Advantages – To quickly get more data from another Table. – To Optimize a SQL Statement. Disadvantages – Performance issues.

Joins Inner join – When use inner join, you are telling the DB that I have 2 tables and those tables have relationship where value1=value2. – When use inner join, I will not show value from either table or row where this statement is not true. Outer join – Usually used “left outer join”.

User-defined functions Scalar function – Returns only 1 value. – Can not join to scalar function – If you put it in select, it will execute 1 time for every row. Table function – Returns a table variable – Can join to table function

Stored procedures Store procedure is similar to UDFs but returns zero or more values.

Views A view is a way to save a query for later use. A table holds all its data, but view is a smaller portion. Like a window looking to the house at the table.

View Advantages. – Save queries. – Security. Disadvantages. – Performance.

Introduction to SQL profiler

Optimize SQL Remove Scalar UDFs (Replace with view wherever possible) Join properly Move where to join clause if possible Query object order Add indexes Remove cursors