MS SQLSERVER:Advanced Query Concepts Copy
- 1. 11 SQL SERVER: ADVANCEDQUERY CONCEPTS
- 2. Advanced QueriesHaving seen the basic concepts of SQL, let us divulge into the advanced query concepts.The Presentation consists of the following portions: Nested Queries
- 3. Any
- 4. In
- 5. HavingNested QueriesNested Queries literally mean ‘a query within another query’. This is exactly what we are about to see. In some cases, the data derived using a select statement becomes inadequate. Here, we pipe the output of this statement into another select statement, till we get the results that we needed. Illustration:Select x1Select x2Select x3t2t3t1Select x4 from t1,t2,t3
- 6. Nested Select QueriesConsider the following tables of the Fisherman database:FishermanFishCatch Table:Now, I wish to find the names of the fishermen who caught a bass (any type). The SQL query would be:select name from fisherman where fishermanid = any(selectfishermanID from FishCatch where fish like ‘%Bass%’)As you can see, any is used to compare a particular record’s field to that of multiple records.
- 7. Nested Select QueriesThe previous query can be rewritten using in as follows:Using ANY:select name from fisherman where fishermanid= any(selectfishermanID from FishCatch where fish like ‘%Bass%’)Using IN:select name from fisherman where fishermanidin(selectfishermanID from FishCatch where fish like ‘%Bass%’)NOTE: When using in remember NOT TO PUT THE ‘=‘ (Equal to ) operator
- 8. Usefulness of having ‘Having’We have seen that there exists a restriction that the aggregate functions cannot be used in the right side of where clause. This syntactical restriction may lead to several inconveniences while programming.To understand this, see the following problem:Find the Fisherman who has caught 2 fishes:We might think of this solution:Select FishermanID from fishTable where count(fish) =2But this doesn’t work as aggregate functions are not allowed on the right-side of where clause. So, how do we solve the problem? ‘Having’ is our answer.
- 9. HavingFind the Fisherman who has caught 2 fishes:Solving with having:Select fishermanID from fishtable group by fishermanidhaving count(fish)=2
- 10. Summary11. Advanced Query Concepts: Nested Select SQL
- 11. In
- 12. Any
- 13. HavingVisit more self help tutorialsPick a tutorial of your choice and browse through it at your own pace.The tutorials section is free, self-guiding and will not involve any additional support.Visit us at www.dataminingtools.net