Sql having can be regarded as a WHERE clause for Group By statement. Just as Sql Where limits the rows, so is HAVING clause,but it limits the rows returned by the Group By.
The conditions in HAVING clause can be non-aggregate or aggregate, while in WHERE conditons can only be non aggregates.
Group By clause puts together rows into sets and Having clause puts a conditions on the sets
Example: Use Contact Table, show the State that appears more than once.
|1||White||Alan||210 George St||Sydney||NSW||2000|
|2||Johnson||Benjamin||11 Cooper St||Surry Hill||NSW||2010|
|3||Brown||Peter||72 Haymarket St||Haymarket||NSW||2000|
|4||Anderson||Thomas||33 Collins St||Melbourne||VIC||3000|
|5||Gomdas||Tony||78 Marine Pde||Coolangatta||QLD||4225|
|6||Jones||David||2 Park St||Sydney||NSW||2000|
|7||Gutman||Philip||27 Swanson St||Melbourne||VIC||3000|
Important note on the use of WHERE and HAVING clause. WHERE clause limits the rows before grouping, while HAVING chooses the rows after grouping.
The core of Sql, selecting data from table.
Eliminating duplicate values in the output.
Conditionally selecting rows from table.
Pattern searching for conditions in Where or Having clause
Added to conditions to show results between two values.
It enables us to specify multiple values, either as a list or a subquery.
Sql And Or
Connecting two or more conditions in the Where or Having clause.
Counting number of rows.
Getting the sum of a field
This function will return the highest value.
This function will return the lowest value.
This function will return the average value.
Sql Order By
Sorting the output
Sql Group By
Grouping rows into sets.
Return from Sql Having to Sql Commands
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