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A HAVING clause in SQL specifies that an SQL SELECT statement must only return rows where aggregate values meet the specified conditions.
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A HAVING clause in SQL specifies that an SQL SELECT statement must only return rows where aggregate values meet the specified conditions.
HAVING and WHERE are often confused by beginners, but they serve different purposes. WHERE is taken into account at an earlier stage of a query execution, filtering the rows read from the tables. If a query contains GROUP BY, rows from the tables are grouped and aggregated. After the aggregating operation, HAVING is applied, filtering out the rows that don't match the specified conditions. Therefore, WHERE applies to data read from tables, and HAVING should only apply to aggregated data, which isn't known in the initial stage of a query.
To view the present condition formed by the GROUP BY clause, the HAVING clause is used.[ clarification needed ]
To return a list of department IDs whose total sales exceeded $1000 on the date of January 1, 2000, along with the sum of their sales on that date:
SELECTDeptID,SUM(SaleAmount)FROMSalesWHERESaleDate='2000-01-01'GROUPBYDeptIDHAVINGSUM(SaleAmount)>1000Referring to the sample tables in the Join example, the following query will return the list of departments which have more than 1 employee:
SELECTDepartmentName,COUNT(*)FROMEmployeeJOINDepartmentONEmployee.DepartmentID=Department.DepartmentIDGROUPBYDepartmentNameHAVINGCOUNT(*)>1;HAVING is convenient, but not necessary. Code equivalent to the example above, but without using HAVING, might look like:
SELECT*FROM(SELECTDepartmentNameASdeptNam,COUNT(*)ASempCountFROMEmployeeASempJOINDepartmentASdeptONemp.DepartmentID=dept.DepartmentIDGROUPBYdeptNam)ASgrpWHEREgrp.empCount>1;Business System 12, or simply BS12, was one of the first fully relational database management systems, designed and implemented by IBM's Bureau Service subsidiary at the company's international development centre in Uithoorn, Netherlands. Programming started in 1978 and the first version was delivered in 1982. It was never widely used and essentially disappeared soon after the division was shut down in 1985, possibly because IBM and other companies settled on SQL as the standard.
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