JOINS IN SQL SERVERPrepared By Bhagirathi Muduli

JOINSJOIN is a query clause that can be used with the SELECT, UPDATE, and DELETE data query statements to simultaneously affect rows from multiple tables. Joined tables must each include at least one filed in both tables that contain comparable data.

Self Join Inner Join Outer Join Left Outer Join Right Outer Join Full Outer Join Cross Join

SELF JOINIn this circumstance, the same table is specified with different aliases in order to match the data within the same table.

EMP

Write the query to find the corresponding manager name for each employee ?

SELECT A.EMPNO, A.ENAME, A.MGR, B.ENAME, A.JOB, A.SAL, A.DEPTNO FROM EMP A LEFT JOIN EMP B ON A.MGR=B.EMPNO

INNER JOINMatch rows between the defined tables specified in the INNER JOIN statement based on one or more columns having matching data.

SELECT NM.EMPLID, NM.FIRST_NAME, NM.LAST_NAME, DEPT.DEPTID, DEPT.DESCR, JC.JOB_CODE, JC.JOB_DESCR FROM PS_NAMES AS NM INNER JOIN PS_JOB AS JOB ON NM.EMPLID=JOB.EMPLID INNER JOIN PS_JOBCODE AS JC ON JC.JOB_CODE=JOB.JOB_CODE INNER JOIN PS_DEPT_TBL AS DEPT ON DEPT.DEPTID=JOB.DEPTID

OUTER JOINAn OUTER JOIN is a join operation that includes rows that have a match, plus rows that do not have a match in the other table. LEFT OUTER JOINReturns all the rows from the left table in conjunction with the matching rows from the right table. If there are no columns matching in the right table, it returns NULL values.

RIGHT OUTER JOINReturns all the rows from the right table in conjunction with the matching rows from the left table. If there are no columns matching in the left table, it returns NULL values.

FULL OUTER JOINCombines left outer join and right after join. It returns row from either table when the conditions are met and returns null value when there is no match.

LEFT OUTER JOIN Write the query for counting the number of employees according to their respective department and job profile?

SELECT DEPT.DEPTID, DEPT.DESCR, JC.JOB_CODE, JC.JOB_DESCR, COUNT(JOB.EMPLID) AS NO_OF_EMPLOYEE FROM PS_DEPT_TBL AS DEPT LEFT JOIN PS_JOB AS JOB ON DEPT.DEPTID=JOB.DEPTID LEFT JOIN PS_JOBCODE JC ON JC.JOB_CODE=JOB.JOB_CODE GROUP BY DEPT.DEPTID, DEPT.DESCR,JC.JOB_CODE, JC.JOB_DESCR ORDER BY DEPT.DEPTID

RIGHT OUTER JOIN Write the query for finding the detail information about an employee?

SELECT NM.EMPLID,NM.FIRST_NAME+' '+NM.LAST_NAME AS EMPLOYEE_NAME, DEPT.DEPTID, DEPT.DESCR , JC.JOB_CODE, JC.JOB_DESCR FROM PS_DEPT_TBL AS DEPT INNER JOIN PS_JOB AS JOB ON DEPT.DEPTID=JOB.DEPTID INNER JOIN PS_JOBCODE AS JC ON JC.JOB_CODE=JOB.JOB_CODE RIGHT JOIN PS_NAMES AS NM ON NM.EMPLID=JOB.EMPLID

CROSS JOINDoes not necessitate any condition to join. It contains records that are multiplication of record number from both the tables.

SET OPERATION IN SQL SERVER DATABASEThe set operators allow to serially combine more than one select statements. Although more than one select statement will then be present, only one result set is then returned.If the select statements vary in their numbers of returned columns, SQL Server report an error message Msg 205, Level 16, State 1, Line 1 All queries combined using a UNION, INTERSECT or EXCEPT operator must have an equal number of expressions in their target lists.

UNION

INTERSECT

EXCEPT

UNIONQUERY1 UNION [ ALL ] QUERY2 [ ...n ] ] SELECT DEPTID, DESCR FROM PS_JOB UNION SELECT DEPTID, DESCR FROM PS_DEPT_TBLALL TABLES RECORDS

SELECT DEPTID, DESCR FROM PS_JOB UNION ALL SELECT DEPTID, DESCR FROM PS_DEPT_TBL

INTERSECTQUERY1 INTERSECT QUERY2 [ ...n ] ]SELECT DEPTID FROM PS_JOB INTERSECT SELECT DEPTID FROM PS_DEPT_TBL

EXCEPTQUERY1 EXCEPTQUERY2 [ ...n ] ] SELECT DEPTID FROM PS_DEPT_TBL EXCEPT SELECT DEPTID FROM PS_JOB

SUBQUERYA subquery is a SELECT query that returns a single value and is nested inside a SELECT, INSERT, UPDATE, or DELETE statement, or inside another subquery. A subquery can be used anywhere an expression is allowed.

SELECT NM.EMPLID, NM.FIRST_NAME+' ' +NM.LAST_NAME AS EMP_NAME, NM.AGE, DEPT.DESCR FROM PS_NAMES NM LEFT JOIN PS_JOB JOB ON NM.EMPLID=JOB.EMPLID LEFT JOIN PS_DEPT_TBL DEPT ON DEPT.DEPTID=JOB.DEPTID WHERE DEPT.DEPTID = (SELECT DEPTID FROM PS_DEPT_TBL WHERE DESCR='SOFTWARE DEVELOPMENT')