Almost correctly.. Look at the joins, you are referring the wrong fields SELECT student.firstname, student.lastname, exam.name, exam.date, grade.grade FROM grade INNER JOIN student ON student.studentId = grade.fk_studentId INNER JOIN exam ON exam.examId = grade.fk_examId ORDER BY exam.date
I think you actually provided a good start for the correct answer right in your question (you just need the correct syntax). I had this exact same problem, and putting DISTINCT in a sub-query was indeed less costly than what other answers here have proposed. select a.FirstName, a.LastName, v.District from AddTbl a inner join (select … Read more
The same as valid UPDATE statement in Postgres: UPDATE incode_warrants iw SET warn_docket_no = iv.viol_docket_no FROM incode_warrantvs iwvs JOIN incode_violations iv ON iv.viol_citation_no = iwvs.warnv_citation_no AND iv.viol_viol_no = iwvs.warnv_viol_no WHERE iw.warn_rid = iwvs.warnv_rid; — AND iw.warn_docket_no IS DISTINCT FROM iv.viol_docket_no — see below You cannot just use a table alias in the FROM clause as … Read more
I did a test on MS SQL 2005 using the following tables: A 400K rows, B 26K rows and C 450 rows. The estimated query plan indicated that the basic inner join would be 3 times slower than the nested sub-queries, however when actually running the query, the basic inner join was twice as fast … Read more
LOOP | HASH | MERGE are Join hints, specifying that the join in the query should use looping, hashing, or merging. Using LOOP |HASH | MERGE JOIN enforces a particular join between two tables. LOOP cannot be specified together with RIGHT or FULL as a join type. You should always use INNER JOIN. Let the … Read more
I always come across this question when searching for how to make LEFT JOIN depend on a further INNER JOIN. Here is an example for what I am searching when I am searching for “using LEFT JOIN and INNER JOIN in the same query”: SELECT * FROM foo f1 LEFT JOIN (bar b1 INNER JOIN … Read more
Flatten Your Criteria You can flatten your multi-dimensional criteria into a single level criteria Now this criteria can be achieved in one query as follow (SELECT * FROM users WHERE gender=”Male” AND region = ‘North’ LIMIT 40) UNION ALL (SELECT * FROM users WHERE gender=”Male” AND region = ‘South’ LIMIT 80) UNION ALL (SELECT * … Read more
Replace INNER JOIN with LEFT JOIN
Just be careful of the difference with outer joins. A query where a filter of b.IsApproved (on the right table, Bar) is added to the ON condition of the JOIN: SELECT * FROM Foo f LEFT OUTER JOIN Bar b ON (b.IsApproved = 1) AND (b.BarId = f.BarId); Is NOT the same as placing the … Read more
If you are allowed to use LINQ, take a look at the following example. It creates two DataTables with integer columns, fills them with some records, join them using LINQ query and outputs them to Console. DataTable dt1 = new DataTable(); dt1.Columns.Add(“CustID”, typeof(int)); dt1.Columns.Add(“ColX”, typeof(int)); dt1.Columns.Add(“ColY”, typeof(int)); DataTable dt2 = new DataTable(); dt2.Columns.Add(“CustID”, typeof(int)); dt2.Columns.Add(“ColZ”, … Read more