SQL Inner Join Performance Data Duplication

Question

table-->qtqstnId tag id1112232422 table-->question qid12 qid primary key, qstnId is Fk now when i run the query-->mysql>selecttagIdfromqtinnerjoinquestiononqt.qstnId=1; it comes back; tag id2121 my question is why am i here Get duplicate data.

P粉022501495 · Answer

filter

qt.qstnId = 1 is a filter clause; it belongs to the WHERE clause.

relation

qt.qstnId = Question.qid Describes how tables are related through JOIN. It belongs to the ON clause after JOIN.

Fix your query; if you still have concerns; provide SHOW CREATE TABLE so we can see if you have the necessary indexes (for performance).

qstnId	tagID
1	1
1	2
2	3
2	4
2	2

tagID
2
1
2
1