How to Retrieve Data By Parent and Child Relation

Question

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SQL

CREATE TABLE t1 ( id int , parentid, name String(20) )
 
INSERT INTO t1 VALUES ( 1, NULL, 'Root' )
INSERT INTO t1 VALUES ( 2, 1, 'Branch1' )
INSERT INTO t1 VALUES ( 3, 1, 'Branch2' )
INSERT INTO t1 VALUES ( 4, 3, 'SubBranch1' )
INSERT INTO t1 VALUES ( 5, 2, 'SubBranch2' )

i want to display table as

SQL

root      Branch1         SubBranch1
root      Branch2         SubBranch2

how can i get this one

Posted 2-Jan-16 19:43pm

Prasad Billupati

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Kornfeld Eliyahu Peter · Accepted Answer · 2016-01-02T20:10:00

It may surprise you, but SQL can only handle tabular data...Your desired output depends on the how deep the tree goes - as any new level in the tree should create a new column in the output...
It is possible to create a dynamic query where for every level there is a left join to the original table, but the output will be dynamic too...

SQL

SELECT *
FROM T1
	LEFT JOIN T1 AS T2 ON T2.PARENTID = T1.ID
	LEFT JOIN T1 AS T3 ON T3.PARENTID = T2.ID

So what you really have to do, is revising your requirement and chosen solution for the data layout...