Oracle tree SQL query example

Use this SQL statement

select  * from tree

View the raw data as follows:

The following figure shows the result of a tree query (including the fields root, level, is_leaf, and Path ):

 

Execute the following SQL statement:

select connect_by_root(child_col) root, level , decode(connect_by_isleaf,0,'No',1,'Yes') is_leaf, sys_connect_by_path(child_col,'/') pathfrom treestart with parent_col is null connect by prior child_col=parent_col;

 

 

The focus of tree query is the start with... connect by prior... statement.

And connect_by_root, connect_by_isleaf, and sys_connect_by_path functions. Decode is a common function.

 

 

Other references: http://www.cnblogs.com/tongzhenhua/archive/2008/09/23/1297253.html

 

 

Example of a dynamic query statement:

declare n_rows number; v_sql_stmt varchar2(50); v_table_name varchar2(20); v_name varchar2(20);begin v_table_name := 'tree'; v_sql_stmt := 'select count(*) from ' || v_table_name || ' where parent_col = :1'; v_name := 'asia'; dbms_output.put_line(v_sql_stmt); execute immediate v_sql_stmt into n_rows using v_name; dbms_output.put_line('The number of rows of' || v_table_name || 'is ' || n_rows);end;