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what is the difference between union and union all

Answer Posted / leena

union all will combine the outputs of two or more queries.
union will combine the outputs of two or more queries but remove or ignore duplicate value in output.
union all is most faster as compare to union

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create or replace procedure search_matter(empno varchar2) as sql_stmt varchar2(200); stmt varchar2(200); v_table_name varchar2(200); val_pres number; inp_value varchar2(200); type obj_typ is table of cols.column_name%type index by binary_integer; type all_col is table of varchar2(100) index by binary_integer; typ_obj_typ obj_typ; typ_all_col all_col; begin select object_name bulk collect into typ_obj_typ from user_tables,user_objects where table_name = object_name AND object_type = 'TABLE'; select empno into inp_value from dual; dbms_output.put_line('inp value : '||inp_value); for i in typ_obj_typ.first..typ_obj_typ.last loop v_table_name := NULL; v_table_name := typ_obj_typ(i); dbms_output.put_line(i||':'||typ_obj_typ(i)); dbms_output.put_line('....................'); sql_stmt := 'select column_name from cols where table_name = :1 and data_type in (''CHAR'', ''VARCHAR2'', ''NCHAR'', ''NVARCHAR2'',''NUMBER'')'; EXECUTE IMMEDIATE sql_stmt bulk collect into typ_all_col using typ_obj_typ(i); for inside in typ_all_col.first..typ_all_col.last loop dbms_output.put_line('sql stmt: '||sql_stmt); dbms_output.put_line('column name: '||typ_all_col(inside)||'table name: '||typ_obj_typ(i)); stmt := 'select count(*) from ||typ_obj_typ(i)||'; EXECUTE_IMMEDIATE stmt into val_pres ; if val_pres = 1 then dbms_output.put_line('value present col name: '||typ_all_col(inside)||'table name :'||typ_obj_typ(i)); end if; end loop; dbms_output.put_line('....................'); end loop; exception when others then dbms_output.put_line('sql code '||sqlcode||'Table name: '||v_table_name); dbms_output.put_line('sql message '||sqlerrm); end; Compile-time I am getting below error, Plz help to resolve. LINE/COL ERROR -------- ----------------------------------------------------------------- 47/23 PLS-00103: Encountered the symbol "STMT" when expecting one of the following: := . ( @ % ;

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