Count the number of rows in a schema based on a where condition - sql

Question

I have engine_id column in various tables in the schema. So I want to count the number of rows based on engine_id column in the whole schema where this column exists.
Select count(*)
from table_name
where table_name.engine_id = 8;

Answer 1

Without user-defined PL/SQL, using only built-in Oracle functionality...
Oracle 11g (and maybe even lower) query:
select TC.table_name, X.*
from user_tab_columns TC
cross join xmltable(
'/ROWSET/ROW/CNT'
passing
dbms_xmlgen.getXMLType('
select count(1) as cnt
from '||TC.table_name||'
where &columnName = &columnValueAsLiteral
')
columns
cnt integer
) X
where TC.column_name = '&columnName'
;
Oracle 12c+ query:
select TC.table_name, X.*
from user_tab_columns TC
cross apply xmltable(
'/ROWSET/ROW/CNT'
passing
dbms_xmlgen.getXMLType('
select count(1) as cnt
from '||TC.table_name||'
where &columnName = &columnValueAsLiteral
')
columns
cnt integer
) X
where TC.column_name = '&columnName'
;
In your case supply
&columnName as ENGINE_ID,
&columnValueAsLiteral as 8.
Note: It could also be possible with the with-PLSQL clause of 12c's but I somehow can't make it work, hence I'm not posting that solution here.

Answer 2

These are the steps which you should be following
Get all the tables which have the column.
select table_name from all_tab_columns
where column_name = 'ENGINE_ID';
Create the above as a cursor and run a loop on it
for records in above_cursor
loop
execute immediate 'select count(*) from ' || records.table_name || 'where engine_id = 8' into some_temp_number_var;
some_total_number_var := some_temp_number_var + some_total_number_var;
end loop;

Answer 3

You will need PL code that would query the data dictionary view USER_TABLES to find out which tables have the column you seek and then build a dynamic SQL query as per your filter requirements.
Your function would be something like this:
create or replace function find_count (p_column_name varchar2,
p_column_value number)
return number is
v_sql clob; HERE
v_count number;
begin
for i in (select table_name
from user_tab_cols
where column_name = upper(v_column_name)) loop
v_sql :=
v_sql
|| 'select count(*) as cnt from '
|| i.table_name
|| ' where '
|| p_column_name
|| ' = '
|| p_column_value;
v_sql := v_sql || chr (10) || 'union all ';
end loop;
v_sql := substr (v_sql, 1, length (v_sql) - 11);
v_sql := 'select sum(cnt) from (' || v_sql || ')';
execute immediate v_sql into v_count;
return v_count;
end find_count;
/
You can trigger this function using a query like this:
select find_count('ENTITY_ID', 1012) as engine_count from dual;