Where statement on two different tables with same column name

Question

Hello,
I have 2 financial tables:
tblincome, tblexpenses
in each table I have column name "monthPayed" (have values of all the months of the year).
I would like to create a balance view table that will show me the financial status for the Q1 (for example).
I have a column totalIncome and totalExpended respectively.
I've create a view table that shows me the financial balance at the moment but I want it to be devide to Quarters of the year...
Regards

Answer 1

 
Please post DDL, so that people do not have to guess what the keys, constraints, Declarative Referential Integrity, data types, etc. in your schema are. Learn how to follow ISO-11179 data element naming conventions and formatting rules. Temporal data should
use ISO-8601 formats. Code should be in Standard SQL as much as possible and not local dialect. 
This is minimal polite behavior on SQL forums. Where is the code you already tried? Or are you so lazy, so rude or so privileged that you did not do anything for yourself? 
In fact that silly “tbl-” prefix is so bad that it has a name! It is called Tibbling and Phil Factor even wrote a humor article on bad programmers that use it. 
Your narrative is vague; it sounds like this is the DDL: 
CREATE TABLE Incomes
(payment_month CHAR(10) NOT NULL PRIMARY KEY,
 income_amt DECIMAL(12,2) NOT NULL
  CHECK (income_amt > 0.00),
CREATE TABLE Expenses
(payment_month CHAR(10) NOT NULL PRIMARY KEY,
 expense_amt DECIMAL(12,2) NOT NULL
  CHECK (expense_amt > 0.00),
>> in each table I have column name "monthPayed" (have values of all the months of the year). <<
I hope not! 2014 has not gotten to September, November or December yet! And the ISO-11179 data element name should be “payment_month”; but it is still wrong! An expense is not a payment! An income is not a payment! 
>> I would like to create a balance view table that will show me the financial status for the Q1 (for example). <<
Report Period Table
Since SQL is a database language, we prefer to do look ups and not calculations. They can be optimized while temporal math messes up optimization. A useful idiom is a report period calendar that everyone uses so there is no way to get disagreements in the DML.
The report period table gives a name to a range of dates that is common to the entire enterprise. 
CREATE TABLE Something_Report_Periods
(something_report_name CHAR(10) NOT NULL PRIMARY KEY
   CHECK (something_report_name LIKE <pattern>),
 something_report_start_date DATE NOT NULL,
 something_report_end_date DATE NOT NULL,
  CONSTRAINT date_ordering
    CHECK (something_report_start_date <= something_report_end_date),
etc);
These report periods can overlap or have gaps. I like the MySQL convention of using double zeroes for months and years, That is 'yyyy-mm-00' for a month within a year and 'yyyy-00-00' for the whole year. The advantages are that it will sort with the ISO-8601
data format required by Standard SQL and it is language independent. The pattern for validation is '[12][0-9][0-9][0-9]-00-00' and '[12][0-9][0-9][0-9]-[01][0-9]-00'
Now figure it out for yourself, show us what effort you put into this, then we will help you. 
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