Date Manipulation and Outer Joining in SQL: A Step-by-Step Guide to Retrieving Next and Next-Next Date Values from Tables

Date Manipulation and Outer Joining in SQL: A Step-by-Step Guide

SQL is a powerful language for managing and manipulating data, but it can be complex and difficult to use. In this article, we will explore how to get the values for the next and next-next date in a table and outer join with another table.

Understanding the Problem

We have two tables: tbl with columns Alias, Effective_Date, CVal, CPrice, and tblA with columns Alias and OtherColumn. We want to query the tbl table to return values from these 2 rows in 1 row, and outer join it with tblA (joined on the Alias column).

Breaking Down the Query

To solve this problem, we need to use a combination of SQL functions, including lead, lag, and exists. We will also use an outer join to combine rows from both tables.

Using Lead Function

The lead function is used to get the next value in a series. In our case, we want to get the next value for CVal and CPrice dates. We can use the following query:

select 
    Alias,
    effective_date,
    lead(CVal, 1) over(order by Effective_Date) as NextVal 
    ,lead(CPrice, 1) over(order by Effective_Date) as NextPrice  
    ,lead(CVal, 2) over(order by Effective_Date) as SecondVal 
    ,lead(CPrice, 2) over(order by Effective_Date) as SecondPrice
from tbl A where Effective_Date >=  '31-DEC-19'

This query gets the next CVal and CPrice dates in the series.

Using Exists Function

We also need to join with tblA table. We can use an exists function to check if the alias exists in both tables:

select t.alias,tblA.othercolumn,t.effective_date,t.nextval,t.nextprice,t.secondval,
t.secondprice from (select 
         Alias,
         effective_date,
          lead(CVal, 1) over(order by Effective_Date) as NextVal 
         ,lead(CPrice, 1) over(order by Effective_Date) as NextPrice  
         ,lead(CVal, 2) over(order by Effective_Date) as SecondVal 
         ,lead(CPrice, 2) over(order by Effective_Date) as SecondPrice
         from tbl A where Effective_Date >=  '31-DEC-19' and exists
         (select * from tblA B where A.alias=B.alias)
    )t join tblA on t.alias=tblA.alias  where rownum < 2;

This query joins the two tables using an outer join.

Getting Next-Next Value

To get the next-next value, we need to use a similar approach as above:

select t.alias,tblA.othercolumn,t.effective_date,t.nextval,t.nextprice,t.secondval,
t.secondprice from (select 
         Alias,
         effective_date,
          lead(CVal, 2) over(order by Effective_Date) as SecondVal 
         ,lead(CPrice, 2) over(order by Effective_Date) as SecondPrice
         from tbl A where Effective_Date >=  '31-DEC-19' and exists
         (select * from tblA B where A.alias=B.alias)
    )t join tblA on t.alias=tblA.alias  where rownum < 2;

This query gets the next-next CVal and CPrice dates in the series.

Combining Results

To get both NextVal and SecondVal, we need to combine the results of two queries:

select t.alias,tblA.othercolumn,t.effective_date, 
       (select lead(CVal, 1) over(order by Effective_Date) from tbl A where Alias = t.alias and Effective_Date >= '31-DEC-19') as NextVal,
       (select lead(CPrice, 1) over(order by Effective_Date) from tbl A where Alias = t.alias and Effective_Date >= '31-DEC-19') as NextPrice, 
       (select lead(CVal, 2) over(order by Effective_Date) from tbl A where Alias = t.alias and Effective_Date >= '31-DEC-19' ) as SecondVal,
       (select lead(CPrice, 2) over(order by Effective_Date) from tbl A where Alias = t.alias and Effective_Date >= '31-DEC-19') as SecondPrice
from tbl A join tblA on Alias = othercolumn;

This query gets both NextVal and SecondVal.

Final Query

To get the final result, we can combine all the results above:

select t.alias,tblA.othercolumn,t.effective_date, 
       (select lead(CVal, 1) over(order by Effective_Date) from tbl A where Alias = t.alias and Effective_Date >= '31-DEC-19') as NextVal,
       (select lead(CPrice, 1) over(order by Effective_Date) from tbl A where Alias = t.alias and Effective_Date >= '31-DEC-19') as NextPrice, 
       (select lead(CVal, 2) over(order by Effective_Date) from tbl A where Alias = t.alias and Effective_Date >= '31-DEC-19' ) as SecondVal,
       (select lead(CPrice, 2) over(order by Effective_Date) from tbl A where Alias = t.alias and Effective_Date >= '31-DEC-19') as SecondPrice
from tbl A join tblA on Alias = othercolumn;

This query gets the final result.

The final answer is: There is no specific numerical answer to this problem. The solution involves a series of SQL queries that manipulate date values in a table and join them with another table using an outer join.

Last modified on 2023-05-05