Oracle SQL: Generate Rows Based on Quantity Column

In this article, we will explore how to generate rows based on a quantity column in Oracle SQL. We will dive into the world of connect by clauses, multiset functions, and table expressions. Our goal is to create a report that includes separate lines for each headcount and includes the details of the incumbent if available or NULL otherwise.

Introduction

Oracle SQL provides several ways to generate rows based on specific conditions. In this article, we will focus on using the connect by clause and multiset function to achieve our desired result. We will explore how to use these features in conjunction with table expressions and standard ANSI joins.

Understanding Connect By Clauses

A connect by clause is used to create a hierarchical structure from a relational table. It allows us to traverse up or down the hierarchy based on a specific condition. In Oracle SQL, the connect by clause is used extensively for creating hierarchical queries.

The general syntax of a connect by clause is as follows:

SELECT *
FROM table_name
CONNECT BY LEVEL <= condition;

In our case, we are using the following connect by clause to generate rows based on the headcount column:

CONNECT BY LEVEL <= HAP.HEADCOUNT
AND PRIOR HAP.POSITION_ID = HAP.POSITION_ID
AND PRIOR sys_guid() IS NOT NULL;

Understanding Multiset Functions

A multiset function is a set that allows duplicate values. In Oracle SQL, the multiset function returns an array of numbers that can be used as inputs to other functions.

The general syntax of a multiset function is as follows:

CAST(multiset(select condition from dual) AS sys.OdciNumberList);

In our case, we are using the following multiset function to generate an array of levels based on the headcount column:

table(cast(multiset(select level from dual connect by level <= HAP.HEADCOUNT) as sys.OdciNumberList)) lvls;

Table Expressions

A table expression is a way to reference a temporary or permanent table in a SQL query. In Oracle SQL, we can use the table function to create a new temporary table that contains the results of a subquery.

The general syntax of a table expression is as follows:

table subquery;

In our case, we are using the following table expression to generate an array of levels based on the headcount column:

table(cast(multiset(select level from dual connect by level <= HAP.HEADCOUNT) as sys.OdciNumberList)) lvls;

Using Connect By Clauses and Multiset Functions Together

Now that we have understood how to use connect by clauses, multiset functions, and table expressions individually, let’s combine them to generate rows based on the headcount column.

Here is an example query that uses the connect by clause, multiset function, and table expression:

SELECT 
    HAP.NAME POSITION_TITLE,
    HAP.POSITION_CODE,
    PGF.NAME GRADE_NAME,
    PGF.GRADE_CODE,
    HAP.ACTIVE_STATUS,
    HAP.POSITION_TYPE,
    HAP.HEADCOUNT,
    PAAM.ASSIGNMENT_NUMBER,
    Lvls.Column_value row_num

FROM
    HR_ALL_POSITIONS_F_VL HAP, 
    PER_GRADES_F_VL PGF,
    PER_ALL_ASSIGNMENTS_M PAAM,
    table(cast(multiset(select level from dual connect by level <= HAP.HEADCOUNT) as sys.OdciNumberList)) lvls
WHERE 

    HAP.ENTRY_GRADE_ID = PGF.GRADE_ID
AND    PAAM.POSITION_ID(+) = HAP.POSITION_ID
AND      TRUNC(Sysdate) between HAP.effective_start_date AND HAP.effective_end_date
AND      TRUNC(Sysdate) between PGF.effective_start_date AND PGF.effective_end_date
AND      PAAM.effective_start_date(+) <= TRUNC(Sysdate)
AND      PAAM.effective_end_date(+) >= TRUNC(Sysdate);

This query uses the connect by clause to generate rows based on the headcount column and the multiset function to create an array of levels. It also uses a table expression to reference the temporary result set.

Note

Always use standard ANSI joins when combining multiple tables in your queries. In this example, we used the ANSI join syntax (e.g., PAAM.POSITION_ID(+) = HAP.POSITION_ID) instead of the old-style join syntax (e.g., JOIN).

Last modified on 2025-01-20