How Can I Derive a Column Calculation from a Pre-existing Calculated Column in SQL?

Deriving a Column Calculation from a Calculated Column in SQL

In SQL, you may encounter the need to further calculate a column based on a previously calculated column within the same view or query. This can be achieved through various methods.

One approach is to introduce a nested subquery, as demonstrated below:

SELECT
  ColumnA,
  ColumnB,
  calccolumn1,
  calccolumn1 / ColumnC AS calccolumn2
FROM (
  SELECT
    ColumnA,
    ColumnB,
    ColumnC,
    ColumnA + ColumnB AS calccolumn1
  FROM table_name
);

In this query, the subquery calculates the initial column calccolumn1 using the expression ColumnA ColumnB. Subsequently, the outer query references calccolumn1 to calculate calccolumn2.

Alternatively, if the initial calculation is not computationally expensive, you can simply repeat the calculation explicitly in the main query:

SELECT
  ColumnA,
  ColumnB,
  ColumnA + ColumnB AS calccolumn1,
  (ColumnA + ColumnB) / ColumnC AS calccolumn2
FROM table_name;

This approach ensures that both calculations are performed concurrently, without the need for nesting.

By implementing these methods, you can seamlessly derive additional column calculations from existing calculated columns within your SQL queries and views.

The above is the detailed content of How Can I Derive a Column Calculation from a Pre-existing Calculated Column in SQL?. For more information, please follow other related articles on the PHP Chinese website!