Alternative way of writing union in oracle

Alternative ways of writing UNION in Oracle include: direct addition (): join query results and retain duplicate rows. UNION ALL: Join query results, retaining all rows. WITH subquery: Create a temporary table, contain the query results, and then query the temporary table. CTE: Define temporary tables or views for subsequent queries. SQL JOIN: Join related rows in multiple tables.

Alternative way of writing UNION in Oracle

Direct addition ( )

The simplest alternative to UNION is to use the plus () operator. It joins the results of two queries but does not remove duplicate rows.

<code>SELECT * FROM table1 + SELECT * FROM table2;</code>

UNION ALL

UNION ALL is similar to UNION, but it does not remove duplicate rows. It joins the results of two queries and includes all rows in the final result.

<code>SELECT * FROM table1 UNION ALL SELECT * FROM table2;</code>

WITH subquery

WITH subquery allows you to create a temporary table that contains the results of two queries. You can then select from the temporary table.

<code>WITH tmp_table AS (
  SELECT * FROM table1
  UNION
  SELECT * FROM table2
)
SELECT * FROM tmp_table;</code>

Common Table Expression (CTE)

CTE allows you to define temporary tables or views that can be used in subsequent queries. The following example uses CTE instead of UNION:

<code>WITH tmp_table AS (
  SELECT * FROM table1
)
SELECT * FROM tmp_table UNION
SELECT * FROM table2;</code>

SQL JOIN

For UNION involving multiple tables, you can use SQL JOIN. By using join conditions, you can join related rows in different tables.

<code>SELECT *
FROM table1
INNER JOIN table2 ON table1.id = table2.id;</code>

Choose the most appropriate method

The alternative to UNION depends on the specific requirements of the query. Here are some general guidelines:

• If you need to remove duplicate rows, use UNION.
• If you do not need to remove duplicate rows, use UNION ALL, direct addition, or WITH subquery.
• If you need to perform a UNION between multiple tables, consider using SQL JOIN.

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