Using Mysql Union with Same Value

When working with MySQL, there are times when you need to combine data from multiple tables or queries to get a comprehensive view of your data. This can be achieved using the UNION operator in SQL. The UNION operator combines the result-set of two or more SELECT statements into a single result-set.

In this article, we will explore how to use the UNION operator with same value in MySQL. We will also discuss how to handle NULL values when using the UNION operator.

Handling Duplicates

One common issue that arises when using the UNION operator is duplicate rows. By default, the UNION operator removes any redundant duplicate rows from the result set. This means that if two or more queries return the same row, it will only appear once in the final result set.

However, there are times when you want to include all duplicates in your result set, including NULL values. In this case, you can use the ALL keyword with the UNION operator. The ALL keyword includes all rows from both queries, including duplicate NULL values.

Example

Let's consider an example to demonstrate how to use the UNION operator with same value in MySQL. Suppose we have two tables, Cats and Dogs, that contain information about their age and name.

The Cats table contains three rows with NULL values in the Age column.

| FirstName | Age |

|-----------|-----|

| Whiskers | NULL |

| Fluffy | NULL |

| Mittens | NULL |

The Dogs table also contains NULL values in the Age column, but only two instances of NULL.

| Name | Age |

|----------|-----|

| Bark | 10 |

| Fido | NULL |

When we run a query that uses the UNION operator to combine data from both tables, we get the following result:

| FirstName | Age |

|-----------|-----|

| Whiskers | NULL |

| Fluffy | NULL |

| Mittens | NULL |

| Bark | 10 |

| Fido | NULL |

As you can see, the query returns only one instance of NULL even though there are multiple instances of NULL in both tables. This is because the UNION operator removes any redundant duplicate rows from the result set.

In conclusion, using the UNION operator with same value in MySQL allows you to combine data from multiple queries into a single result set. By default, the UNION operator removes any redundant duplicate rows from the result set, but you can use the ALL keyword to include all duplicates, including NULL values. With this knowledge, you can create powerful and flexible queries that provide valuable insights into your data.

* The UNION operator combines the results of two or more SELECT statements into a single result-set.

* By default, the UNION operator removes any redundant duplicate rows from the result set.

* You can use the ALL keyword to include all duplicates, including NULL values, in your result set.

* MySQL treats two NULL values as non-distinct values.

By following these best practices and understanding how to use the UNION operator with same value in MySQL, you can create powerful queries that provide valuable insights into your data.

Mysql union with same value