How to select column 1 value if exists else column 2 value in PostgresQL?

Question

I want to merge two columns in PostgresQL query by the following rule:

select (column_1 or column_2) as column_3 from my_table

Is there a way to achieve it? Though quite clear, I want to prefer column_1 value as column_3 but if it is null, I would like column_2 value as column_3.

Sorry if this sounds naive, thanks!

The Impaler · Accepted Answer · 2021-06-14 13:41:20Z

5

Use COALESCE(). From the manual 9.18.2. COALESCE:

The COALESCE function returns the first of its arguments that is not null. Null is returned only if all arguments are null.

For example:

select coalesce(column_1, column_2) as column_3 from t

answered Jun 14, 2021 at 13:41

The Impaler

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Comments

Sergeant McFuzzyboots · Accepted Answer · 2022-08-18 20:49:59Z

1

You can simply use coalesce. It will first select the non null value from the options.

select coalesce(column_1,column_2) as column_3 from my_table

You can also use case when

select (case when column_1 is null then column_2 else column1 end) as column_3 from my_table

I would prefer first option.

edited Aug 18, 2022 at 20:49

Sergeant McFuzzyboots

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answered Jun 14, 2021 at 13:44

Kazi Mohammad Ali Nur Romel

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1 Comment

Dmitriy Zhuravlev Over a year ago

It is worth saying that the types of columns are important. If they are not compatible, then there will be an error.

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