如何使用WHERE子句泛化实现多值匹配的数组索引查找？

Got it, let's walk through how to adapt your single-value index lookup to work with multiple target values using a WHERE clause. This is a common pattern, and there are a few clean ways to pull it off depending on your needs.

Core Approach: Use the IN Clause #

The simplest and most readable way to match multiple discrete values is with the IN operator. It replaces the single = comparison with a list of target values, making your query concise and easy to maintain.

Example Code #

Suppose your original query for a single value (2) looks like this:

SELECT idx 
FROM your_table 
WHERE A[idx] = 2;

To generalize this to match, say, values 2, 5, and 7, just swap the = with IN and pass your target list:

SELECT idx 
FROM your_table 
WHERE A[idx] IN (2, 5, 7);

Alternative: Using OR (For Simple Cases) #

If you only have a couple of target values, you could chain conditions with OR, but this gets messy quickly as you add more values. It's better to stick with IN for anything beyond 2-3 values.

SELECT idx 
FROM your_table 
WHERE A[idx] = 2 OR A[idx] = 5 OR A[idx] = 7;

Handling Target Values from Another Table #

If your target values are stored in a separate table instead of being hardcoded, you can use a subquery with IN:

-- Assume target values are in a table called target_values with column val
SELECT idx 
FROM your_table 
WHERE A[idx] IN (SELECT val FROM target_values);

Quick Notes #

• Array Indexing: Double-check your database's array index starting position (some use 1, others 0) to make sure you're referencing the correct elements.
• NULL Handling: If your array might contain NULL values and you want to exclude those, add an extra condition: WHERE A[idx] IN (...) AND A[idx] IS NOT NULL.

内容的提问来源于stack exchange，提问作者Mauro Gentile