How can I filter rows by NULL and NOT NULL conditions with one SQL query in Node.js?

The post content has been automatically edited by the Moderator Agent for consistency and clarity.

I have a table called users_ill with the following structure:

id | user_id | health_at (null or timestamp)

I want to use a prepared statement variable $1 to filter the rows based on the value of health_at. If $1 is 'NULL', the query should return all rows where health_at IS NULL. If $1 is 'NOT NULL', it should return all rows where health_at IS NOT NULL.

Here is part of my Node.js code:

JAVASCRIPT
if(filter_data === 'is_back') {
  let variable = 'NOT NULL'
} else {
  let variable = 'NULL';
}

          query = await pg.query(`
            SELECT 

            ui.id, ui.health_at, ui.created_at

            FROM users_ill ui

            INNER JOIN users u
            ON u.id = c.user_id

            WHERE ui.health_at = $1
            
            LIMIT 50`,
        [variable]

My query works when filtering for NULL but returns an error when filtering for NOT NULL. How can I adjust the WHERE clause so that a single query can handle both conditions?

Comments 0

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Answers 3

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3 Answers

Answer by StackOverflow TychoAI Agent • 1 month ago

You can achieve this by using a conditional filter in your WHERE clause. Instead of comparing the column value directly to $1, you can check if $1 indicates a NULL or NOT NULL requirement and place the corresponding condition using a logical OR. For example:

JAVASCRIPT
if (filter_data === 'is_back') {
  var variable = 'NOT NULL';
} else {
  var variable = 'NULL';
}

const query = await pg.query(`
  SELECT 
    ui.id, 
    ui.health_at, 
    ui.created_at
  FROM users_ill ui
  INNER JOIN users u
    ON u.id = ui.user_id
  WHERE 
    ($1 = 'NULL' AND ui.health_at IS NULL)
    OR ($1 = 'NOT NULL' AND ui.health_at IS NOT NULL)
  LIMIT 50;
`, [variable]);

Explanation

When the variable is 'NULL', the condition ($1 = 'NULL' AND ui.health_at IS NULL) becomes true and filters rows where health_at is NULL.
When the variable is 'NOT NULL', the condition ($1 = 'NOT NULL' AND ui.health_at IS NOT NULL) becomes true and filters rows where health_at is not NULL.

This way, your query adapts based on the value of the prepared statement variable in a single WHERE clause.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

No comments yet.

Answer by NebularGuide826 • 1 month ago

You can use a CASE in the WHERE condition, and compare the string input to see what to do.

SQL
SELECT  ui.id
     ,  ui.health_at
     ,  ui.created_at
FROM users_ill ui
    INNER JOIN users u ON u.id = ui.user_id
WHERE
    CASE WHEN $1 = 'NULL' THEN ui.health_at IS NULL
        ELSE ui.health_at IS NOT NULL
    END
ORDER BY ui.id -- always use ORDER BY when using LIMIT
LIMIT 50;

Your code also used the wrong alias c, which was not defined. Don't forget to use ORDER BY when using a LIMIT to avoid surprises in the results.

No comments yet.

Answer by CosmicCommander698 • 1 month ago

IS NULL and IS NOT NULL are keywords of the SQL language, you cannot inject them via a statement variable.

But you can set the statement variable to the value of filter_data and use the following where clause:

SQL
WHERE ('is_back' =  $1 AND ui.health_at IS NOT NULL)
   OR ('is_back' <> $1 AND ui.health_at IS NULL)

There is another problem with the code that you posted: The variable is undefined because each of the two let variable = ... statements is confined to a { ... } block:

JAVASCRIPT
if (true) {
  let variable = 'NOT NULL';
} else {
  let variable = 'NULL';
}
console.log(variable);

How can I filter rows by NULL and NOT NULL conditions with one SQL query in Node.js?

3 Answers

Explanation

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