How Can I Use an IF Statement to Conditionally Select Values in a SQL SELECT Statement?

Use 'IF' in SELECT statement for conditional value selection

In the following SELECT statement, we want to retrieve the amount column from the report table:

<code class="language-sql">SELECT id, amount
FROM report</code>

However, we need to modify the output based on conditions. If the value of the type column is 'P', we want the amount column to remain unchanged. If the value of the type column is 'N', we want to invert the amount column.

To achieve this, we can use the IF() function in the SELECT statement. The IF() function allows us to specify a logical condition and return different values ​​depending on whether the condition is true or false.

The query modified using the IF() function is:

<code class="language-sql">SELECT id,
       IF(type = 'P', amount, amount * -1) as amount
FROM report</code>

Breakdown of query:

• IF() function checks whether the value of type column is equal to 'P'.
• If the condition is true (i.e. type is 'P'), the original amount value is returned.
• If the condition is false (i.e. type is 'N'), the amount value is multiplied by -1 and inverted.
• The result of the IF() function is assigned to the new column alias amount.

This modified query will generate a modified amount column based on the conditions, providing the desired output.

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