[[["容易理解","easyToUnderstand","thumb-up"],["確實解決了我的問題","solvedMyProblem","thumb-up"],["其他","otherUp","thumb-up"]],[["難以理解","hardToUnderstand","thumb-down"],["資訊或程式碼範例有誤","incorrectInformationOrSampleCode","thumb-down"],["缺少我需要的資訊/範例","missingTheInformationSamplesINeed","thumb-down"],["翻譯問題","translationIssue","thumb-down"],["其他","otherDown","thumb-down"]],["上次更新時間：2025-07-31 (世界標準時間)。"],[],[],null,["# NULLIF\n\nUse `NULLIF` to selectively replace a specific value in your data with NULL. This can be helpful in situations where a particular value represents missing or invalid data, and you want to explicitly mark it as NULL for further analysis or processing.\n\nSample usage\n------------\n\nReplace -1 in the **Discount** field with NULL.\n\n`NULLIF(Discount, -1)`\n\nSyntax\n------\n\n`NULLIF( `\u003cvar translate=\"no\"\u003einput_expression\u003c/var\u003e`, `\u003cvar translate=\"no\"\u003eexpression_to_match\u003c/var\u003e` )`\n\n### Parameters\n\n#### input_expression\n\nThe expression to evaluate. You can use any valid expression as the \u003cvar translate=\"no\"\u003einput_expression\u003c/var\u003e.\n\n#### expression_to_match\n\n`NULLIF` compares \u003cvar translate=\"no\"\u003eexpression_to_match\u003c/var\u003e to \u003cvar translate=\"no\"\u003einput_expression\u003c/var\u003e. If the two are equal, `NULLIF` returns null, otherwise it returns the \u003cvar translate=\"no\"\u003einput_expression\u003c/var\u003e. You can use any valid expression as the \u003cvar translate=\"no\"\u003eexpression_to_match\u003c/var\u003e.\n\nExample\n-------\n\nSuppose you want to calculate the average discount given to your customers. Your application represents \"no discount\" as -1. The formula `AVG(Discount)` will count -1 and return an incorrect result. To avoid this, you can convert those -1s to NULLS. To do this, create a new field called, for example, **Discount With Nulls** :\n\n`NULLIF(`**`Discount`** `, -1)`\n\nThis formula can be read, \"If the **Discount** field is -1, return null, otherwise return **Discount**.\"\n\nYou can then calculate the average discount ignoring orders with no discount:\n\n`AVG(`**`Discount With Nulls`** `)`"]]
