Create using-transform-function-in-snowflake-to-extract-values-from-a-json-array.md

Author: structured-query-language

using-transform-function-in-snowflake-to-extract-values-from-a-json-array.md

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+# Using TRANSFORM function in Snowflake to extract values from a json array
+
+TRANSFORM function in Snowflake can be used for advanced array transformations. You can apply a function or lambda expression to each element in an array and return a new array with the transformed values. Here's the basic syntax:
+
+```sql
+TRANSFORM(input_array, expr)
+```
+
+```sql
+SELECT TRANSFORM([1, 2, 3], x -> x * 2);
+-- Result: [2, 4, 6]
+```
+
+## An Illustrative Example
+Suppose we have a table that has Coupons as a JSON Array for each Sales Order as following
+
+|order_id|coupon_json_array|
+|-----|--------------------------------------------------------------------------|
+| 111 | [{Coupon:"bbb", Discount: -1 }, {Coupon:"aaa", Type:FreeShip}]     |
+| 222 | [{Coupon:"ccc", Discount: -2}]                                        |
+| 333 | [{Coupon:"ccc", Discount: -2}, {Coupon:"aaa"}, {Coupon:"eee"} ] |
+| 444 |                                                                          |
+
+
+For each Order, we need to get the comma-separate list of Coupons, if there are any as following
+
+order_id | coupons_applied
+-- | --
+222 | ccc
+333 | ccc, aaa, eee
+111 | bbb, aaa
+444 |  
+444 |  
+
+We can using the TRANSFORM function to apply a Lambda Fuction to each element in the JSON array to extract the Coupon as following:
+
+```sql
+SELECT
+    order_id,
+    TRANSFORM(
+       parse_json(orders.coupon_json_array)::ARRAY,
+       promo OBJECT -> promo:"Coupon"
+    ) as coupons_applied
+FROM orders;
+```
+
+| order_id | coupons_applied               |
+|----------|-------------------------------|
+| 111      | [   "bbb",   "aaa" ]          |
+| 222      | [   "ccc" ]                   |
+| 333      | [   "ccc",   "aaa",   "eee" ] |
+| 444      |                               |